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Cucurbit Genetics Cooperative Report 14:69-70 (article 26) 1991

Interspecific Hybridization in Cucumis spp.

M. Chatterjee and T.A. More

Division of Vegetable Crops, Indian Agricultural Research Institute, New Delhi, India 110012

Research work conducted in this Institute revealed that high level resistance to cucumber green mottle mosaic virus (CGMMV) is not available in cultivated forms of melon (Cucumis melo L.). Nevertheless, five wild Cucumis species vis, C. figarei, C. zeyheri, C. meeusii, C. myriocarpus and C. africanus were identified as immune to CCMMV. (4, 5). Besides, in the first four species a complete resistance to Fusarium wilt caused by Fusarium oxysporum sp.melonis was confirmed from the field as well as artificial inoculation screenings (Thomas and More, 1990). Hence, attempts were made to cross these wild Cucumis species with cultivated forms of C. melo.

Sixteen interspecific crosses were made by crossing four wild species with two cultivated forms of melon (Pusa Madhuras and Monoecious-4) and their eight reciprocal crosses were attempted under field conditions by conventional hybridization procedure. Fruit set was not obtained in any of the crosses (Table 1) nor was it obtained in their reciprocal crosses. This indicated the presence of strong barrier to interspecific hybridization of Cucumis.

In order to determine the exact nature of barrier, all the 16 crosses were subjected to fluorescence microscopic study, based on method described by Kho and Baer (1968) and modified by Tomer and Gottreich (1975). Cross-pollinated stigmas were collected 24, 48, and 72 h after pollination and immediately fixed in 3:1 AA (absolute alcohol 3, acetic acid 1). After 24 h in fixative the stigmas were washed in water and sectioned free hand longitudinally. Each section was softened in 8N NaOH for 1 h, washed with water and stained with 0.005 oper cent aniline blue dissolved in 0.05 M Na2HP04 (Sodium-bi-phosphate, pH 8.2 containing 20% glycerol). The stained tissues were then placed on a slide in glycerine and gently squashed by applying pressure on the cover slip. Observations were made on Nikon microphot equipped with a 200W high pressure mercury lamp illuminated at 380-490 nm by use of transmission filter BA 530 in the oculars. Selfed stigmas in each case were also observed as control. In crosses, C. figarei x C. melo (M$), C. meeusii x C. melo (M4), and C. zeyheri x C. melo (M4) and their reciprocals the pollen grains were bound on the stigma without any change even 72 h after pollination. Not a single pollen grain germinated in any of these crosses. As expected, inthe selfings of C. figarei, C. meeusii and C. zeyheri severalpollen grains had germinated and pollen tubes reached to the ovule.

Inability of pollen of C. melo to germinate on the stigmas of C. figarei, C. meeusii and C. zeyheri and the pollen of these species on C. melo stigmas, even up to 72 h after pollination, indicated that a pre-fertilization barrier is involved in the failure of interspecific hybridization in Cucumis. Interestingly, the present results provided evidence for the existence of a strong barrier at very first stage of interspecific hybridization (i.e., non-pollen germination). Similar observations were made for C. metuliferus, C. ficifolius, C. prophetarum, C. zeyheri and C. myriocarpus interspecific crosses with C. melo (1). In most of the earlier reports on this aspect, the pollen germinated and the failure occured after the post-pollen germination stage. Only in C. melo x C. metuliferus cross was there evidence of a post-fertilization abortion (3). Based on these results, some advanced biotechnological tools such as somatic hybridization might be useful in solving the problem of interspecific hybridization in Cucumis.

Table 1. Fruit set in interspecific crosses.

Cross
No. of flowers pollinated
No. of fruits obtained
1. C. figarei x C. melo (PM)
50
0
2. C. melo (PM) x C. figarei
100
0
3. C. zeyheri x C. melo (PM)
50
0
4. C. melo (PM) x C. zeyheri
100
0
5. C. myriocarpus x C. melo (PM)
50
0
6.C. melo (PM) x C. meeusii
100
0
7. C. meeusii x C. melo (PM)
50
0
8. C. melo (PM) x C. meeusii
100
0
9. C. figarei x C. melo (M4)
50
0
10. C. melo (M4) x C. figarei
100
0
11. C. zeyheri x C. melo (M4)
50
0
12. C. melo (M4) x C. zeyheri
100
0
13. C. myriocarpus c C. melo (M4)
50
0
14. C. melo (M4) x C. myriocarpus
100
0
15. C. meeusii x C. melo (M4)
50
0
16. C. melo (M4) x C. meusii
100
0
Total
1200
0

Literature Cited

  1. Dumas De Vaulx, R. 1979. Pollen Germination in interspecific crosses between muskmelon and some wild Cucumis species. Cucurbit Genetics Cooperative 2:20-23.
  2. Kho Y.O. and J. Baer. 1968. Observing pollen tubes by means of fluoescence. Euphytica 17:298-302.
  3. Norton, J.D. and D.M. Granberry. 1980. Characteristics of progeny from interspecific cross of Cucumis melo L. with C. metuliferus E. Mey. J. Amer. Soc. Hort. Sci. 105:174-180.
  4. Rajamony, L., T.A. More, V.S. Seshadri, and A. Varma. 1987. Resistance to cucumber green mottle mosaic virus (CGMMV). Phytopathologische Z. 129:237-244.
  5. Rajamony, L., T.A. More, V.S. Seshadri, and A. Varma. 1990. Reaction of muskmelon collections to cucumber green mottle mosaic virus (CGMV). Phytopathologische Z. 129:237-244.
  6. Thomas, P. and T.A. More. 1990. Screening wild Cucumis spp. in the field and with artificial seed inoculation against Fusarium oxysporum sp. melonis. Cucurbit Genetics Cooperative 13:18-19.
  7. Tomer, E. and M. Gottreich. 1975. Observations on the fertilization process in avocado with fluorescent olight. Euphytica 24:531-535.
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