A critical review on cytogenetics of Cucurbitaceae with updates on Indian taxa

Biplab Kumar Bhowmick; Sumita Jha

doi:10.3897/compcytogen.v16.i2.79033

Review Article

A critical review on cytogenetics of Cucurbitaceae with updates on Indian taxa

Biplab Kumar Bhowmick^‡, Sumita Jha^§

‡ Scottish Church College, Kolkata, India

§ University of Calcutta, Kolkata, India

Corresponding author: Sumita Jha ( sumitajha.cu@gmail.com )

Academic editor: Gennady Karlov

This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Citation: Bhowmick BK, Jha S (2022) A critical review on cytogenetics of Cucurbitaceae with updates on Indian taxa. Comparative Cytogenetics 16(2): 93-126. https://doi.org/10.3897/compcytogen.v16.i2.79033

ZooBank: urn:lsid:zoobank.org:pub:2435F5FD-3686-4E5B-AF32-C873D89B1113

Abstract

The cytogenetic relationships in the species of Cucurbitaceae are becoming immensely important to answer questions pertaining to genome evolution. Here, a simplified and updated data resource on cytogenetics of Cucurbitaceae is presented on the basis of foundational parameters (basic, zygotic and gametic chromosome numbers, ploidy, genome size, karyotype) and molecular cytogenetics. We have revised and collated our own findings on seven agriculturally important Indian cucurbit species in a comparative account with the globally published reports. Chromosome count (of around 19% species) shows nearly three-fold differences while genome size (of nearly 5% species) shows 5.84-fold differences across the species. There is no significant correlation between chromosome numbers and nuclear genome sizes. The possible trend of evolution is discussed here based on molecular cytogenetics data, especially the types and distribution of nucleolus organizer regions (NORs). The review supersedes the scopes of general chromosome databases and invites scopes for continuous updates. The offline resource serves as an exclusive toolkit for research and breeding communities across the globe and also opens scope for future establishment of web-database on Cucurbitaceae cytogenetics.

Keywords

chromosome, genome size, karyotype, NORs, ploidy

Introduction

The family Cucurbitaceae contains an extensive range of diversity consisting of about 1000 species spread over 96 genera (Renner and Schaefer 2017). The diversity of plant families is associated with variation in genome sizes and chromosome numbers as a result of enormous adaptive radiation (Soltis et al. 2004; Lysák and Schubert 2013). The viewpoint of evolution has been changed with the understanding of whole genome duplication (WGD) (Soltis et al. 2014) followed by core-eudicot hexaploidy (Wang et al. 2018). A cytogenetic database is essential to gain insights into evolution by supplementing phylogeny trees with chromosome number information (Mota et al. 2016) to upgrade knowledge on plant systematics (Soltis et al. 2014; Viruel et al. 2021). Cucurbitaceae, being the fourth most important and one of the earliest consumed vegetables yielding family, has coped with extreme climates, extensive human intervention and a huge domestication syndrome (Chomicki et al. 2020). Considerable advances have been made in molecular phylogeny (Renner and Schaefer 2016; Bellot et al. 2020; Chomicki et al. 2020; Guo et al. 2020) and genomics (CuGenDB, http://cucurbitgenomics.org) (Zheng et al. 2019). We had previously discussed about the gaps in cytogenetic studies (Bhowmick and Jha 2015b) which has been surmounted with the advent of molecular cytogenetics.

Currently, we have collated the cytogenetic reports of Cucurbitaceae globally and integrated our own findings for a collective interpretation. The review attempts to address i) the trend of chromosome evolution in specific tribes and species based on available information, ii) correlation between chromosome numbers and ploidy or genome size in the studied taxa and iii) the requirement of an exclusive cytogenetic catalogue for genome researchers, taxonomists and breeders working on Cucurbitaceae.

Methodological approaches

Data compilation

The data have been collated as per Schaefer and Renner (2011) after consultation of books, Chromosome atlases, research articles and public resources like Chromosome Counts Database (CCDB; http://ccdb.tau.ac.il/) (Rice et al. 2015), The Index to Plant Chromosome Numbers (IPCN, http://legacy.tropicos.org/Project/IPCN) (Goldblatt and Lowry 2011) and The Plant DNA C-values database (Pellicer and Leitch 2020) (https://cvalues.science.kew.org/).

Chromosome analysis in the Cucurbit species ocurring in India

Presently an enzymatic maceration and air drying (EMA) method followed by flurochrome banding has been employed as per our previous protocols (Bhowmick et al. 2012, 2016; Bhowmick and Jha 2015a, 2019, 2021) to represent fresh karyotypes of seven agriculturally important cucurbit species (Table 1) belonging to Benincaseae and Sicyoeae. Fresh and healthy roots were used from different sources (like germinating seeds, seedlings and underground root stocks). Roots were pretreated with 0.002 M hydroxyquinoline and fixed in 1:3 aceto-methanol solution. The standardization of EMA- fluorescence banding was conducted for the different species. In brief, fixed roots were digested in enzyme mixture [1% Cellulase (Onozuka RS), 0.75% Macerozyme (R-10), 0.15% Pectolyase (Y-23), 1 mM EDTA] for 40–45 min at 37 °C, macerated on slides, air-dried, stained with 2% Giemsa solution (Merck, Germany) and plates selected for karyotyping. After de-staining, slides were kept in McIlvaine buffer, stained with 0.1 µg mL^-1 DAPI for 15–20 min in darkness. For CMA staining, slides were incubated in 0.1 mg mL^-1 CMA for 15–25 min in darkness. For meiotic chromosomes, fixed anthers were digested in enzyme mixture for 5–8 min, macerated on slides and DAPI staining protocol was followed with minor modifications. All slides were mounted in non-fluorescent glycerol and chromosome plates were observed under a Zeiss Axioscop 2 fluorescence microscope (using UV and BV filter cassettes for DAPI and CMA stains, respectively). Images were captured using the attached ProgRes MFscan Jenoptik D07739 camera and ProgRes CapturePro 2.8.8 software.

Table 1.

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Chromosome numbers and nature of fluorescent bands in some cucurbit species occurring in India.

Tribes	Species (common name, status of cultivation/ wild)	Collection site, Latitude/ Longitude	Fruit image	2n	CMA bands		DAPI bands (Non-nucleolar)
Tribes	Species (common name, status of cultivation/ wild)	Collection site, Latitude/ Longitude	Fruit image	2n	Nucleolar	Non-nucleolar	DAPI bands (Non-nucleolar)
Sicyoeae	Luffa acutangula Linnaeus, 1753 (ridged gourd, cultivated)	Bhubaneswar, Odisha, 20.2960°N, 85.8245°E		26	11^th , 12^th, 13^th	12^th (centromeric)	1^st to 13^th (distal)
	Luffa cylindrica aegyptiaca Miller, 1768 (sponge gourd, cultivated)	Imphal, Manipur, 24.6637°N, 93.906°E		26	12^th , 13^th	1^st , 2^nd (distal)	0
	Luffa echinata Roxburgh, 1814 (wild)	Pantnagar, Uttarakhand, 30.0667°N, 79.019°E		26	11^th , 12^th , 13^th	0	1^st to 13^th (distal)
	Trichosanthes cucumerina Linnaeus, 1753 (wild)	NBPGR, Thrissur, Kerala, 10.5276°N, 76.2144°E		22	10^th , 11^th	0	1^st to 11^th (distal)
	Trichosanthes cucumerina ssp. cucumerina Anguina (snake gourd, cultivated)	Bengaluru, 12.9716°N, 77.5946°E		22	10^th , 11^th	2^nd (distal)	0
	Trichosanthes dioica Roxburgh, 1832 (pointed gourd, cultivated)	Bhagalpur, Bihar, 25.2414°N, 86.9924°E		22 (female)	0	7^th , 8^th , 10^th (distal)	1^st to 11^th
		Bhagalpur, Bihar, 25.2414°N, 86.9924°E		22 (male)	0	0	1^st to 11^th
Benincaseae	Benincasa hispida Thunberg, 1784 (ash gourd, cultivated)	Imphal, Manipur 24.6637°N, 93.906°E		24	12^th	9^th (distal)	0
	Coccinia grandis Linnaeus, 1767 (ivy gourd, restricted cultivation)	Nagpur, Maharashtra, 21.1458°N, 79.0881°E		24 (female)	8^th, 12^th *	1^st to 5^th, 8^th to 12^th (centromeric)	0
		Nagpur, Maharashtra, 21.1458°N, 79.0881°E		24 (male)	8^th, 12^th *	1^st to 5^th, 8^th, 10^th to 12^th (centromeric)	0

Statistical analyses

Statistical analysis involving foundational cytogenetic parameters have been demonstrated to imply significant knowledge on chromosomal evolution within a group (Winterfeld et al. 2020). Considering the lack of hypotheses, we have tested for correlation between the dependent variables (2C genome size, MCL and HCL) and predictor variables [chromosome number (2n) and ploidy level (pl)] and also calculated linear models for regression analysis using IBM SPSS (v23, free).

The modern cytogenetic catalogue of cucurbitaceae

Along with the global review, fresh EMA based somatic plates and idiograms (Figs 1–3) of Indian species are presented here. We retain the previous designation of 10 tribes as ‘understudied’ (Bhowmick and Jha 2015b), excluding Indofevilleeae, having no cytological reports.

Figure 1.

Somatic metaphase chromosomes and idiograms of Luffa species (2n = 26) stained with Giemsa (A, D, G), DAPI (B, E, H) and CMA3 (C, F, I) A–C L. acutangula D–F L. aegyptiaca cylindrica G–I L. echinata. Arrows indicate satellited chromosomes in Giemsa plates and CMA^+ve signals in C, F, I. Corresponding somatic idiograms (haploid set) of: J L. acutangula K L. aegyptiaca L L. echinata, showing DAPI^+ve (blue) and CMA^+ve (golden yellow) bands. Scale Bars: 5 µm

Figure 2.

Somatic metaphase chromosomes and idiograms of Trichosanthes species stained with Giemsa (A, D, I, L), DAPI (C, E, J, M) and CMA3 (B, F, K, N) A–C T. cucumerina ssp. cucumerina (2n = 22), D–F Trichosanthes cucumerina ssp. cucumerina ‘Anguina’ (2n = 22) I–K T. dioica (male, 2n = 22) L–N T. dioica (female, 2n = 22). Arrows indicate satellited chromosomes in Giemsa plates and CMA^+ve signals in B, F, K, N. Corresponding somatic idiograms (haploid set) of: G T. cucumerina ssp. cucumerina H Trichosanthes cucumerina ssp. cucumerina ‘Anguina’ O T. dioica male plant P T. dioica female plant. Blue and golden yellow bands in idiograms indicate DAPI^+ve and CMA^+ve signals, respectively. Scale Bars: 5 µm

Figure 3.

