Variation for Interspecific Crossability of Cucumis anguria L. and C. zeyheri Sond.

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Cucurbit Genetics Cooperative Report 6:100-101 (article 51) 1983

D. L. Visser and A. P. M. den Nijs
Institute for Horticultural Plant Breeding, P. O. Box 16, Wageningen, The Netherlands

Cucumis anguria L. and C. zeyheri Sond. are both resistant to cucumber green mottle mosaic virus, a serious disease of glasshouse cucumbers. The resistance of C. anguria is due to a single dominant gene, Cgm (3), but the inheritance in C. zeyheri is as yet uncertain. Crosses between both species were made to find out if the resistances are genetically identical.

Although pollen tubes of C. zeyheri 2x penetrate into the ovules of C. anguria (2) and fruits set, no viable seeds were obtained (1, 2). The reciprocal cross (C. zeyheri 2x x C. anguria) yielded viable seeds, and F1 plants were reported by Dane, et al (1). We also obtained viable seeds, but the F1 plants died (4). Differences in occurrence of seedling death appeared to depend on the combination of accessions of both species. Therefore, more crosses were made involving 8 accessions of C. anguria (4 of which belong to var. longipes A. Meeuse), and 6 accessions of C. zeyheri (5 diploid, and one tetraploid). The latter species has erroneously been referred to as C. africanus L.f. in earlier reports (5). Five plants per accessions were cultivated and pollinated in an insect-proof glasshouse in the summer of 1981. Progenies were screened for occurrence of seedling death in 1982.

C. anguria and C. anguria var. longipes gave different results in the crosses with C. zeyheri 2x. In the combination C. anguria x C. zeyheri 2x, none out of 216 seeds from 6 fruits (10% fruit set) germinated. Fruit set was generally high in the reciprocal cross and many seeds were obtained, but seedling death. of the F1 plants prevailed. One exceptional accession of C. zeyheri, however, yielded in combination with 3 out of 4 accessions of C. anguria a small number of weak seedlings which developed into fairly fertile hybrids (Table 1).

Table 1. Percentage of fruit set following pollinations of C. zeyheri by C. anguria and C. anguria var. longipes, and occurrence of seedling death in the F1 (5 pollinations per cross).

Ploidy of

Female

Parent

(C. zeyheri)

Male Parent

C. anguria

C. anguria var. longipes

Gbn 0307 0310 1970 2067 0198 1784 1736 1827
2x 0162 100 D  80 D  60 D 60 D  80 D  20 D 100 +  20 +
0181  80 D 100 D 100 D 60 D 100 D  60 D  60 +  20 +
0330  80 D  40 D 0 0  60 D  20 D 100 D  40 +
2065 100 D  60 D 100 + 60 100 D 100 D  60 +  60 +
1787  20 +  30 +  70 S  60 + 0 0 0 0
4x 1457  20 + 100 +  80 + 100 +  80 +  40 + 100 + 100 +
S = no germination; D = seedling death of F1 plants; + = normal F1 plants.
Note: Gbn (Gene bank no.) 0307 = PI 196477; 0310 = PI 233646; 1787 = PI 299569; 1457 = PI 299570.

The crosses of C. anguria var. longipes x C. zeyheri 2x yielded 7 fruits with 182 seeds out of 135 pollinations. Seed of only one combination of accessions germinated and gave rise to weak, sparingly fertile hybrids. The reciprocal combinations were more successful; 2 of the 4 accessions of C. anguria var. longipes produced many vigorous and fertile hybrids with all but one of the accessions of C. zeyheri 2x. All hybrids made with the other two accessions exhibited seedling death. The behavior of C. zeyheri Gbn. 1787 in this combination is also remarkably different. It distinguishes C. anguria from C. anguria var. longipes (Table 1).

All diploid haploids were characterized by fully intermediate fruit shape. Fruits of both reciprocal crosses of C. anguria var. longipes and C. zeyheri, were indistinguishable.

The cross C. zeyheri 4x x C. anguria and C. anguria var. longipes yielded many vigorous, but sterile, F1 plants. The reciprocal cross, with the tetraploid species as pollen parent, gave 2 fruits out of 25 pollinations, and several sterile hybrids were raised.

We conclude that there is sufficient variation within C. anguria (notably in var. longipes) and within C. zeyheri 2x to overcome the crossability barrier between the two species. Analysis of the inheritance of the virus-resistance is in progress.

Literature Cited

  1. Dane, F., D.W. Denna and T. Tsuchiya. 1980. Evolutionary studies of wild species in the genus Cucumis. Z. Pflanzenzucht. 85:89–109.
  2. 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.
  3. Nijs, A. P. M. den. 1982. Inheritance of resistance to cucumber green mottle mosaic virus (Cgm) in Cucumis anguria L. Cucurbit Genetics Coop. Rpt. 5:57–58.
  4. Nijs, A.P.M. den, D.L. Visser and J.B.M. Custers. 1981. Seedling death in interspecific crosses with Cucumis africanus L.f. Cucurbit Genetics Coop. Rpt. 4:58–60.
  5. Varekamp, H.Q., D.L. Visser and A.P.M. den nijs. 1982. Rectification of the names of certain accession of the IVT – Cucumis collection. Cucurbit Genetics Coop. Rpt. 5:59–60.