Abstract
Downy mildew is one of the major foliar diseases of cucumber in which the new resistant cucumber cultivars are necessary to control this disease. Before improving the new cultivar, knowing the information about genetic diversity of cucumber germplasm is necessary. Thus, the objective of this study is to evaluate the genetic diversity of downy mildew resistant/susceptible cucumber germplasm. Forty cucumber accessions were screened for downy mildew disease reaction and were classified into five classes which the average of percent of symptomatic leaf area ranged from 20.1% (highly resistant) to 95.0% (highly susceptible). Then, these cucumber germplasms were analyzed with 20 inter simple sequence repeat (ISSR) markers. A total of 17 ISSR primers (85%) could amplify in all 40 cucumber accessions with the percent of polymorphic bands of each primer ranged from 55.56% to 100%. The polymorphism information content (PIC) ranged from 0.12 to 0.45 with the mean of 0.25, while the resolving power (RP) averaged at 1.82 and ranged from 0.50 to 3.20. The phylogenetic tree and principal component analysis revealed the association between downy mildew disease reaction and country of the origin of cucumber germplasm which could help the cucumber breeders to select the parental lines for improving the new cultivars that resist to downy mildew in the future.
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