Somatic metaphase chromosomes and idiograms of two Benincaseae species (2n = 24) stained with Giemsa (A, D, G), DAPI (B, E, H) and CMA3 (C, F, I) A–C Benincasa hispida D–F Coccinia grandis (female plant) G–I Coccinia grandis (male plant). Arrows indicate satellited chromosomes in Giemsa plates and distal CMA^+ve signals in C, F, I. Note the longest Y chromosome without any CMA band in G–I and centromeric CMA^+ve signals in F, I. Corresponding somatic idiograms (haploid set) of: J Benincasa hispida K Coccinia grandis (female plant) L Coccinia grandis (male plant) with CMA^+ve (golden yellow) bands. Note the X chromosome remaining indistinguishable in L. Scale Bars: 5 µm

Chromosome numbers

Currently, chromosome counts are available for 188 species (~19%) belonging to about 44 genera (~46%) of the 15 tribes, including the less attended ‘understudied tribes’. Within the ‘understudied tribes’, chromosome counts are available for only 42 species (out of almost 310) belonging to 17 genera (out of nearly 44). The basal number ranges from x/n = 5 (Thladiantha Bunge, 1833) to x/n = 15 (Zanonia Linnaeus, 1753) in these tribes (Table 2). Polyploidy has been abundantly reported in Gomphogyneae. Momordiceae have almost 60 species (Schaefer and Renner 2011) of which reports are known in nearly 11 species. The dibasic condition is noticed in Momordica Linnaeus, 1753 (x = 11 and 14) (Table 3) while polyploidy is detected in M. charantia Linnaeus, 1753 and M. dioica Willdenow, 1805 (2n = 56). M. cymbalaria Hooker, 1871, has the lowest count (2n = 18). In Bryonieae the X-Y sex determination system has been analysed in Bryonia Linnaeus, 1753 as the model along with Ecballium Richard, 1824 (Bhowmick and Jha 2015a). Chromosome counts are reported so far in 10 species of Bryonia (x = 10) and its sister genus Ecballium (x = 12 or x = 9, Table 4). Polyploidy is frequent in Bryonia. Sicyoeae is largest in terms of species (~264–266 species) (Schaefer and Renner 2011) of which cytological reports are known in around 14% species belonging to 9 genera (Table 5). Sicyoeae species range from x = 8 to x = 14 (Table 5). Trichosanthes Linnaeus, 1753 and Luffa Miller, 1754 have x = 11 and x = 13, respectively (Table 1). The less prevalent numbers include x = 12, x = 8 and x = 9 (Table 5). The possibility of multiple base number is noted in Frantzia Pittier, 1910 (x = 12/14) and Sicyos Linnaeus, 1753 (x = 12/13/14). Natural tetraploids are known in two species of Trichosanthes while the majority are diploids. Benincaseae is the second largest tribe comprising of 204–214 species in 24 genera (Schaefer and Renner 2011). Cytological reports are known in around 35% species (76 species of which 41 belong to Cucumis Linnaeus, 1753) of 12 genera (Tables 6, 7). x = 12 is the prevalent condition in Benincaseae (Tables 1, 6, 7). Dual base numbers are noted in the widely studied Cucumis (x = 7, 12). Coccinia Wight et Arnott, 1834 (x = 12) may also possess dual base numbers (x = 10 in C. trilobata Cogniaux, 1895). Molecular cytogenetics of Cucumis sativus Linnaeus, 1753 has demonstrated the evolution of x = 7 from x = 12 in Benincaseae. x = 11 has been confirmed in Citrullus Schrader, 1836 and Lagenaria. The base number of Melothria Linnaeus, 1753, Solena Loureiro, 1790 and Zehneria Endlicher, 1833 can be x = 11 or x = 12 or both (Table 6). Cases of natural polyploidy are noted only in four species of Cucumis (Table 7). Cytogenetic information is available for 17 species in three genera of Cucurbiteae with x = 10 and many polyploids (Table 8). The zygotic chromosome numbers of Luffa, Trichosanthes, Benincasa Savi, 1818 and Coccinia, corroborate the previous reports (Figs 1–3, Table 1).

Table 2.

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Cytogenetic reports in the understudied tribes of Cucurbitaceae #.

Tribe and Genera	Species studied	Chromosome no.			Ploidy, Genome size, Chromosome features	References
Tribe and Genera	Species studied	x	2n	n	Ploidy, Genome size, Chromosome features	References
Gomphogyneae Gomphogyne Griffith, 1845	G. cissiformis Griffith, 1837		32^a	16^b	Tetraploid^c, autopolyploid^d; 10 secondary constrictions, one pair satellited^e; II, III, IV in meiosis^f	CCDB ^b; Kumar and Subramaniam (1987)^a, Singh (1990)^a,d, Roy et al. (1991)^a,c,e,f
Hemsleya F.B. Forbes et Hemsley, 1888	H. amabilis Diels, 1912, H. carnosiflora Wu et Chen, 1985, H. chinensis Forbes et Hemsley, 1888, H. emeiensis Shen et Chang, 1983, H. graciliflora Cogniaux, 1916, H. heterosperma Wallich, 1831, H. macrocarpa Cogniaux, 1916, H. panacis-scandens Wu et Chen, 1985, H. sphaerocarpa Kuang et Lu, 1982	7^a	28^b, 22^c, 24^d, 26^e, 32^f, 40^g, 42^h	14^h	Tetraploidⁱ, aneuploids^j	Samuel et al. (1995) ^a-j, Anmin et al. (2011)^{b, h}
Gynostemma Blume, 1825	G. cardiospermum Oliver, 1892	11^a	66^b		Hexaploid^c	IPCN ^a-c
	G. guangxiense Chen et Qin, 1988		22 ^a		Diploid ^b	IPCN ^a,b
	G. laxiflorum Wu et Chen, 1983		22 ^a		Diploid ^b	IPCN ^a,b
	G. longipes Wu et Chen, 1983		22^a, 44^b		Polyploid^c	IPCN ^a-c
	G. microspermum Wu et Chen, 1983		22^a		Diploid ^b	IPCN ^a,b
	G. pedatum Blume, 1825	12^a	24^b		Diploid^c	Roy et al. (1991) ^a,b,c
	G. pentagynum Wang, 1989		22^a		Diploid ^b	IPCN ^a,b
	G. pentaphyllum Thunberg, 1784		22^a, 24^b, 64^c, 66^d		Diploid^e, triploid^f, hexaploid^g; 2C (flow cytometry): 3.62pg^h; 17M+14sm+2stⁱ; CSR: 2.16–4.09 µm^j 5S (8), 45S (10) rDNA and telomeric signals^k	IPCN ^a,b,c,e,f; Zhang et al. (2013)^h, Pellerin et al. (2018)^d,g,i,j,k
	G. pentaphyllum var. dasycarpum Wu, 1983		22^a, 33^b, 44^c		Polyploid^d	IPCN ^a-d
	G. pentaphyllum var. pentaphyllum Thunberg, 1784		22^a, 44^b, 66^c, 88^d		Polyploid^e	IPCN ^a-e
	G. yixingense Wang et Xie, 1981		88^a		Polyploid^b	IPCN ^a,b
Triceratieae		8^a			-	Roy et al. (1991) ^a
Fevillea Linnaeus, 1753		8^a			-	Roy et al. (1991) ^a
Zanonieae Zanonia Linnaeus, 1753	Z. indica Linnaeus, 1759	15^a	30^b	15^c	Autoploid^d; Metacentric chromosomes^e; CSR: 1.10-1.98 μm^f	Lekhak et al. (2018) ^a-f
Actinostemmateae	A. lobatum (Maxim.) Maxim. ex Franch. & Sav.		16^a		-	IPCN ^a
Actinostemma Griffith, 1841	A. tenerum Griffith, 1837		16^a		Diploid^b; 7M +1sm^c; CSR: 2.88–4.02 µm^d; 45S (1) rDNA and 45S+5S (1) rDNA adjacent signal^e; telomeric repeat signals^f	Pellerin et al. (2018) ^a-f
Thladiantheae	T. calcarata Clarke, 1876, T. cordifolia Blume, 1826 T. davidii Franchet, 1886, T. dentata Cogniaux, 1916, T. lijiangensis Lu et Zhang, 1981, T. nudiflora Hemsley, 1887, T. pustulata Léveillé, 1916
Thladiantha Bunge, 1833		3^a, 5^b, 9^c	18^d	5^e, 9^f	Diploid^g	Darlington and Janaki Ammal (1945) ^c; Roy et al. (1991)^a,b,d,e,g, IPCN^d,f
Thladiantha Bunge, 1833	T. dubia Bunge, 1833	3^a, 5^b, 9^c	18^a, 22^b	5^e, 9^f	Diploid^c; 7M+1sm+1st^d; CSR: 2.60–4.10 µm^e; 45S (4) and co-localized 45S+5S (1) rDNA signals^f; telomeric repeat signals^g	Samuel et al. (1995) ^b, Pellerin et al. (2018)^a,c,d,e,f,g
Baijiania Lu et Li, 1993	B. yunnanensis Lu et Zhang, 1984		32^a		-	IPCN ^a
Siraitieae Siraitia Merrill, 1934	S. grosvenorii Swingle, 1941		28^a		45S (6) and 5S (2) rDNA signals^b	IPCN ^a, Li et al. (2007)^b
Joliffieae Telfairia Hooker, 1827	T. occidentalis Hooker, 1871		22^a, 33^b, 44^c		Diploid^d, aneuploid^e, triploid^f, Tetraploid^g; 1 B^h	Uguru and Onovo (2011) ^a-h
Joliffieae Telfairia Hooker, 1827	T. pedata Sims, 1826		22^a		-	Bhowmick and Jha (2015)^a
Schizopeponeae Herpetospermum Hooker, 1867	H. pedunculosum Seringe, 1828			11^a	45S (14), 5S (2) rDNA signals^b	Xie et al. (2019a) ^a,b
Schizopepon Maximowicz, 1859	S. bryoniifolius Maximowicz, 1859	10^a	20^b		-	Roy et al. (1991) ^a, IPCN^b
Coniandreae Apodanthera Arnott, 1841	A. undulata Gray, 1853	14^a			-	IPCN ^a
Corallocarpus Bentham et Hooker, 1867	C. epigaeus Rottler, 1803		26^a	13^b	-	Beevy and Kuriachan (1996) ^a,b
Corallocarpus Bentham et Hooker, 1867	C. welwitschii Naudin, 1863		72^a		-	Singh (1990)^a
Ibervillea Greene, 1895		11^a, 12^b			-	Darlington and Janaki Ammal (1945) ^a,b
Kedrostis Medikus, 1791	K. africana Linnaeus, 1753		40^a		2C (feulgen densitometry): 0.8 pg^b; 2C (flow cytometry): 1674 Mbp^c	Bennet et al. (1982)^a,b, Plant C DNA Values Database^c
	K. foetidissima Jacquin, 1788		26^a	13^b		Beevy and Kuriachan (1996) ^a,b
	K. rostrata Rottler, 1803	13^a	26^b	13^c	-	IPCN ^a-c
Seyrigia Keraudren, 1960				13^a	-	IPCN ^a

Table 3.

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Cytogenetic information in Momordica (Momordiceae)#.

