Evaluation of Five Commercial Cucumber Hybrids for Downy Mildew Disease Using RAPD, SCoT and SRAP Molecular Markers

Downy mildew (DM) is the most devastating leaf disease of cucumber (Cucumis sativus L.) caused by the Oomycete Pseudoperonospora cubensis. The resistance mechanism of DM is still poorly understood in cucumber plants. In the present investigation, one moderately tolerant (Elnems), two susceptible (Barika F1and Basimah F1) and two tolerant (234 and SV4196CD) cucumber hybrids to DM were used. Genetic diversity was assessed using three types of molecular markers RAPD, SCoT and SRAP. In addition, selected candidate PCR bands were sequenced to investigate the possibility of identifying anonymous genes in cucumber hybrids related to DM tolerance. The results showed that the total number of bands produced by RAPD, SCoT and SRAP were187, 237 and 208, respectively. The polymorphism percentage revealed by RAPD, SCoT and SRAP was 80.75%, 75.95% and 86.54%, respectively. The resulting dendrograms successfully clustered the two tolerant hybrids 234 and SV4196CD in the same cluster. These two hybrids appear to be genetically related, although the sources of the hybrids are different. Elnems, Barika F1 and Basimah F1were also clustered together. The polymorphic fragments present only in the tolerant hybrids have been isolated, sequenced and aligned with the nucleotide sequences in the database. The alignment sequences revealed that one amplicon (M1E7D1-ME1) showed homology with Photosystem I P700 chlorophyll a apoprotein A1 (PsaA) protein, which could be related to DM tolerance. More studies are required to clarify the mechanism of DM resistance in cucumber.