Abstract: Cultivated cucumber‘Beijing Jietou’ (Cucumis sativus L. , 2n = 14) was backcrossed to the synthetic amphidiploid species C. hytivus (2n = 38) , and the progenies were selfed. All the plants were tested for downy mildew resistance by field inoculation. One plant HH12825 possessing resistance was identified in the BC₁ F₂ population. The HH12825 was compared with the cucumber and the wild Cucum is species C. hystrix in morphology and cytology. The result indicated that some of its morphological characters were intermediate between the two parents, e.g. , leaf area, internodeps length, and fruit length ×diameter, while some of them were closer to the wild species, e.g. , number of lateral branches, fruit spines color. In cytology, observations from meiotic process indicated much higher frequencies of multivalents (56% ±8%) atmetaphase I and chromosome lagging rate (72% ±5%) at anaphaseⅠ in the pollen mother cell ( PMC) , indicating typical behavior of a translocation plant. Random amplified polymorphic DNA (RAPD) analysis was carried out with the genomic DNAs of HH12825. Two p rimers E219: ACGGCGTATG and A I220: CCTGTTCCCT from 40 random primers selected could amplify a special repeatable DNA sequence from C. hystrix in the plant and thus its translocation nature was confirmed, and its was named as CT201, thereafter.

Key words: Cucumber, Alien translocation line, Downy mildew, Cytology, RAPD marker