Species	Chromosome no.		Ploidy, Genome size, Chromosome features	References
Species	2n	n	Ploidy, Genome size, Chromosome features	References
M. balsamina Linnaeus, 1753	22^a		Diploid^b; two chromosomes with double constrictions^c; CSR:0.65–1.98µm^d; MCL:1.30µm^e; TCL: 28.61µm^f	Bharathi et al. (2011) ^a-f
M. charantia	22^a	11^b	Diploid^e, 2C (Feulgen densitometry): 4.10pg ^f, 2C (flow cytometry): 1.43pg^g; chromosomes mostly metacentric, few submetacentric and subtelocentric^h; 2 chromosomes with satellitesⁱ; CSR: 1.26-1.81µm^j; 45S (4) and 5S (2) rDNA signals^k	Plant DNA C-Values Database^f; Bharathi et al. (2011)^a,i ; Barow and Meister (2003)^g; Lombello and Pinto-Maglio (2007)^a,b,h; Bharathi et al. (2011); Waminal and Kim (2012)^a,e,h,j,k; Kausar et al. (2015)^a; Kido et al. (2016)^a,i
M. charantia var. charantia	22^a	11^b	Diploid^c; 2C (flow cytometry): 0.72pg^d; NORs: 4^e; nucleolar and centromeric CMA⁺ bands^f ; CSR: 1.27-3.07µm^g; MCL: 1.97 µm^h; HCL: 21.77µmⁱ	Ghosh et al. (2018) ^a-f; Ghosh et al. (2021)^a,c,d,g,h,i
M. charantia var. muricata Chakravarty, 1982	22^a	11^b	Diploid^c; 2C (flow cytometry): 1.16pg^d; NORs: 6^e; nucleolar and centromeric CMA⁺ bands^f; CSR: 1.64-3.13µm^g; MCL: 2.19µm^h; HCL: 24.19µmⁱ	Ghosh et al. (2018) ^a-f; Ghosh et al. (2021)^a,c,d,g,h,i
M. cochinchinensis Loureiro, 1790	28^a	14^b	Diploid^c, 2C (flow cytometry): 2.64pg^d, 6^e chromosomes with secondary constrictions; CSR:1.16–2.03µm^f /1.71-3.17μm^g ; MCL: 2.27µm^h; HCL: 31.86μmⁱ; 45S (8) and 5S (2) rDNA signals^j	IPCN ^b; Xie et al. (2019a)^a,j; Bharathi et al. (2011)^a,e,f; Ghosh et al. (2021)^a,c,d,g,h,i
M. cymbalaria	18^a	8^b, 9^c, 11^d	Diploid^e, 2C (flow cytometry): 3.74 pg^f; 2^g–4^h chromosomes with secondary constrictions; CSR: 2.71-4.57μmⁱ; MCL:3.75μm^j; HCL: 33.79μm^k	IPCN ^b; CCDB^b,d; Bharathi et al. (2011)^a,c,e,g; Ghosh et al. (2021)^{a,e,f,h,i,j,k}
M. denudata Clarke, 1879		14^a	-	IPCN ^a
M. dioica Willdenow, 1805	28^a, 56^b		Diploid^c; 2C (flow cytometry): 3.36 pg^d, 2^e-12^f chromosomes with secondary constrictions; CSR: 2.04-3.58μm^g; MCL: 2.75µm^h; HCL: 77.10μmⁱ; 45S (4) and 5S (2) rDNA signals^j	Bharathi et al. (2011) ^a,c,e; Xie et al. (2019a)^a,j; Ghosh et al. (2021)^b,d,f,g,h,i
M. foetida Schumacher, 1827	44^a		-	Behera et al. (2011)^a
M. rostrata Zimmermann, 1922	22^a		-	Behera et al. (2011)^a
M. sahyadrica Kattukunnel et Antony, 2007	28^a		2 chromosomes with secondary constrictions^b; CSR: 0.73–1.83µm^c; TCL: 37.53µm^d, MCL: 1.34µm^e	Behera et al. (2011)^a-e
M. subangulata Blume, 1826	56^a		2C (flow cytometry): 3.06pg^b; 8 chromosomes with secondary constrictions^c; CSR: 1.52-3.11μm^d; HCL: 60.30μm^e	Ghosh et al. (2021) ^a-e
M. subangulata subsp. renigera Don, 1834	56^a		4 chromosomes with secondary constrictions^b; CSR: 0.52-1.26µm^c; MCL: 0.93µm^d; TCL 51.88µm^e	Bharathi et al. (2011) ^a-e
M. tuberosa Miquel, 1855	22^a	11^b	-	IPCN ^a,b; CCDB^a,b

Table 4.

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Chromosome number and genome size in Bryonieae#.

Genera	Species studied	Chromosome no.			Genome size	References
Genera	Species studied	x	2n	n	Genome size	References
Bryonia		10^a				Darlington and Janaki Ammal (1945) ^a
	B. alba Linnaeus, 1753	10^a	20^b	10^c	2C (flow cytometry): 5827Mbp^d	CCDB ^d , Volz and Renner (2008) ^a,b,c
	B. aspera Ledebour, 1843	10^a	40^b, 60^c	20^d, 10^e	-	Kumar and Subramaniam (1987) ^c, Volz and Renner (2008)^a,b,d,e
	B . cretica Linnaeus, 1753	10^a	60^b	30^c	-	Volz and Renner (2008) ^a,b,c
	B. dioica Jacquin, 1774	10^a	20^b	10^c	2C (microdensitometry): 4.01pg^d; 2C (flow cytometry): 5522Mbp^e	CCDB ^d,e, Volz and Renner (2008)^a,b,c
	B. macrostylis Heilbronn et Bilge, 1954			10^a	-	IPCN ^a
	B . marmorata Petit, 1889		40^a	20^b	-	Volz and Renner (2008) ^a,b
	B . monoica Aitchison et Hemsley, 1886	10^a	20^b		-	Volz and Renner (2008) ^a,b
	B. multiflora Boissier et Heldreich, 1849	10^a			-	Volz and Renner (2008) ^a
	B. syriaca Boissier, 1856	10^a	20^b		-	Volz and Renner (2008) ^a,b
	B. verrucosa Aiton, 1789	10^a	20^b	10^c	2C (flow cytometry): 2.09pg^d; 4504Mbp^e	CCDB ^d,e, Volz and Renner (2008)^a–c
Ecballium		12^a				Darlington and Janaki Ammal (1945) ^a
	E. elaterium Linnaeus, 1753		18^a	12^b	2C (flow cytometry): 2442Mbp^c	Veselý (2012)^c , Volz and Renner (2008)^b
	E. elaterium subsp. dioicum Battandier, 1989		18^a, 24^b	9^c, 12^d	-	Volz and Renner (2008) ^a-d
	E. elaterium Linnaeus, 1753 subsp. elaterium		18^a	9^b	-	Volz and Renner (2008) ^a,b

Table 5.

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Cytogenetic information in Sicyoeae#.

Genera studied	Species studied	Chromosome no.			Ploidy, Genome size, Chromosome features	References
Genera studied	Species studied	x	2n	n	Ploidy, Genome size, Chromosome features	References
Cyclanthera Lilja, 1870		8^a				Darlington and Janaki Ammal (1945) ^a
Cyclanthera Lilja, 1870	C. pedata (L.) Schrader, 1831		16^a, 32^b	8^c	Diploid^e	Roy et al. (1991) ^a,c,e, Samuel et al. (1995)^b
Echinocystis Torrey et Gray, 1840		8^a		16^b		Bhowmick and Jha (2015b) ^b, Darlington and Janaki Ammal (1945)^a
	E. lobata Michaux, 1803		16^a, 32^b		Tetraploid^c; 2C (flow cytometry):1.49pg^d	IPCN ^a,b, Plant DNA C-Values Database ^c,d
	E. macrocarpa Greene, 1885		32^a		-	Whitaker (1950) ^a
Echinopepon Naudin, 1866	E. wrightii Gray, 1853			12^a	-	IPCN ^a, CCDB^a
Frantzia				12^a, 14^b	-	Schaefer and Renner (2011)^a,b
Hodgsonia Persson, 1953	H. macrocarpa var. capniocarpa Ridley, 1920		18^a		-	IPCN ^a, CCDB^a
Luffa		13^a				Darlington and Janaki Ammal (1945) ^a
	L. acutangula	13^a	26^b	13^c	Diploid^d; CSR:1.39–3.20μm^e; 18m+2sm+6m.st^f; NORs:6^g; distal DAPI and nucleolar CMA signals^h	Kumar and Subramaniam (1987) ^a,b, IPCN^c, Bhowmick and Jha (2021)^b,d-h
	L. acutangula var. acutangula			13^a	-	Beevy and Kuriachan (1996) ^a
	L. acutangula var. amara Clarke, 1879			13^a	-	Beevy and Kuriachan (1996) ^a
	L. aegyptiaca (syn L. cylindrica Roemer, 1846)	13^a	26^b	13^c	Diploid^d, 2C (flow cytometry): 1.56 pg^e; 2C (Feulgen densitometry): 1.7pg^f; CSR: 1.60–2.06μm^g; 24M+1sm^h; 22m+ 4m.stⁱ; NORs:2^j; nucleolar and distal CMA signals^k; 45S (10) and 5S (2) rDNA signals^l	Bennet et al. (1982)^b,d,f, Kumar and Subramaniam (1987)^a,b, Waminal and Kim (2012)^b,d,g,h,l, Bhowmick and Jha (2015a)^{b,c,d,e,i,j,k}
	L. echinata		26^a, 39^b, 52^c	13^d	Diploid^e; CSR 2.44–3.96 μm^f; 16m+4sm+6m.st^g; NORs: 6^h; Distal and intercalary DAPI and nucleolar CMA signalsⁱ	Kumar and Subramaniam (1987) ^a-e, Bhowmick and Jha (2021)^a,e-i
	L. graveolens Roxburgh, 1832	13^a			-	Kumar and Subramaniam (1987) ^a
	L. hermaphrodita Singh et Bhandari, 1963			13^a	-	IPCN ^a
	L. operculata Linnaeus, 1759	13^a	26^b	13^c	-	Kumar and Subramaniam (1987) ^a,b, IPCN^c
Sicyos (75, includes Sechium, Microsechium)		12^a	24^b		-	Darlington and Janaki Ammal (1945) ^a,b
	S. angulatus	12^a	24^b		Diploid^c; CSR: 1.9-4.6µm^d; 4 adjacent 45S+5S rDNA signals^e	Waminal and Kim (2015) ^a-e; IPCN^b
	S. australis Endlicher, 1833		24^a, 26^b		12II^c, 13II^d	IPCN ^a-d, CCDB^a-d
	S. edulis Jacquin, 1760 (syn of Sechium edule)	13^a	26^b, 28^c	12^d, 13^e	Diploid^f; metacentric and submetaccentric chromosomes^g; CSR: 2.69–5.38µm^h; 45S (6), 5S (2) rDNA and telomeric repeat signals (28)ⁱ	Beevy and Kuriachan (1996) ^a,b,e, Pellerin et al. (2018)^c,f,g,h,i, Ting et al. (2019)^c, IPCN^d, CCDB^d
	S. nihoaensis St. John, 1970			12^a	-	IPCN ^a, CCDB^a
	Sechium compositum Smith, 1903 (syn. Microsechium compositum)			14^a	-	IPCN ^a, CCDB^a
	S. hintonii Wilson, 1958 (syn Microsechium hintonii)			14^a	-	IPCN ^a, CCDB^a
Trichosanthes (100)		11^a				Darlington and Janaki Ammal (1945) ^a
	T. anaimalaiensis Beddome, 1864		22^a	11^b	-	Beevy and Kuriachan (1996) ^a,b
	T. boninensis Nakai et Tuyama, 1928		22^a		-	IPCN ^a
	T. bracteata Lamarck, 1797	11^a	22^b, 44^c, 66^d		-	Kumar and Subramaniam (1987) ^a,b, Roy et al. (1991)^c,d
	T. bracteata var. bracteata			11^a, 22^b	-	Beevy and Kuriachan (1996) ^a,b
	T. chingiana Handel-Mazzetti, 1936		22^a		-	IPCN ^a
	T. costata Blume, 1826 (syn Gymnopetalum chinense Loureiro, 1790)		22^a		Diploid^b; 45S (6) and 5S (4) rDNA signals^c	Kumar and Subramaniam (1987) ^a, Xie et al. (2019a)^b,c
	T. cucumerina		22^a	11^b	Diploid^c; 12m+4M+2sm+4sm.st^d; CSR: 2.26–4.99µm^e; 6 chromosomes with double constrictions^f; NORs: 4^g; nucleolar CMA and distal DAPI bands^h	Bhowmick and Jha (2019) ^a-h
	T. cucumerina ssp. cucumerina Anguina	11^a	22^b	11^c, 22^d, 32^e, 33^f	Diploid^e; 2C (Feulgen densitometry): 2.2pg^f; CSR: 2.77–5.01μm^g; 12m+4M+2sm+4sm.st^h; 6 chromosomes with double constrictionsⁱ; NORs: 4^j; nucleolar and distal CMA bands^k; 45S (6) and 5S (2) rDNA signals^l	Kumar and Subramaniam (1987) ^a, Bhowmick and Jha (2019)^{b,c,e,g,h,i,j,k}, Xie et al. (2019a)^b,l, IPCN^c-f
	T. dioica	11^a	22^b	11^c	Diploid^d; 2C (flow cytometry): male-2.27pg, female- 2.32 pg^e; 12m+6Sm +2St+2Sm.t^f; distal DAPI bands^g; distal CMA bands in females^h; 1 rod bivalent in meiosisⁱ	Kumar and Subramaniam (1987) ^a, Guha et al. (2004)^b,d,f,h, Bhowmick and Jha (2015a)^{b,c,d,e,f,g,h,i}
	T. dunniana Léveillé, 1911		22^a		Diploid^b; 45S (6) and 5S (2) rDNA signals^c	Xie et al. (2019a) ^a-c
	T. himalensis Clarke, 1879			11^a	-	Roy et al. (1991) ^a
	T. hupehensis Cheng et Yueh, 1974		22^a		-	IPCN ^a, CCDB^a
	T. kirilowii Maximowicz, 1859		60^a, 66^b, 88^c, 110^d		Hexa-, octa-, decaploid^e;CSR: 2.3-3.5μm^f; 45S (4), 5S (4) and 45S +5S (6) adjacent rDNA signals^g	IPCN ^a, CCDB^a, Waminal and Kim (2015)^b,c,d,e-g
	T. kirilowii var. japonica			11^a	-	Roy and Saran (1990)^a
	T. lepiniana Naudin, 1868		44^a	11^b	1 B^c	Roy et al. (1991) ^b,c, IPCN^a, CCDB^a
	T. lobata Roxburgh, 1832	11^a		11^b	-	Kumar and Subramaniam (1987) ^a, Beevy and Kuriachan (1996)^b
	T. mianyangensis Yueh et. Liao, 1992		88^a		-	IPCN ^a, CCDB^a
	T. nervifolia Linnaeus, 1753			11^a	-	Beevy and Kuriachan (1996) ^a
	T. ovigera Blume, 1826		22^a		Diploid^b; 45S (10) and 5S (2) rDNA signals^c	Xie et al. (2019a) ^a-c
	T. palmata Linnaeus, 1759		22^a, 44^b, 66^c	11^d		IPCN ^a-d
	T. pedata Merril et Chun, 1934		22^a		-	IPCN ^a, CCDB^a
	T. truncata Clarke, 1879		22^a		-	IPCN ^a, CCDB^a
	T. wallichiana Wight, 1840	11^a	22^b		-	Kumar and Subramaniam (1987) ^a,b

