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Cucurbit Genetics Cooperative Report 17:61-65 (article 16) 1994

Chromosome Number and Karyotype of Melons (Cucumis melo L.)

Dewei Ma, Zhenhuai Guo. Chenghe Zhang, and Souzhu Gao; Ming Wang

Hebei Agricultural University, Boading, Hebei, CHINA; Northwestern Agricultural University, Yangling, Shaanxi, CHINA

The number of chromosomes in 36 melon cultigens was identified and the karyotypes of two typical melon cultivars were analysed by the improved cytological method. The results were shown as follows: 1) all of the materials identified, except a tetraploid strain with 48 chromosomes (4n=48) in somatic cells, are normal diploid (2n=24); 2) the karyotypes of an America muskmelon (Cucumis melo var. reticulatus) and "Hetain" (Cucumis melo spp. melo Pang) could be described as: 2n=2x=24=18m+2sm+2sm (SAT) and 2n=2x=24=18m+4M+2sm, respectively. Both karyotypes showed better symmetry which belong to 2A and 1S type, respectively.

In China, melon (Cucumis melo, L.) is an important horticultural crop and the germplasm resources are very rich and have a long growing history. In the world, there are more than 3000 cultivars and forms which belong to 8 variety groups. However, because of the heavy plasm and small chromosomes in melon cells, it is quite difficult to stain the chromosome and to identify the morphological characteristics of the chromosomes. So far, the reports on melon chromosomes have been extremely rare. In this paper, some characteristics of melon chromosomes were studied which would be of significance in melon breeding classification, evolution, etc.

Newly developed root tips or shoot apices from each of melon cultigens were used. Chromosomes were identified by the improved cytological method of Zhasng Zili (1977). Thirty metaphase somatic cells from each of the materials were selected and the number of chromosomes in each of cells was determined. The karyotypes of two typical cultivars, American Muskmelon (Cucumis melo var. reticulatus) and "Hetian," (C. melo spp. melo Pang.) were analysed according to the chromosome classification and nomenclature method of Leven, 1964,

Number of chromosomes and ploidy in each of 36 melon materials. The results are shown in Table 1. Among all of the 36 melon cultigens, 32 (numbers 1-32), including cultivars, hemi-wild species and wild species from various regions of the world, are normal diploid with a common number of chromosomes (2n=2x=24) in spite of remarkable differences in the origin and habits; 3 (numbers 33-35) are mixoploid, i.e., many diploid somatic cells are mixed with few tetraploid cells in same material; and only 1 (number 36) is an artificial tetraploid melon strain (4n=4x=48).

Chromosome shape and karyotypes. Two typical cultigens, America Reticulatus and Hetian, were used as the materials for karyotype analysis. The length and arm ratio of chromosome in America Reticulatus are shown in Table 2. The absolute length of chromosomes at metaphase ranged from 1.65 to 1.18 with the relative length ranging from 10.02 to 7.13 %m. Ratio of the longest chromosome to the shortest one is 1.4. The mean length of 12 chromosomes is 1.37 m. Chromosomes 1, 2, 4, 5, 7, 8, 9, 10, 11, and 12 belong to metacentric chromosome (m) with their arm ratios ranging from 1.08 to 1.52. Chromosome 3 belongs to submetacentric chromosome (sm) with its arm ratio being 2.17. Chromosome 6 with a larger satellite on the short arm belongs to sub-metacentric SAT chromosome with its arm ratio being 1.84. Considering the morphological characteristics and the arm ratios, all of the 12 pairs of chromosomes could be distinguished clearly at metaphase as shown in Fig. 1. The chromosomes were arranged in descending order of the length and the karyotype formula can be expressed as: 2n=2x=24=20m=2sm (SAT), which belong to 2A type.

Melon karyotype nd its position in Cucurbitaceae. The results in this study showed that the melon karyotypes belong to 1A or 2A types. A better symmetry of chromosomes was found as compared with that in cucumber (1A), gourd (1A), sponge gourd (1A), balsampear (2A, 1B), watermelon (2A), white gourd (2A), Chinese squash (2A), Indian squash (2A), American squash (2B), chayote (2B), and snake gourd (2A), (Ronquian Li, 1989). According to Stebbins' (1971) theory concerning plant karyotype evolution, we could deduce that melon belongs to species of a lower evolutive degree in Cucurbitaceae on the basis of the karyotypes mentioned, while the cucumber, gourd and sponge gourd etc., belong to the very old crop type in evolution.

Morphological characteristics of the chromosomes in melon. Chromosomes in melons have the following main feature: 1) the range of chromosome length is narrow; 2) chromosomes are mainly metacentric or submetacentric with a better symmetry; 3) the size of chromosomes is small, shorter than 2m in length and melons belong to the crops with the smallest chromosomes in Cucurbitaceae plants; 4) secondary constriction not recognized.

Karyotype variation in melons. Although the number and shape of the chromosomes are the same or similar in different melon species, some differences exist, such as chromosome size and karyotype, etc. These differences revealed a certain variation in chromosome structure in melon plants. Similar phenomena were discovered in garlic (Verna, 1978) Senvy, tomato, cucumber, pepo and white gourd (Rongquian Li, 1989). So far, no satisfactory explanation from genetic aspect has been provided and further investigations are needed.

