Screening For Downy Mildew Resistance In Cucumber Introgression Lines

Downy mildew is caused by Pseudoperonospora cubensis(Berk.& Curt.) Rostov, and is a major foliar disease of cucumber in the world.Owning to narrow genetic base and lack of resistant resource,downy mildew resistance is still a problem to be solved in cucumber breeding program.In this dissertation,amphidiploid species Cucumis hytivus containing whole sour cucumber genome,in which there is resistant gene to downy mildew,was backcrossed to cultivated cucumber and its progenies were selfed. And we got the cucumber introgression lines.The continuous test of resistance to downy mildew,combining with morphology, physiology,biochemistry and molecular marker done to above progenies,cucumber introgression line with resistance to downy mildew were screened.1 Screening for Downy Mildew Resistance in Cucumber Introgression LinesTwenty cucumber introgression lines from interspecific hybridization between cultivated cucumber and wild Cucumis species C.hystrix were evaluated for downy mildew resistance,using methods of greenhouse inoculation at seedling stage and open field observation at grown up stage.Six introgression lines were found with resistance,which is meaningful to cucumber downy mildew resistance breeding. Ratings from the two experiments are highly correlated,suggesting that cucumber downy mildew resistance can be tested through inoculation at seedling state.2 Changes of POD isoenzyme pattens before and after introgression lines of cucumber get downy mildewUsing common resistance and susceptible cucumber cultivar as controls,POD isoenzyme pattens of cucumbers of 19 accessions derived from wide cross between cucumber and sour cucumber were tested for downy mildew resistance.Result of POD isoenzyme pattens of cucumbers after inoculation were different indicated that the inheritance of introgressive lines to downy mildew disease and expression of peroxidase diversify.3 Relationship between activity changes of relative electrolyte conductivity and resistance to cucumber downy mildewTo understand the relationship between activity changes of relative electrolyte conductivity and resistance to cucumber downy mildew we utilized the cucumber downy mildew(CDM)-resistant line US627,jinchun4,and susceptible line xintaimici, and analyzed relative electrolyte conductivity of cucumbers in the greenhouse at seedling time and field at mature time.The correlation between relative electrolyte conductivity and greenhouse seedling rating test have been studied which was correlated.And we found that relative electrolyte conductivity activity of resistant cucumbers were under 0.350 after inoculation at seedling time.Therefore,the presented relative electrolyte conductivity methodology can be used as indicator in screening resistance cucumber to downy mildew.4 Investigation on the morphological diversity of Cucumber introgression lines22 morphological characters were investigated in 22 Cucumber introgression lines.The results showed that the morphological diversity was high among cucumber introgression lines.The average diversity index was 0.52.The morphological diversity of qualitative traits was overall higher than that of quantitative traits.The average variant coefficient was 32.7%。...