Table 6.

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Cytogenetic information on Benincaseae#.

Genera studied	Species studied	Chromosome no.			Ploidy, Genome size, Chromosome features	References
Genera studied	Species studied	x	2n	n	Ploidy, Genome size, Chromosome features	References
Benincasa	B. fistulosa		24^a		Diploid^b; 45S (4) and 5S (4) signals^c	Li et al. (2016) ^a,b,c
Benincasa	B. hispida	12^a	24^b	12^c	Diploid^d; 2C (flow cytometry):1.97pg^e, 2C (feulgen densitometry):2.1pg^f; CSR 2.54-4.59µm^g; 16m+6Sm+2Sm.t^h; NORs:2ⁱ; distal CMA signals^j; 45S (2) and 45S+5S (2) adjacent rDNA signals^k	Plant DNA C-Values Database^f, Waminal et al. (2011)^b,d,g,k, Bhowmick and Jha (2015a)^{b,c,d,e,h,i,j}
Citrullus		11^a				Darlington and Janaki Ammal (1945) ^a
	C. amarus (syn. C. lanatus var. citroides)	11^a	22^b		Diploid^c; CSR: 3.1–4.7μm^d; 45S (2) and 5S (4) rDNA signals^e	Reddy et al. (2013) ^b-d, Waminal and Kim (2015)^a-e, Renner et al. (2017)^b
	C. colocynthis		22^a	11^b	Diploid^c; 45S (2) and 45S+5S (2) adjacent rDNA signals^d	Beevy and Kuriachan (1996) ^b, Reddy et al. (2013)^a,c,d, Li et al. (2016)^a,c,d
	C. ecirrhosus		22^a	11^b	Diploid^c; 2 satellites detected in meiosis^d; 45S (2) and 5S (4) rDNA signals^e; regular meiosis^f	Li et al. (2016) ^a,c,e, Renner et al. (2017)^a,b,c,d,f
	C. lanatus		22^a	11^b	Diploid^c; CSR: 1.09μm-1.72μm^d; 14m+8sm^e; 45S (2) and 45S+5S (2) adjacent rDNA signals^f; linkage groups hybridized to chromosomes^g	Beevy and Kuriachan (1996) ^b, Waminal et al. (2011)^a,c,d,e,f, Ren et al. (2012)^a,c,g
	C. lanatus subsp. lanatus		22^a		Diploid^b; 45S (2) and 5S (4) rDNA signals^c	Li et al. (2016) ^a-c
	C. lanatus subsp. mucosospermus Fursa, 1972		22^a		Diploid^b; 45S (2) and 45S+5S (2) adjacent rDNA signals^c	Li et al. (2016) ^a-c
	C. lanatus subsp. vulgaris Schrader, 1836		22^a		Diploid^b; 45S (2) and 45S+5S (2) adjacent rDNA signals^c	Li et al. (2016) ^a-c
	C. lanatus var. lanatus		22^a		Diploid^b; 45S (2) and 45S+5S (2) adjacent rDNA signals^c	Reddy et al. (2013) ^a-c
	C. naudinianus (syn Acanthosicyos naudinianus)		24^a		Diploid^b; 45S (2) and co-localized 45S+5S (2) rDNA signals^c	Li et al. (2016) ^a,b,c
	C. rehmii		22^a		Diploid^b; 45S (2) and 5S (2) rDNA signals^c	Reddy et al. (2013) ^a-c, Li et al. (2016)^a-c
	C. vulgaris Schrader, 1836		22^a, 44^b	11^c	Diploid^d; 2C: 0.88/0.90pg^e	IPCN ^a,c,d, Arumuganathan and Earle (1991)^e
Coccinia (30)		12^a				Darlington and Janaki Ammal (1945) ^a
	C. abyssinica Lamarck, 1753	12^a	24^b		-	Kumar and Subramaniam (1987) ^a, Roy et al. (1991)^b
	C. grandis	12^a	24^b	12^c	Diploid^d, 2C (Flow cytometry): male- 0.943^e/0.92^f pg and female- 0.849^g/ 0.73^h pg; CSR: 1.33-4.71μm (male) and 1.35-2.26µm (female)ⁱ; 15m+4M+2sm+2m:sm+1m:st (Y) in male and 14m+6M+2sm+2m:st in female^j; NORs-2^k; chromosomal C bands^l; centromeric, nucleolar CMA bands^m; 45S (4)ⁿ rDNA signals, 2 signals adjacent to 5S^o; GISH performed^p; repetitive, organellar DNA hybridized^q; centromere immunofluorescence^r; heteromorphic sex chromosomes (largest Y)^s; X-Y bivalent (meiosis)^t	Bhowmick et al. (2012) ^{b,c,d,j,k,m,s,t}, (2016) ^{b,d,f,h,j,k,n,s}, Sousa et al. (2013)^{b,d,e,g,i,k,l,n,o,r,s,t}, Sousa et al. (2017)^{b,d,k,n,o,p,q,r,s}, Xie et al. (2019a)^b,n,o
	C. hirtella Cogniaux, 1896		24^a		Diploid^b; 2C (flow cytometry): male-0.988pg^c; 45S (4) and 45S+5S (2) adjacent rDNA signals^d, repetitive and organellar DNA hybridized^e; centromere immunofluorescence performed^f	Sousa et al. (2017) ^a-f
	C. sessilifolia Sonder, 1881		24^a		Diploid^b; 2C (Flow cytometry): male- 0.984pg, female- 0.998pg^c; 45S (4) and 45S+5S (2) adjacent rDNA signals^d; repetitive and organellar DNA^e; centromere immunofluorescence performed^f	Li et al. (2016) ^a,b,d, Sousa et al. (2017)^a–f
	C. trilobata		20^a		Diploid^b; 2C (flow cytometry): male- 1.263pg ^c; 45S (2) and 45S+5S (2) adjacent rDNA signals^d, repetitive, organellar DNA sequence hybridized^e	Sousa et al. (2017) ^a-e
Ctenolepis Hooker, 1867	C. garcinii Burman, 1768		24^a	12^b	-	Kumar and Subramaniam (1987) ^a, Beevy and Kuriachan (1996)^b
Diplocyclos Endlicher, 1833	D. palmatus		24^a		Diploid^b; 45S (4) and 45S+5S (2) adjacent rDNA signals^c	Li et al. (2016) ^a-c
Lagenaria Seringe, 1825	L. leucantha Rusby, 1896		22^a	11^b	-	IPCN ^a,b, CCDB^a,b
	L. leucantha var. clavata Makino, 1940		22^a		-	CCDB ^a
	L. siceraria	11^a	22^b	11^c	Diploid^d, 2C (flow cytometry): 0.734pg^e; 2C (Feulgen densitometry):1.4pg^f; CSR: 0.56–1.06μm^g; metacentric and few sub-metacentric chromosomes^h; 45S (2) and 45S+5S (2) adjacent rDNA signalsⁱ	Darlington and Janaki Ammal (1945) ^a, Plant DNA C-Values Database^f, Beevy and Kuriachan (1996)^c, Achigan-Dako et al. (2008)^d,e, Waminal and Kim (2012)^b,d,g,h,i, Li et al. (2016)^b,d,i, Xie et al. (2019a)^b,i
	L. siceraria var. macrocarpa		22^a		-	CCDB ^a
	L. vulgaris Seringe, 1825		22^a	11^b	Diploid^c; 2C (Feulgen densitometry): 1.40pg^d	Bennet et al. (1982)^a,b,c
Melothria		11^a, 12^b				Darlington and Janaki Ammal (1945) ^a,b
	M. pendula Linnaeus, 1753		24^a		Diploid^b; 45S (2) and 45S+5S (2) adjacent rDNA signals^c	Li et al. (2016) ^a-c
	M. perpusilla Blume, 1826		48^a		-	Kumar and Subramaniam (1987) ^a
	M. scabra Naudin, 1866		24^a		-	CCDB ^a
Peponium Engler, 1897	P. betsiliense Keraudren, 1960		24^a		-	CCDB ^a
Solena	S. amplexicaulis Lamarck, 1785 (syn. S. heterophylla, Melothria heterophylla, Zehneria umbellata)		22^a, 24^b, 26^c, 36^d, 48^e	11^f, 12^g, 24^h	2-4 Bⁱ	Kumar and Subramaniam (1987) ^a,b,c,e, Roy et al. (1991)^d,i, Beevy and Kuriachan (1996)^b,g,h, IPCN^b,d,e,f,g,h
Zehneria	Z. capillacea Jeffrey, 1962 (syn. Melothria capillacea)		22^a		-	CCDB ^a
	Z. indica Loureiro, 1790 (syn. Melothria japonica)	11^a	22^b	24^c	Diploid^d; 45S (2) and 45S+5S (2) adjacent rDNA signals^e	Waminal and Kim (2015) ^a,b,d,e
	Z. marlothii Cogniaux, 1962		24^a		Diploid^b; 45S (2) and 45S+5S (2) adjacent rDNA signals^c	Li et al. (2016) ^a,b,c
	Z. maysorensis Wight et Arnott, 1834		48^a	24^b	45S (2) and 5S (2) signals^c	Beevy and Kuriachan (1996) ^a,b, Xie et al. (2019a)^a,c
	Z. mucronata Blume, 1856 (syn. Melothria mucronata)		22^a	12^b	-	Darlington et al. (1956)^a, CCDB^b
	Z. scabra Sonder, 1862 (syn. Melothria punctata)		24^a, 48^b		-	CCDB ^a, Kumar and Subramaniam (1987)^b
	Z. thwaitesii Schweinfurth, 1868		44^a		-	CCDB ^a