In the experiment, a few tetraploid cells in a couple of diploid melon materials were observed. We consider that the origin of the tetraploid cell might be: 1) the number of chromosomes in few cells was doubled during the treatment with chemicals; 2) the tetraploid cells were induced to be doubled spontaneously.

Table 1. Number of chromosomes in somatic cell.

Order Number
Name
Origin
Variety
Number of Chromosomes
1
Hongxin melon
Liaoning, China
makuwa
24
2
Japan
makuwa
24
3
Yi wofeng
Shaanxi, China
makuwa
24
4
Dajing reticulatus
Japan
reticulatus
24
5
Japan
reticulatus
24
6
Baidi
Japan
inororus
24
7
Bailangua
Lanzhou, China
inodorus
24
8
81-49
Hebei, China
reticulatus
24
9
Spain
Spain
cantalupensis
24
10
Mapao melon
Shaanxi. China
wild melon
24
11
KH-242
South Asia
reticulatus
24
12
Lan pang
U.S.A.
inodorus
24
13
Dudaim

Shanghai, China

dudaim
24
14
America reticulatus
Changchun. China
reticulatus
24
15
Haidongqin
Hunan, China
makuwa
24
16
Balixiang
Heilongjiang, China
makuwa
24
17
Huanan 108
Hunan, China
makuwa
24
18
Huangli
Hebei,.. China
makuwa
24
19
Longtian-1
Heilongjiang, China
makuwa
24
20
Yilianghu
Japan
reticulatus
24
21
84-29
Hebei, China
cantalupensis
24
22
81-48
Hebei, China
cantalupensis
24
23
Huangzuixian
Xinjiang, China
cantalupensis
24
24
Baicaigua
Hebei, China
conomon
24
25
Snaky melon
Middle East
flexuosus
24
26
Lantiangua
Lanzhou, China
makuwa
24
27
Wild Hami
Xinjhiang, China
Pubescens
24
28
Lantian-5
Lanzhou, China
F1
24
29
Gold melon
Shanghai, China
makuwa
24
30
Hetian
Xinjiang, China
ssp. melo Pang.
24
31
Kaer
Xinjiang, China
ssp. melo Pang.
24
32
Baipicui
Xinjiang, China
ssp.melo Pang.
24
33
Egypt melon
Egypt
reticulatus
24, 48
34
Halesbest
U.S.A.
cantalupensis
24, 48
35
Aheqi
Xinjiang, China
cantalupensis
24, 48
36
Tetraploid
Artificial
cantalupensis
48

Table 2. Karyotype date of American muskmelon (Cucumis melo var. reticulatus) and Hetian.

Order number of Chromosome
Absolute length ( μ m)
Relative length (%)
Arm ratio (long/short)
Type
American muskmelon
1
0.93 + 0.72 = 1.65 5.65 + 4.37 = 10.02
1.29
m
2
0.86 + 0.73 = 1.59 5.22 + 4.44 = 9.66
1.18
m
3
1.09 + 0.5 = 1.59 6.59 + 3.04 = 9.63
2.17
sm
4
0.78 + 0.72 = 1.50 4.47 + 4.37 = 9.11
1.08
m
5
0.77 + 0.71 = 1.48 4.68 + 4.31 = 8.99
1.09
m
6
0.86 + 0.47 = 1.33 5.22 + 2.83 = 8.05
1.84
sm
7
0.76 + 0.54 = 1.30 4.60 + 3.28 + 7.88
1.4
m
8
0.75 + 0.54 = 1.29 4.53 + 3.28 = 7.81
1.38
m
9
0.73 + 0.53 = 1.26 4.59 + 3.13 = 7.72
1.47
m
10
0.77 + 0.49 + 1.26 4.53 + 3.03 = 7.56
1.50
m
11
0.75 + 0.49 = 1.24 4.53 + 2.98 = 7.51
1.52
m
12
0.61 + 0.54 = 1.18 3.85 + 3.28 = 7.13
1.17
m
Hetian
1
0.91 + 0.64 = 1.55 6.56 + 4.61 = 11.17
1.43
m
2
0.84 + 0.47 = 1.31 6.05 + 3.39 = 9.44
1.78
sm
3
1.78 = 0.49 = 1.27 5.62 + 3.53 = 9.15
1.59
m
4
0.75 + 0.48 = 1.23 5.4 + 3.45 + 8.85
1.57
m
5
0.73 + 0.47 = 1.20 5.26 + 4.39 = 8.65
1.55
m
6
0.69 + 0.47 = 1.16 4.97 + 2.39 = 8.36
1.47
m
7
0.71 + 0.45 = 1.16 5.12 + 3.24 + 8.36
1.58
m
8
0.66 + 0.45 = 1.11 4.76 + 3.24 = 8.00
1.47
m
9
0.55 + 0.51 = 1.02 3.67 + 3.67 = 7.34
1.0
M
10
0.49 + 0.49 = 0.98 3.53 + 3.53 = 7.06
1.0
M
11
0.51 + 0.47 = 0.98 3.67 + 3.39 = 7.06
1.08
m
12
0.49 + 0.42 = 0.91 3.53 + 3.03 + 6.56
1.17
m

Literature Cited

  1. Li, Moxue. 1985. Wuhan Plant Study. 3(14):297-303.
  2. Li, Rongquian. 1989. Study on Chinese vegetable plant karyotype. Wuhan University Print Agency.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 11 December, 2009