Studies On Cyto-and Molecular Genetics In Cucumis Interspecific Hybrid (C.hytivus Chen And Kirkbride) And The Phylogenetic Relationships In Cucumis Species

1 Studies of cytological and molecular genetics on the amphidiploid species C. hytivus and its progeniesThe behavior of chromosome at diakinesis and Metaphase I in meiosis was observed in C. hytivus. About 46.3% of pollen mother cells (PMCs) had the univalent or multivalent and the average chromosome configuration was 0.56I + 17.36II + 0.35III + 0.26IV + 0.046V + 0.056VI. In PMCs of the progeny of the allotriploid backcrossed C. hytivus with cucumber, heterobivalent formed within the C. hystrix chromosomes and trivalent formed with two cucumber chromosomes and one C. hystrix chromosome, but the frequency was low. The average chromosome configuration of C. hystrix was 11.53I + 7.16II + 0.05III at meiotic.RAPD and SSR markers were used to investigate the DNA fingerprints of C. hytivus. Six specific RAPD bands (A-15/2000bp, 480bp, G-02/1750bp, AP-03/700bp, AP-07/640bp, and AP-07/700bp) and four specific SSR sites (CMCT160a+b/380bp, CSCTTT15a/280bp, CMCC- A145/190bp, and CMGA165/190bp) were found. The specificity of 3 SCAR markers converted from the specific RAPD markers of C. hytivus were analyzed. SAP-03/700 primer pair was specific to C. hytivus, while it produced one different band in cucumber cultigens and C. sativus var. hardwickii, respecitively. SAP-07/640 primer pairs yielded the same band in C. hystrix and C. hytivus and it was not specific. SAP-20/700 was false positive marker and yielded no band in the 16 accessions. Compared with the sequence of 3 different bands yielded by SAP-03/700 primer pair in C. hytivus, C. sativus var. sativus and C. sativus var. hardwickii, ~ 200 bp sequence at the ends of the bands were similar while the middle parts were different. In addition, about 200 bp of SAP-03/700 was homologous with cucumber mitochrodial genome, but the directions were contrary.The fruit set percentage and number of seeds produced in the crosses between amphidiploid C. hytivus, allotriploid, and different ecotype cucumber cultigens were high (83-100%). The ratio of fruit with embryo was 60-67% in the cross between amphidiploid C. hytivus and cucumber cultigens. Each fruit had about 10-20 embryos, all of which could survive and develop into whole plants through embryo rescue. The chromosome number of these plantlets was 26. When cucumber cultigens crossed with amphidiploid C. hytivus, only one fruit with about 180 embryos was obtained and 80% of the embryos could survive through embryo rescue, and the chromosome number of them was 26. The other two fruits produced 60 seeds (as HH1 population) and 15 (as HH2 population) with 14 chromosomes, respectively. Few fruits with embryos or seeds were obtained in reciprocal crosses between allotriploid and cucumber cultigens. One fruit had 23 seeds (as HH3 population) and theother five had one seed each. All of them had 14 chromosomes. The fruit set percentage of allotriploid selfed was lower (48-75%) and all fruit had no embryo and seed which could develop into plantlets. In HH1 population, some plants showed the origional parent C. hystrix traits such as black spines on fruit, multiple branching habits, while some had unique morphological characteristics such as orange skin of fruit. The black spines trait was tightly linkage with the orange skin trait. Nineteen SSR primer pairs produced 63 alleles in HH1 and 24 alleles (38.1%) were segregated, which was similar to the genetic diversity (37.7%) about 11 different ecotype cucumber cultgens. Eight of them might come from C. hystrix. Twenty-four arbitrary primers produced varied primed sites and among the 186 primed sites generated 31.7% were segregated. This was similar to the genetic diversity (33.0%) of the different ecotype cucumber cultgens. Both of them were significantly higher than the genetic variation (SSR: 27.1%, RAPD: 23.9%) of HHzl population produced from cross between Chinese cucumber CC3 and American pickling cucumber "A309". The results suggested that the genetic base of cucumber could be improved through interspecific hybridization and introgression.2 Studies on the response...