Table 7.

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Cytogenetic features of Cucumis (Benincaseae)#.

Species with subspecies/ varieties				Chromosome no.			Ploidy, Genome size, Chromosome features	References
Species with subspecies/ varieties				x	2n	n	Ploidy, Genome size, Chromosome features	References
C. aculeatus Cogniaux, 1895					48^a		Allotetraploid^b; 24II^c	IPCN ^a-c, CCDB^a-c
C. africanus Linnaeus, 1782				12^a	24^b, 48^c	12^d	Diploid^e; 2C (Feulgen microdensitometry): 1.782pg^f; 4 satellited chromosomes^g; 45S (4^h/6ⁱ) rDNA signals, 2 co-localized 45S+5S signals^j	IPCN ^b,c, Yadava et al. (1984)^b,d, Ramachandran and Narayan (1985)^b,e,f, Yagi et al. (2015)^a,b,g,i,j, Zhang et al. (2016)^b,e,h,j
C. angolensis Cogniaux, 1881.					24^a			IPCN ^a
C. anguria Linnaeus, 1753					24^a		Diploid^b; majorly submetacentric and few nearly metacentric chromosomes^c; 1 pair satellited^d; 45S (2) and co-localized 45S+5S (2) rDNA signals^e, ScgCP enables chromosome identification^f; GISH reveals cross species relationships^g	Singh and Roy (1974)^a-d, Zhang et al. (2015)^a,g, (2016)^b,e, Li et al. (2018)^a,f
			C. anguria var. anguria	12^a	24^b	12^c	Diploid^d; 4 satellited chromosomes^e; 45S (2) and co-localized 45S+5S (2) rDNA signals^f	Yadava et al. (1984) ^b,c, Yagi et al. (2015)^a,d,e,f
			C. anguria var. longipes		24^a	12^b	Diploid^c; 2C (Feulgen microdensitometry): 1.587pg^d	Yadava et al. (1984) ^a,b, Ramachandran and Narayan (1985)^a,c,d
			C. anguria var. longaculeatus	12^a	^12.5		Diploid^c; 4 satellited chromosomes^d; 45S (2) and co-localized 45S+5S (2) rDNA signals^e	Yagi et al. (2015) ^a-e
C. asper Cogniaux, 1901					24^a		Diploid^b; 45S (4) and 5S (2) signals detected^c	IPCN ^a, Zhang et al. (2016)^a,b,c
C. callosus Rottler, 1803					14^a, 24^b	12^c	Diploid^d; 2C (Feulgen microdensitometry):1.590pg^e; 11m+1sm (haploid)^f	Ramachandran and Narayan (1985) ^a,d,e, Rajkumari et al. (2013)^b,c, (2015)^b,c,f
C. cinereusCogniaux, 1901 (syn. Cucumella cinerea)							2C (Feulgen microdensitometry): 0.5pg^a	Bennet et al. (1982)^a
C. diniae Raamsdonk et Visser, 1992					48^a		-	IPCN ^a
C. dinteri Cogniaux, 1901					24^a		Diploid^b; 2C (Feulgen microdensitometry): 2.167pg^c	IPCN ^a, Ramachandran and Narayan (1985)^a-c
C. dipsaceus Spach, 1838					24^a	12^b	Diploid^c; 2C (Feulgen microdensitometry): 2.448pg^d; 2m+8sm+2st (haploid)^e; 45S (2) and co-localized 45S+5S (2) rDNA signals^f	Yadava et al. (1984) ^a,b, Ramachandran and Narayan (1985)^a,c,d, Rajkumari et al. (2015)^a,c,e, Zhang et al. (2016)^a,c,f
C. ficifoliusRichard, 1847					24^a, 48^b	12^c	Diploid^d; 2C (Feulgen microdensitometry):1.373pg^e; 45S (2) and co-localized 45S+5S (2) rDNA signals^f	Yadava et al. (1984) ^a,c, Ramachandran and Narayan (1985)^a,d,e, Zhang et al. (2016)^b,f
C. figarei Naudin, 1859					48^a, 72^b		Autoallopolyploid^c; 2C (Feulgen microdensitometry): 3.886pg^e; 36II^f	IPCN ^a-f, Ramachandran and Narayan (1985)^a,c,e
C. heptadactylis Naudin, 1859					48^a	23^b, 24^c, 52^d	Autotetraploid^e; 2C (Feulgen microdensitometry): 2.225pg^f; 8 satellited chromosomes^g; 45S (8) rDNA signals^h of which 4 co-localized to 5S signalsⁱ or separate 5S (4) rDNA signals^j; 10IV+4II^k; irregular meiosis^l	IPCN ^a,e,k, Yadava et al. (1984)^a,b,d,e,l, Ramachandran and Narayan (1985)^a,e,f, Yagi et al. (2015) ^a,e,g,h,i, Zhang et al. (2016)^a,e,h,j
C. hookeri Naudin, 1870					24^a	12^b	Diploid^c	Yadava et al. (1984) ^a,b,c
C. humifructus Stent, 1927					24^a		Diploid^b; 2C (Feulgen microdensitometry): 2.455 pg^c	Ramachandran and Narayan (1985) ^a,b,c
C. hystrix Chakravarty, 1952				12^a	24^b		Diploid^c; 2m+10sm (haploid)^d; 45S (4) and co-localized 45S+5S (2) rDNA signals^e; FISH with bulked oligo probe from cucumber chromosome C7^f, GISH reveals cross species relationships^g	Rajkumari et al. (2015) ^b,c,d, Han et al. (2015)^f, Zhang et al. (2015)^b,g, (2016)^a,b,c,e
C. indicus Ghebretinsae et Thulin, 2007					20^a		Diploid^b; 4m+ 6sm (haploid)^c	Rajkumari et al. (2015) ^a-c
C. javanicus Miquel, 1856 (syn. Melothria assamica)				12^a	24^b, 48^c		-	Kumar and Subramaniam (1987) ^a, CCDB^b,c
C. leiospermus Wight et Arnott, 1834 (syn. Melothria leiosperma)					24^a		-	CCDB ^a
C. leptodermis Schweickerdt, 1933					24^a	12^b	-	Yadava et al. (1984) ^a,b
C. longipes Hooker, 1871					24^a		-	IPCN ^a
C. meeusei Jeffrey, 1965					48^b	22^c, 24^d	Tetraploid^e; 2C- 3.203pg (Feulgen microdensitometry)^f; 45S (6) and co-localized 45S+5S (2) rDNA signals^g	Yadava et al. (1984) ^b,c,d, Ramachandran and Narayan (1985)^b,e,f, Zhang et al. (2016)^b,e,g
C. melo Linnaeus, 1753				12^a	20^b, 22^c, 24^d	12^e	Diploid^f; 2C (Feulgen photometry) : 0.94-1.04pg^g, 1.90pg^h; 2C (Flow cytometry): 1.05pgⁱ; 14m+10st (2SAT)^j; 7m+5sm (haploid)^k; 4 satellites^l or 2 satellites^m; CSR1.0-2.1μmⁿ; CMA bands detected^o; 45S (2) and co-localized 45S+5S (2) rDNA signals^p; centromeric, telomeric, nulceolar and SSR probe hybridization reveals chromosomal relation^q; ScgCP applied for comparative chromosome rearrangement studywith C. sativus^r; FISH with bulked oligo probe from cucumber chromosome C7^s; novel centromeric satellite DNA hybridized on chromosomes^t; GISH reveals cross species relationships^u; infraspecific positional differences in 45S (terminal and interstitial) -5S (terminal, subterminal and interstitial) rDNA signals^v	CCDB ^b,c, Plant DNA C-Values Database^h, Kumar and Subramaniam (1987)^a, Arumuganathan and Earle (1991)^g, Marie and Brown (1993)ⁱ, Zhang (2005)^d,f,j,u, (2015)^d,t, Song and Kim (2008)^d,f,m, Han et al. (2009)^d,e,f,q, (2015)^s, Liu et al. (2010)^d,f,q, Hoshi et al. (2013)^d,f,l,n,o,p, Lou et al. (2014)^r, Rajkumari et al. (2013)^d,e, (2015)^d,f,k, Setiawan et al. (2018)^d,v, (2020)^d,t
			C. melo subsp. melo	12^a	24^b		Diploid; 45S (4) and 5S (2) rDNA signals^c	Zhang et al. (2016) ^a-c
			C. melo subsp. agrestis Naudin, 1859	12^a	24^b		Diploid; 45S (4) and 5S (2) rDNA signals^c	Zhang et al. (2016) ^a-c
			C. melo var. agrestis	12^a	24^b	12^c	Diploid^d; 2C (Feulgen microdensitometry): 2.483pg^e; 10m+2sm (haploid)^f; 1 pair satellited^g	Singh and Roy (1974)^b,d,g, Yadava et al. (1984)^a-d, Ramachandran and Narayan (1985)^b,d,e, Beevy and Kuriachan (1996)^b,c, Rajkumari et al. (2015)^b,d,f
			C. melo var. conomon Thunberg, 1780		24^a		Diploid^b; 7m+3sm+2st (haploid)^c	Zhang et al. (2005) ^a, Rajkumari et al. (2015)^a,b,c
			C. melo var. flexuosus Linnaeus, 1763		24^a		-	IPCN ^a
			C. melo var. inodorus Jacquin, 1832		24^a		Diploid^b; 2C (flow cytometry): 0.64pg^c	Karimzadeh et al. (2010) ^a-c
