Evaluation of Five Cucumber Hybrids for Downy Mildew Disease Using RAPD, Scot and SRAP Markers

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Fatma A. Elshazli, Basita A. Hussein, Ahmed K. Hatem, Mohamed H. Soliman, Neama. H. Osman


Downy mildew is a major disease of cucumber (Cucumis sativus L.) caused by the Oomycete Pseudoperonospora, this disease leads to heavy economic and yield losses. In the present study, the genetic variability and relationships among the five cucumber hybrids two tolerant (234 and SV4196CD), one moderate tolerant (Elnems) and two susceptible to downy mildew (Barika F1 and Basimah F1) were assayed using 14 RAPD,13 SCoT and 16 SRAP combinations to identify the polymorphic markers related to the downy mildew tolerance using the bioinformatics tools. The data showed that the total number of amplicons produced by the RAPD, SCoT, and SRAP was 187, 
237, and 208, respectively. The level of polymorphism among the five genotypes revealed by RAPD, SCoT, and SRAP was 80.75%, 75.95%, and 86.54%, respectively. All dendrograms showed similar separating, and it is interesting to note that the two genotypes 234 and SV4196CD (tolerant to DM) were clustered together as in the independent RAPD, SCoT, SRAP and combined data. Moreover, these two genotypes appear to be genetically related as they formed one group in all dendrograms based on RAPD, SCoT, SRAP and combined data. While, the susceptible and moderate tolerant genotypes were placed in the other cluster. From the sequencing analysis of the polymorphic fragments that present only in the tolerant hybrids, one amplicon (M1E7D1-ME1500) showed homology with Photosystem I P700 chlorophyll an apoprotein A1 protein (PsaA) which could be related to the downy mildew tolerance.  Clearly, more studies are required to provide sufficient data elucidating the mechanism of downy mildew resistance in the cucumber.

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