Cyto-Molecular Tracking of Alien Chromosome Components During the Process of Introgressive Breeding of Cucumber

Cucumis × hytivus Chen & Kirkbride is a synthesized allotetraploid between cultivated cucumber (C. sativus L., 2n = 2x = 14) and its wild relative ‘sour cucumber’ (C. hystrix Chakr., 2n = 2x = 24). This novel interspecific hybrid in Cucumis can be used as a bridge to transfer the chromosome component from the wild species to cucumber through sequential backcross. We used SSR markers and genomic fluorescence in situ hybridization (GISH) to track the alien chromosome components during the process of the introgressive breeding. We obtained an allotriploid derived from backcrossing C. × hytivus to C. sativus L. The GISH results showed clearly that the allotriploid has 26 chromosomes including 14 chromosomes of cucumber and 12 of C. hystrix. Furtherly, sequential backcrosses up to six generations using C. sativus as recurrent parent, followed by three generations’ selfing were carried out to create an introgression population with a genetic background of cultivated cucumber. Combining molecular marker and GISH techniques, an introgression population with 50 individuals were constructed. The sizes and locations of alien chromosome components along the cucumber genetic background were characterized. Totally 149 chromosomes introgression fragments were detected in those lines. The length of introgression fragments is between 1.65~15.4 cM with the average 5.41 cM distributing in 7 chromosomes of cucumber. The total length of the different alien fragments is 259.95 cM and the coverage of the cucumber genome is 45.37%.