			C. melo var. melo		24^a	12^b	Diploid^c; 4m+8sm (haploid)^d	Beevy and Kuriachan (1996) ^a,b, Rajkumari et al. (2015)^b,c,d
			C. melo var. momordica Roxburgh, 1832		24^a	12^b	Diploid^c; 2C (Feulgen microdensitometry): 2.291pg^d; 6m+5sm+1st (haploid)^e	Yadava et al. (1984) ^a,b, Ramachandran and Narayan (1985)^a,c,d, Rajkumari et al. (2015)^a,c,e
			C. melo var. muskmelon		24^a	12^b		Yadava et al. (1984) ^a,b
			C. melo var. utilissimus Roxburgh, 1832		24^a	12^b	Diploid^c; 2C (Feulgen densitometry): 2.358 pg^d	Yadava et al. (1984) ^a,b; Ramachandran and Narayan (1985)^a,c,d
C. membranifolius Hooker, 1871					48^a	24^b	-	Yadava et al. (1984) ^a,b
C. metulifer Naudin, 1859 (syn. C. metuliferus)					24^a	12^b	Diploid^c; 2C (Feulgen microdensitometry): 2.391pg^d; metacentric, submetacentric, subtelocentric chromosomes^e; CSR: 0.9–2.0 μmf; 4 satellites^g; nucleolar and centromeric CMA-DAPI bands^h; 45S (2) and co-localized 45S+5S (2) rDNA signalsⁱ, satellite sequences^j and telomeric DNA^k hybridized on chromosomes; ScgCP applied for comparative chromosome rearrangement studywith C. sativus^l; GISH reveals cross species relationships^m	Yadava et al. (1984) ^a,b,c, Ramachandran and Narayan (1985)^a,c,g, Ramachandran and Narayan (1990)^a,c,i, Hoshi et al. (2013)^a,c,e,f,g,h, Lou et al. (2014)^l, Yagi et al. (2014)^{a,c,g,h,i,j,k}, Li et al. (2016)^a,c,i, Zhang et al. (2015)^a,m, (2016)^a,c,i
C. myriocarpus					24^a	12^b	Diploid^c; 45S (2^d/4^e) and co-localized 45S+5S (2)^f rDNA signals^d	CCDB ^a; Zhang et al. (2016)^a,b,c,d,f, Yagi et al. (2015)^a-f
			C. myriocarpus subsp. leptodermis Schweickerdt, 1933	12^a	24^b		Diploid^c; 4 satellited chromosomes^d; 45S (3^e, 2^f) and co-localized 45S+5S (2^g) rDNA signals	Yagi et al. (2015) ^a-g
			C. myriocarpus var. myriocarpus	12^a	48^b		Tetraploid^c; 8 satellited chromosomes^d; 45S (4) and co-localized 45S+5S (4) rDNA signals^e	Yagi et al. (2015) ^a-e
C. prophetarum Linnaeus, 1755					24^a	12^b	Diploid^c, 2C (Feulgen Microdensitometry): 1.656 pg^d 5m+7sm (haploid)^e	Ramachandran and Narayan (1985) ^a,c,d, Rajkumari et al. (2013)^a,b, (2015)^a,c,e
	C. prophetarum subsp. zeyheri Sonder, 1862				48^a		-	IPCN ^a
C. pubescens Willdenow, 1805					24^a	12^b	-	IPCN ^a; Beevy and Kuriachan (1996)^b
C. pustulatus Hooker, 1871					48^a, 72^b	24^c	Hexaploid^d, 45S (8) and co-localized 45S+5S (2) rDNA signals^e; FISH with bulked oligo probe from cucumber chromosome C7^f	Yadava et al. (1984) ^a,c, Han et al. (2015)^f, Zhang et al. (2016)^b,d,e
C. ritchiei Clarke, 1879					24^a		Diploid^b, 8m+4sm (haploid)^c	Rajkumari et al. (2015) ^a,b,c
C. sagittatus Peyritsch, 1860					24^a	12^b	Diploid^c, 2C (Feulgen microdensitometry):1.571pg^d	Yadava et al. (1984) ^a,b, Ramachandran and Narayan (1985)^a,c,d
C. sativus Linnaeus, 1753				7^a	14^b	7^c	Diploid^d, 2C (flow cytometry): 1.03pg^e /1.77pg^f; 12 metacentric and 2 sub-metacentric chromosomes^g; CSR: 0.83-1.01μm^h, chromosomal C-bandsⁱ; centromeric 45S (10) and distal 5S (2) rDNA signals^j; FISH with centromeric and telomeric^k and SSR probe reveals chromosome evolution^l; high resolution molecular cytogenetic map^m; ScgCP applied for cross species chromosome rearrangement studyⁿ; FISH with bulked oligo probe from cucumber chromosome C7 in comparison with 5 Cucumis species^o; GISH reveals cross species relationships^p	Kumar and Subramaniam (1987) ^a,b, Marie and Brown (1993)^f, Beevy and Kuriachan (1996)^b,c, Hoshi et al.(2008)^b,d,i, Barow and Meister (2003)^b,d,e, Han et al (2011)^b,d,k,l,m, Liu et al. (2010)^b,l, Waminal and Kim (2012)^b,d,g,h,j, Rajkumari et al. (2013)^b,c,f, Sun et al. (2013)^b,m, Lou et al. (2014)^b,n, Han et al. (2015)^o, Zhang et al. (2015)^b,p, Li et al. (2016)^b,d,j
		C. sativus var. Hokutosei		7^a	14^b		Diploid^c, 12 metacentric, 2 sub-metacentric chromosomes^d; centromeric and telomeric signals^e	Zhang et al. (2012) ^a-e
		C. sativus var. hardwickii Royle, 1835		7^a	14^b		Diploid^c; 2C (Feulgen Microdensitometry): 1.798pg^d; 6m+1sm (haploid)^e; centromeric 45S (6) and intercalary 5S (2) rDNA signals^f, centromeric, telomeric and SSR probe hybridization^gh; molecular cytogenetic mapⁱ	Ramachandran and Narayan (1985) ^b,d, Zhao et al. (2011)^b,c,f,g, Yang et al. (2012)^b,h, Rajkumari et al. (2015)^b,c,e, Zhang et al. (2016)^a,b,c,f
		C. sativus var. hardwickii Royle, 1835		7^a	14^b
		C. sativus var. Long green		7^a	14^b		Diploid^c, 12 metacentric, 2 sub-metacentric chromosomes^d; centromeric and telomeric sequence signals^e	Zhang et al. (2012) ^a-e
		C. sativus var. sativus (CSS)		7^a	14^b		Diploid^c, centromeric 45S (10) and intercalary 5S (2) rDNA signals^d; centromeric and distal repetitive sequence probes^e; molecular cytogenetic map^f	Zhao et al. (2011) ^b-e, Yang et al. (2012)^b,f, Zhang et al. (2016)^a-d
		C. sativus cv. Winter Long			14^a	7^b	Diploid^c, C- banding^d, DAPI banding^e, 45S (6) and 5 S (2) rDNA signals^f, repetitive sequence based molecular karyotype in somatic and pachytene chromosomes^g	Koo et al. (2002) ^a-f, (2005)^a,b,g
		C. sativus var. xishuangbannesis Qi et Yuan Zhenzhen, 1983		7^a	14^b		Diploid^c, centromeric 45S (10) and intercalary 5S (2) rDNA signals^d; centromeric and telomeric signals^e	Zhao et al. (2011) ^b,c,e, Zhang et al. (2016)^a-d
C. setosus Cogniaux, 1881					24^a	12^b	Diploid^c; 4m+5sm+3st (haploid)^d	Rajkumari et al. (2013) ^a-c, (2015)^a,c,d
C. silentvalleyii Manilal et Sabu et Mathew, 1985					24^a	12^b	-	Rajkumari et al. (2013) ^a,b
C. trigonus Roxb.					24^a	12^b	-	Rajkumari et al. (2013) ^a,b
C. zambianus Widrl., J.H.Kirkbr., Ghebret. and K.R.Reitsma				12^a	24^b		Diploid^c; 45S (2) and co-localized 45S+5S (2) signals^d	Zhang et al. (2016) ^a-d
C. zeyheri Sond.					24^a, 48^b		Diploid^c, Allotetraploid^d; 2C (Feulgen densitometry): 1.682^e/2.846 pg^f; 4 satellites^g; 45S (2) and co-localized 45S+5S (2) rDNA signals^h; FISH with bulked oligo probe from cucumber schromosome C7ⁱ; 24II^j , 12II^k, 11II+2I^l	IPCN ^a,b,d,j,k,l, Ramachandran and Narayan (1985)^a-f, Han et al. (2015)ⁱ, Yagi et al. (2015)^a,c,g,h
Cucumella cinerea (Cogn.) C.Jeffrey							2C (Feulgen Microdensitometry): 0.50pg^a	Bennet et al. (1982)^a
Mukia maderaspatana (L.) M.Roem. (syn. Cucumis maderaspatanas and Melothria maderaspatana)				12^a	24^b	11^c, 12^d	-	CCDB ^b,c, Rajkumari et al. (2015)^b,d
Oreosyce africana Hook.f. (syn. Cucumis subsericeus)				12^a	48^b		Tetraploid^c; co-localized 45S and 5S rDNA signals (2)^d; FISH with bulked oligo probe from cucumber chromosome C7^e	Han et al. (2015) ^e, Zhang et al. (2016)^a-d

Table 8.

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Cytogenetic information in Cucurbiteae #.

