Interspecific hybrids between Cucumis hystrix Chakr. (2n = 2 x = 24) and Cucumis sativus L. (2n = 2 x = 14) were produced by means of F(1) (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 BC(1)S(1) 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.

A synthetic amphidiploid species Cucumis hyriviis Chen & Kirkbride (2n -4x -38; genome designated as HHCC) has recently been created from an interspecific mating between C. saiivtis L. (2n -2x = 14: genome designated as CC) and C. hyslri.\ Chakr. (2n -2x -24; genome designated as HH). This amphidiploid is resistant to root knot nematode. tolerant io low irradiance. and has higher nutritional value than standard processing cucumber cultivars. An allotriploid (2n 3 x -26; HCC) was derived frotii a cross between C. stiiivu.s L. and C. hvfivus Chen & Kirkbride. Diploid meiotic behaviour in C. saliviis and C. hysni.x involves the development of seven and 12 metaphase bivalents respectively. In the derived allotriploid. univalents. bivalents, and trivalents (at relatively low frequency) were observed at metaphase I indicating that some homeologues from the C and H genomes can synapse. Based on a comparative karyotype analysis of cucumber (i.e. chromosome size and pairing behaviour) and aliotriploid plants, ihe seven bivalents observed at metaphase I were ascertained to be cucumber homologtics. while the !2 univalents were of C. hystrix origin thus confirming the allotriploid karyotypic constitution to be HCC. On average, the frequency of trivalent.s was 0.24 at diakinesis and 0.22 in 100 meiocyles at metaphase I. indicating the possibility of genetic exchange due to the homoeology between the C and H genomes. After simultaneous cytokinesis, only polyads were observed in pollen mother cells (PMCs) at telophase II, which led to the production of sterile pollen grains. Multi-polarization of chrotnosomes was dominant at anaphase II. However, in about 20% PMCs. chromosotnes separated to form a 7C + I 2H complement, suggesting a possible method for the production of alien addition cucumbcr-C hvstrix hnes through fnrther backcrossing of the allotriploid to diploid cucumber.