Cucurbit Genetics Cooperative Report 5:57-58 (article 27) 1982
A.P.M. den Nijs
Institute for Horticultural Plant Breeding, P.O. Box 16, Wageningen, The Netherlands
Cucumber green mottle mosaic virus (Cgm), first described by Ainsworth (1), causes significant losses in the glasshouse culture of cucumbers in Western Europe and Japan (3, 5). Strict phytosanitary measures are necessary to minimize the damage. Symptomless carriers have been found among cucumber varieties of Asiatic origin, but the reduction in yield after inoculation was similar to that in susceptible varieties (5). No resistance has been observed within C. sativus L., but several wild Cucumis species of African origin proved to be resistant (6). One of these, C. anguria L. has also some resistance to root knot nematodes and bean spider mites (6).
Attempts to cross C. anguria, the West Indian Gherkin, with either cucumber or melon have thus far failed (2, 4, 6). Nevertheless, there appears to be a possibility that some kind of hybridization, be it conventional or novel, can be achieved between C. sativus and C. anguria. Therefore, it seemed appropriate to reveal the genetics of the resistance to Cgm in the later species.
Since no susceptible segregants were identified in any of the 14 accessions of C. anguria in our collection, outcrosses to the related susceptible species C. myriocarpus Naud. were made to produce segregating progenies for genetic analysis. The crosses and analysis of resulting progenies are in Table 1. The initial cross was only successful when anguria was the female present, whereas in the reciprocal, pollen tubes are arrested in the upper part of the style (4). The resulting hybrids were vigorous and reasonable self-fertile. Crosses with subspecies longipes of C. anguria as maternal parent were more difficult, and the F1plants sparingly self-fertile, so for this analysis only C. anguria ssp. anguria was used. All seedlings were tested by rubbing the cotyledons with a suspension of the virus with carborundum, which has proved a fully effective technique for infection. Since symptoms of the virus infection are sometimes hard to distinguish in C. myriocarpus, sap of all symptomless individuals was applied to tested plants of a cucumber line with clear symptoms for ultimate classification.
The segregations listed in Table 1 are combined data of different families which behaved in similar fashion. Despite the fact that distorted gene segregations could be expected because of the interspecific nature of the cross, the data clearly fit a monogenic inheritance pattern. Therefore, I conclude that one dominant gene confers resistance to Cgm in C. anguria. Following the guidelines adopted by the CGC, I propose to designate this gene Cucumber green mottle mosaic virus resistance, symbol Cgm.
This is to my knowledge the first validly described gene in C. anguria. Earlier Meeuse (7) referred to the dominant gene for bitterness in subspecies longipes, in part on unpublished segregation data by Rehm. A similar genetical analysis, as presented above, was also attempted with Cgm resistant C. zeyheri Sond. (2x), but, until now, segregations have been inconclusive. It is also yet to be established whether the resistances in both species are identical or not.
Table 1. Distribution of plants and chi-square analysis of resistance in Cgm in crosses between C. anguria and C. myriocarpus.
Number of plants |
|||||
Type of cross |
Number of families |
Susceptible |
Resistant |
Tested ratio |
p-value |
| (a x m) | 4 | 0 | 42 | 0 : 1 | – |
| (a x m) self | 3 | 11 | 37 | 0 : 3 | 0.75 |
| [(a x m)] self m | 1 | 1 | 40 | 0 : 1 | – |
| [(a x m)] self a | 1 | 0 | 9 | 0 : 1 | – |
| (a x m) self self | 1 | 2 | 11 | 1 : 3 | 0.42 |
| (a x m ) m | 2 | 44 | 47 | 1 : 1 | 0.73 |
| [(a x m) m] self | 2 | 2 | 9 | 1 : 3 | 0.53 |
| [(a x m) m] m | 2 | 24 | 24 | 1 : 1 | 1.00 |
| (a x m) a | 5 | 0 | 56 | 0 : 1 | – |
Literature Cited
- Ainsworth, G.C. 1935. Mosaic diseases of the cucumber. Ann. Appl. Biol. 22:55-67.
- Deakin, J.R., G.W. Bohn and T.W. Whitaker. 1971. Interspecific hybridization in Cucumis. Econ. Bot. 25:195-212.
- Hollings, M., Y. Komuro and H. Tochihara. 1975. Cucumber green mottle mosaic virus. C.M.J./A/A.B. Descriptions of Plant Viruses, October, no. 154.
- Kho, Y.O., A.P.M. den Nijs and J. Franken. 1980. Interspecific hybridization in Cucumis (L). II. The crossability of species, an investigation of in vivo pollen tube growth and seed set. Euphytica 29:661-672.
- Kooistra, E. 1968. Significance of the non-appearance of visible disease symptoms in cucumber (Cucumis sativus L.) after infection with Cucumis virus 2. Euphytica 17:356-140.
- Kroon, G.H., J.B.M. Custers, Y.O. Kho, A.P.M. den Nijs and H.Q. Varekamp. 1979. Interspecific hybridization in Cucumis (L.) I. Need for genetic variation, biosystematic relations and possibilities to overcome crossability barriers. Euphytica 28:723-728.
- Meeuse, A.D.J. 1958. The possible origin of Cucumis anguria L. Blumea Suppl. IV:196-205.