Genera studied	Species studied	Chromosome no.			Ploidy, Genome size, Chromosome features	References
Genera studied	Species studied	x	2n	n	Ploidy, Genome size, Chromosome features	References
Cayaponia Silva Manso, 1836	C. laciniosa Linnaeus, 1753		24^a		-	Kumar and Subramaniam (1987) ^a
Cucurbita		10^a, 12^b			-	Darlington and Janaki Ammal (1945) ^a,b
	C. andreana Naudin, 1896		40^a			CCDB ^a
	C. argyrosperma Huber, 1867 (syn. C. mixta Pangalo, 1930)		40^a		2C (flow cytometry): 0.748 pg^b	Sisko et al. (2003)^a,b
	C. cylindrata Bailey, 1943		40^a	20^b	-	CCDB ^a,b
	C. digitata Gray, 1853	10^a, 12^b	40^c	20^d	-	Darlington and Janaki Ammal (1945) ^a,b, CCDB^c,d
	C. ecuadorensis Cutler et Whitaker, 1969				2C: 0.72pg^a	Plant DNA C Value database^a
	C. ficifolia Bouché, 1837 (syn. C. melanosperma Gasparrini, 1847)		40^a		2C (flow cytometry): 0.933pg^b	Plant DNA C- Values Database^a,b
	C. foetidissima Kunth, 1817	10^a, 12^b	40^c, 42^d		2C (flow cytometry): 0.686pg^e	Darlington and Janaki Ammal (1945) ^a,b, Plant DNA C- Values Database^c,e, CCDB^c,d
	C. indica (unresolved)		40^a		-	IPCN ^a
	C. lundelliana Bailey, 1943			20^a	2C (flow cytometry): 0.72pg^b	CCDB ^a, Plant DNA C Value database^b
	C. maxima Duchesne, 1786	20^a	24^b, 40^c, 44^d, 48^e	20^f		Kumar and Subramaniam (1987) ^a,c,d,e, Beevy and Kuriachan (1996)^f, CCDB^c,f
	C. moschata Duchesne, 1786	10^a, 12^b	24^c, 40^d, 44^e,48^f		Diploid^g; 2C (Feulgen microdensitometry): 0.90pg^h; 2C (flow cytometry): 0.708ⁱ/ 0.97^jpg; 36 metacentric and 4 sub-metacentric chromosomes^k; CSR: 1.05-1.78μm^l, 45S (10) and 5S (4) rDNA signals^m	CCDB ^f, Plant DNA C- Values Database^h,i, Kumar and Subramaniam (1987)^a-f, Barrow and Meister (2003)^j, Xu et al. (2007)^d,m, Waminal et al. (2011)^g,d,k,l,m
	C. okeechobeensis ssp. martinezii Bailey, 1943		40^a		2C (flow cytometry): 0.74pg^b	Plant DNA C- Values Database^a,b
	C. palmata Watson, 1876	10^a, 12^b	40^c, 42^d	20^e	-	Kumar and Subramaniam (1987) ^a,b, CCDB^c,d,e
	C. pedatifolia Bailey, 1943		40^a		-	CCDB ^a
	C. pepo Linnaeus, 1753	10^a, 12^b	22^c, 24^d, 28^e, 40^f, 42^g, 44^h, 46ⁱ, 80^j	20^k	2C (flow cytometry): 0.74pg^l; 0.864^m; 1.109 pg-1.064 pgⁿ; 1.18pg^o; 45S (10) and 5S (4) rDNA signals^p	Kumar and Subramaniam (1987) ^a-j, CCDB^f,k, Marie and Brown (1993)^l, Barow and Meister (2003)^o, Rayburn (2008)ⁿ, Plant DNA C- Values Database^m, Xie et al. (2019b)^{f, p}
Sicana Naudin, 1862	S. odorifera Vellozo, 1831		40^a	20^b	-	IPCN ^a,b

Nuclear genome contents

Nuclear genome sizes are reported in 49 species (~5% of total species) belonging to 15 genera (~16% of total genera) of Cucurbitaceae. Among the understudied tribes, 2C genome content is known for one species each from Gomphogyneae and Coniandreae (Table 2). Within the Momordiceae species of India, significant interspecific genome size differences have been reported (Ghosh et al. 2021). The species differed 5.19-fold in their genome sizes (2C = 0.72-3.74 pg) (Table 3) (Ghosh et al. 2021). Interestingly, the species with lowest chromosome number (M. cymbalaria, 2n = 18) contained highest nuclear DNA content among the four Momordica species (Table 3). In Bryonieae, flow cytometric genome size of Bryonia shows a 2.2-fold increase than Ecballium (Table 4). In case of Sicyoeae, flow cytometric 2C DNA content ranges from 1.49–2.32 pg/2C, indicating 1.55-fold differences in genome size. Echinocystis lobata Michaux, 1803, in spite of tetraploid condition, shows lowest genome size (Table 5). There is no significant difference in genome size between the genders of Trichosanthes dioica Roxburgh, 1832 (Table 5). Genome size estimates are known from 24 Benincaseae species of which 17 species belong to Cucumis (Tables 6, 7). Highest 2C nuclear genome is known in Benincasa hispida Thunberg, 1784 (1.97 pg) (Bhowmick and Jha 2015a) while the lowest is known in Cucumis melo var. inodorus Harz, 1885 (0.64 pg) (Karimzadeh et al. 2010). In case of Cucumis, there is yet no consensus on whether the taxa with different base numbers (x = 7, 12) have correspondingly dissimilar genome sizes since the researchers depended on diverse methods of genome size estimation. Lower 2C genome size was reported in C. Coccinia grandis Linnaeus, 1767 (2n = 24) while C. trilobata (2n = 20) had higher 2C DNA content (Table 6). The divergence in genome size between genders was found to be highest in dioecious C. grandis (Table 6), a sharp contrast to dioecious Trichosanthes dioica (Table 5). Benincaseae shows a 3.07-fold overall difference in genome size. Genome sizes are known in eight species of Cucurbita Jussieu, 1789. Flow cytometric genome size ranges from 0.686–0.933 pg/2C, indicating a 1.36-fold variation (Table 8). Despite polypoidy, the nuclear DNA content of Cucurbita species is comparable to many diploids.

Karyotypes, chromosome banding and molecular cytogenetics

Among the understudied tribes, information on chromosome morphology, size and karyotype are reported in very few taxa (Table 2). In Gynostemma pentaphyllum Thunberg, 1784, the number of rDNA loci was suggested to reduce during polyploidization (Pellerin et al. 2018). The Actinostemma tenerum Griffith, 1837, genome contained interstitial telomeric repeats which were suggested to be the result of chromosome fusion from ancestral genome. The co-localization of 45S and 5S rDNA loci in A. tenerum and Thladiantha dubia Bunge, 1833, have been thought to imply regional synteny and shared ancestral traits (Xie et al. 2019b). In the tribe Cucurbiteae, detailed karyotype analysis is known only in Cucurbita moschata Duchesne, 1786 and C. pepo Linnaeus, 1753, showing conserved 45S and 5S rDNA signals (non-co-localized) in independent analyses (Table 8).

Karyotypes and chromosome sizes are reported in ten species of Momordiceae (Table 3). Interspecific differences have been observed and found to correlate with phylogenetic relationship within Momordica (Ghosh et al. 2021). Infraspecific delimitation of Indian M. charantia varieties was based on fluorochrome banding pattern and genome size divergence (Table 3), corresponding to infraspecific distinction reported in the Japanese bitter gourd cultivars (Kido et al. 2016). FISH in three Momordica species revealed 45S and 5S rDNA sites to be localised on different chromosomes (Table 3). In context of the genome sequence of bitter gourds (Matsumura et al. 2020), further scopes for cytogenetic and genomic investigation remain open.

Karyotype and chromosome size is reported in eight 8 species of Sicyoeae (Table 5). Fluorochrome banding pattern has facilitated comparative analysis in Luffa species occurring in India (Tables 1, 5) (Bhowmick and Jha 2015a, 2021). The cultivated ridged gourd (L. acutangula Linnaeus, 1753) showed three CMA⁺ satellite bearing pairs (Fig. 1A–C, J) as in the wild L. echinata Roxburgh, 1814 (Fig. 1G–I, L), while the sponge gourd (L. aegyptiaca Miller, 1768 has two satellited pairs (Fig. 1D–F, K). Luffa acutangula and L. echinata also showed up distal DAPI bands (Fig. 1J, L), absent in L. aegyptiaca (Fig. 1K). Trichosanthes species (2n = 22) have inter-specific differences (Fig. 2) as well as infraspecific distinction (T. cucumerina Linnaeus, 1753) in fluorochrome banding pattern (Tables 1, 5, Fig. 2A–H). The male and female plants of T. dioica show similar chromosome number, morphology and genome size but show differences in fluorochrome banding pattern (Fig. 2I–P, Table 5). The 11^th, 12^th and 13^th pairs (CMA⁺) are marker chromosomes in Luffa (Fig. 1, Table 1) while the 10^th and 11^th pairs are conserved CMA⁺ satellited pairs in Trichosanthes (Fig. 2, Table 1). Eight species of Sicyoeae have been subjected to FISH (Table 5). The polyploid and diploid species have differences in the number of rDNA loci, showing separate localization of the 45S and 5S rDNA signals except Sicyos angulatus Linnaeus, 1753 and Trichosanthes kirilowii Maximowicz, 1859 (Table 5).

Benincaseae generally reveal two distal 45S rDNA loci of which at least one locus is either adjacent to 5S rDNA locus (Table 6) or co-localized in the same chromosome as in most of the Cucumis species (Table 7). Exceptionally, a wild species of Benincasa (B. fistulosa Stocks, 1851) has non-adjacent 45S and 5S signals (Li et al. 2016). GC rich satellites were observed in the 12^th pair of chromosomes showing CMA⁺ bands in cultivated Indian ashgourd (B. hispida) (Fig. 3 A–C, J, Tables 1, 6). Lagenaria siceraria Molina, 1782 and Cucumis melo Linnaeus, 1753 are the other two genera having similarity in rDNA hybridization profile, agreeing with phylogenetic affinity (Li et al. 2016).

Citrullus colocynthis Linnaeus, 1753 and C. lanatus Thunberg, 1794 may share a common ancestor both having two 45S rDNA loci and one 5S locus. Loss of one 45S rDNA locus has given way to C. rehmii De Winter, 1990 while gain of one 5S rDNA locus has been proposed to lead to C. ecirrhosus Cogniaux, 1888 and C. lanatus var. citroides Bailey, 1930 (presently C. amarus Schrader, 1836) (Reddy et al. 2013; Li et al. 2016). GISH using C. lanatus var. citroides genome has revealed divergence from C. lanatus var. lanatus (Reddy et al. 2013).

The genus Cucumis is the largest in Benincaseae with 65 species of which 39 have been studied (Table 7). Among the Cucumis species with x = 12, co-localization rDNA loci (45S and 5S rDNA) have been documented in 14 species, including C. melo (Table 7). However, the number of 45S sites is generally four, which may be six or eight in some cases (Table 7). rDNA hybridization data strongly corroborated with the ‘fusion’ theory for derivation of x = 7 (C. sativus) from x = 12 (C. melo) (Waminal and Kim 2012) which is substantiated by genomic studies (Li et al. 2011). There are ten pericentromeric/ centromeric 45S and two distal 5S rDNA sites in C. sativus while six 45S rDNA sites were reported in C. sativus var. hardwickii Royle, 1835 (Koo et al. 2005; Zhang et al. 2012). Comparative chromosome painting (Lou et al. 2014) and GISH (Zhang et al. 2015) proved high colinearity between cucumber and melon. Based on chloroplast and nuclear DNA (ITS) phylogeny, C. melo (melon) has been found to be sister to a clade comprising C. sativus and related genera (Dicaelospermum Clarke, 1879 and Mukia Arnott, 1840) (Renner et al. 2007). rDNA site co-localization was found to coincide with geographical origin of 12 Cucumis species (Zhang et al. 2016). The chromosomal affinity between C. metuliferus Schrader, 1838, C. anguira Linnaeus, 1753, C. zeyheri Sonder, 1862, C. myriocarpus Naudin, 1859 and polyploid C. heptadactylis Naudin, 1859 (dioecious) (Yagi et al. 2015) can be substantiated by their phylogenetic proximity based on chloroplast and nuclear DNA (ITS) sequences (Renner et al. 2007). rDNA distribution of C. metuliferus was also the reason to consider proximity with Citrullus naudinianus Sonder, 1862, (previously Acanthosicyos naudinianus Sonder, 1862) (Reddy et al. 2013). Infraspecific differences were documented in Cucumis melo on the basis of 45S- 5S rDNA signals (linked or separated) which also possessed unique centromeric satellites (Setiawan et al. 2018, 2020). Moreover, chromosome painting method elucidated chromosomal rearrangement in some Cucumis species (Lou et al. 2014; Li et al. 2018).

