Reproduction and cytogenetic characterization of interspecific hybrids derived from Cucumis hystrix Chakr. x Cucumis sativus L.

Interspecific hybrids between Cucumis hystrix Chakr. (2n = 2x = 24) and Cucumis sativus L. (2n = 2x = 14) were produced by means of F, (2n = 19) embryo rescue and subsequent chromosome doubling. The hybridity was confirmed by genomic in situ hybridization (GISH) and chromosome analysis. The amphidiploid (2n = 38) was self-pollinated and backcrossed to cucumber resulting in lines with improved crossability to C. sativus. Examination of shape, stainability, and germination rate of pollen grains and yield as a function of mature fruit set per ten pollinated flowers indicated a tendency for increased fertility in BC1S1 progeny when compared to F-1 and amphidiploid offspring. Cytogenetic characterization of F-1 and amphidiploid progeny was performed. Generally normal meioses produced viable pollen grains, and fertilization resulted in partial fertility restoration in amphidiploid progeny. Chromosome anomalies such as "frying-pan trivalent", chromosome lagging and spindle mis-orientation were also observed. In most of the PMCs of the F-1 diploid hybrid progeny, 19 univalents were observed at diakinesis and MI. In the amphidiploid, more than 90% of the configurations at MI consisted of the predicted 19 bivalents and less than 5% contained multivalents [trivalents (2.3%) + quadrivalents (0.3%)], suggesting the presence of preferential pairing, and a distinctive parental genome, as well. The chiasmata observed between homoeologous chromosomes further demonstrated the introgression of the C. hystrix genome into that of C. sativus.