The dramatic evolution of Y chromosome was validated in karyotypes (Fig. 3 D–I, K–L) of Coccinia grandis (Table 6). The 45S rDNA sites enabled confirmation of NORs in the 8^th and 12^th pair containing distal GC rich CMA⁺ signals in C. grandis (Fig. 3 D–I, K–L, Tables 1, 6). 45S and 5S rDNA hybridization pattern was similar in three other Coccinia species and Diplocyclos palmatus Linnaeus, 1753 (Table 6). The three closely related dioecious species of Coccinia accumulated Y chromosome repeats and displayed sex chromosome turnover (Sousa et al. 2017). Strong centromeric CMA bands (Fig. 3 D–I, K–L, Table 1) were observed in C. grandis except Y chromosome (Fig. 3 I, L), presenting a possibility that CgCent (CL1) is a feature of centromeres of dioecious Coccinia species (Sousa et al. 2017). In addition, non-nucleolar CMA⁺ heterochromatin might be associated with sexual differentiation of autosomes in dioecious C. grandis (Fig. 3) which is also a marker in Trichosanthes dioica (Fig. 2, Table 1), opening good scope for further study.

Distinct 45S rDNA sites are higher in number than 5S rDNA sites in Cucurbitaceae (Fig. 4) (Waminal and Kim 2012). The distal 45S rDNA loci are conserved genomic landmarks (Fig. 4) while 5S rDNA loci are relatively diverse (Fig. 4). Based on the literature reports, some NORs (Type I) included chromosomes showing non-colocalized 45S and 5S rDNA sites in seven species of Benincaseae, one species each from Cucurbiteae and Momordiceae and two species of Sicyoeae. The rearrangement of 45S rDNA site in Cucumis sativus, probes for chromosome number reduction which may be a consequence of diploidization. The second type (Type II) shows colocalised 45S and 5S rDNA loci, either adjacent or distant, but always on the same chromosome and found in one species each of Benincaseae, Sicyoeae and Actinostemmateae. The third type (Type III) was characterized by chromosomes with non-colocalized and colocalised 45S and 5S rDNA loci, as in 14 species of Benincaseae and one species each of Sicyoeae and Thladiantheae. The rDNA sites of majority of Cucumis species were of non-adjacent type. Hence, type III NORs in majority of Benincaseae genera advocates conservation of the marker chromosomes having distal NOR (45S rDNA). Gynostemma pentaphyllum and some polyploid Cucumis reveal rDNA loci reduction after polyploidization (Zhang et al. 2016; Pellerin et al. 2018).

Figure 4.

Types of chromosomes bearing the NORs as per available reports of rDNA hybridization in Cucurbitaceae. Type I: Chromosomes with only non-colocalised 45S and 5S rDNA sites, Type II: Chromosomes with colocalised 45S and 5S rDNA sites, Type III: Chromosomes with both non- colocalised and colocalised 45S and 5S rDNA sites. See text for explanation.

Correlation between parameters

Chromsome numbers in Cucurbitaceae range from x = 5 to x = 16. The most prevalent number x = 12 (Fig. 5) is considered ancestral (Xie et al. 2019b), followed by x = 11, 13, 14 and 10 (Fig. 5). The present regression analyses for 41 taxa (including 16 Indian taxa) (Table 9) revealed significant linear correlation between 2n and HCL, between ploidy and genome size and between ploidy and HCL (Fig. 6). Therefore, an increase in ploidy/ 2n number is linked with increase in HCL. There was no significant correlation between 2C genome size and chromosome numbers. Cytogenetic parameters may not reflect residual evidence of CCT in Cucurbitraceae at present, as reasoned by Alix et al. (2017).

Table 9.

Download as

CSV

XLSX

Data on fundamental cytogenetic parameters utilized for statistical analysis.

Species	2n Chromosome no.	Ploidy	2C genome size (pg)	MCL (μm)	HCL (μm)	References
Gynostemma pentaphyllum	66	6	3.62			Zhang et al. (2013), Pellerin et al. (2018)
Zanonia indica	30	2		1.47	22.12	Lekhak et al. (2018)
Momordica balsamina	22	2		1.30	14.3#	Bharathi et al. (2011)
Momordica charantia var. charantia	22	2	0.72	1.97	21.77	Ghosh et al. (2018)
Momordica charantia var. muricata	22	2	1.16	2.19	24.19	Ghosh et al. (2018)
Momordica cochinchinensis	28	2	2.64	2.27	31.86	Ghosh et al. (2021)
Momordica cymbalaria	18	2	3.74	3.75	33.79	Ghosh et al. (2021)
Momordica dioica	56	4	3.36	2.75	77.1	Ghosh et al. (2021)
Momordica sahyadrica	28	2		1.34	18.76	Bharathi et al. (2011)
Momordica subangulata	56	4	3.06	2.15	60.3	Ghosh et al. (2021)
Luffa acutangula	26	2		2.20	28.63	this study
Luffa cylindrica	26	2	1.56	2.98	38.77	Bhowmick and Jha (2015a), this study
Luffa echinata	26	2		3.17	41.26	this study
Trichosanthes cucumerina	22	2		3.47	37.855	Bhowmick and Jha (2019), this study
Trichosanthes cucumerina subsp. cucumerina Anguina	22	2		3.43	37.74	Bhowmick and Jha (2019), this study
Trichosanthes dioica Male	22	2	2.27	3.71	40.82	Bhowmick and Jha (2015a), this study
Trichosanthes dioica Female	22	2	2.32	3.71	40.82	Bhowmick and Jha (2015a), this study
Benincasa hispida	24	2	1.97	3.17	38.08	Bhowmick and Jha (2015a), this study
Citrullus lanatus	22	2		1.33#	14.67	Waminal et al. (2011)
Coccinia grandis male	24	2	0.92	1.80	20.32	Bhowmick et al. (2012, 2016), this study
Coccinia grandis female	24	2	0.73	1.86	19.85	Bhowmick et al. (2012, 2016), this study
Coccinia hirtella	24	2	0.988			Sousa et al. (2017)
Coccinia sessilifolia Male	24	2	0.984			Sousa et al. (2017)
Coccinia sessilifolia Female	24	2	0.998			Sousa et al. (2017)
Coccinia trilobata	20	2	1.263			Sousa et al. (2017)
Lagenaria siceraria	22	2	0.734	1.79	20.06	Achigan-Dako et al. (2008)
Cucumis africanus	24	2		2.08	25.045	Yagi et al. (2015)
Cucumis anguria var. anguria	24	2		2.13	25.6	Yagi et al. (2015)
Cucumis anguria var. longaculeatus	24	2		2.10	25.195	Yagi et al. (2015)
Cucumis heptadactylus	48	4		2.09	50.225	Yagi et al. (2015)
Cucumis melo	24	2	1.05	1.50	17.8#	Marie and Brown (1993), Hoshi et al. (2013)
Cucumis melo var. inodorus	24	2	0.64			Karimzadeh et al. (2010)
Cucumis myriocarpus var. leptodermis	24	2		1.93	23.19	Yagi et al. (2015)
Cucumis myriocarpus var. myriocarpus	48	4		2.25	53.985	Yagi et al. (2015)
Cucumis zeyheri	24	2		2.30	27.56	Yagi et al. (2015)
Cucumis sativus	14	2	1.03, 1.77##	2.07#	14.50	Barow and Meister (2003), Marie and Brown (1993), Waminal and Kim (2012)
Cucurbita argyrosperma	40		0.748			Roy et al. (1991), Sisko et al. (2003)
Cucurbita ecuadorensis	40		0.933			Sisko et al. (2003)
Cucurbita foetidissima	40		0.686			Sisko et al. (2003)
Cucurbita moschata	40	2	0.708, 0.97##	1.26#	25.19	Sisko et al. (2003), Barrow and Meister (2003), Waminal et al. (2011)
Cucurbita okeechobeensis ssp. martinezii	40		0.74			Sisko et al. (2003)

Figure 5.

The types of different base numbers (x, based on published reports) or possible base numbers (x/n, based on reported haploid counts) in Cucurbitaceae. The numbers in brackets beside names of genera signify the number of species whose chromosome counts are reported. The % of genera and species with a particular chromosome number, is indicated at the end arrow (out of a total of 44 genera and 188 species with chromosome counts).

Figure 6.

Scatter plots of 2n chromosome number and ploidy level (predictor variables) versus 2C genome size, MCL (mean chromosome length) and HCL (total length of haploid chromosome set) in Cucurbitaceae taxa. Symbols below plots depict regression analysis parameters; square: adjusted R square, circle: standard error of the estimate, triangle: Pearson Correlation, star: 2-tailed significance of Pearson Correlation. Regular lines indicate significant linear regression and dotted lines indicate not significant linear regress

Future directions

Chromosome number and genome size information in the basal clades (understudied tribes) should be given attention to infer ancient base numbers. The parameters of fundamental and molecular cytogenetics are inevitable for genomic interpretation (Weiss-Schneeweiss and Schneeweiss 2013; Deakin et al. 2019) and hence relevant to spot genetic resources and relationships with wild relatives. The current review is not exhaustive but supersedes the scopes of general web resources and brings an offline resource exclusive for Cucurbitaceae.

Acknowledgements

SJ is thankful to the National Academy of Sciences (NASI, Allahabad, India) for the NASI Senior Scientist Fellowship award. BKB gratefully acknowledges Principal, Scottish Church College, India for continuous support and encouragement in research activities.

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ORCID

Biplab Kumar Bhowmick https://orcid.org/0000-0001-6029-1098

Sumita Jha https://orcid.org/0000-0002-1375-2768

﻿Abstract

Keywords

﻿Introduction

﻿Methodological approaches

﻿Data compilation

﻿Chromosome analysis in the Cucurbit species ocurring in India

﻿Statistical analyses

﻿The modern cytogenetic catalogue of cucurbitaceae

﻿Chromosome numbers

﻿Nuclear genome contents

﻿Karyotypes, chromosome banding and molecular cytogenetics

﻿Correlation between parameters

﻿Future directions

﻿Acknowledgements

﻿References

﻿ORCID

Abstract

Introduction

Methodological approaches

Data compilation

Chromosome analysis in the Cucurbit species ocurring in India

Statistical analyses

The modern cytogenetic catalogue of cucurbitaceae

Chromosome numbers

Nuclear genome contents

Karyotypes, chromosome banding and molecular cytogenetics

Correlation between parameters

Future directions

Acknowledgements

References

ORCID