Control of damping-off disease caused Rhizoctonia solani Kühn on cucumber seedlings in Duhok province of Northern-Iraq

In this study, it was aimed to investigate the isolation, identification, pathogenicity, diseases incidence, disease severity and management options of cucumber seedlings damping-off caused by R. solani. During sampling, cucumber plants were collected randomly from farmers' fields in different locations at Duhok province (Shekhan, Semil, Zawita and Zakho), during 2015 and 2016 growing seasons. In-vitro pathogenicity tests of R. solani were tested on three cucumber varieties (Sayff F1, Rainbow F1 cultivar and local genotype ) by test tube method. The result revealed that there was significant effect of R. solani on three cucumber cultivars. The percentage of reduction in root length of Sayff cv. and Rainbow cv. seedlings were 38.00% and 35.82% respectively while in the local genotype it was 70.87%. In the pathogenicity tests performed under greenhouse condition, it was determined that the pathogen R. solani isolate caused damping off on susceptible Sayff F1 at pre and post emergence, and the disease severity was 50.66% and 13.46%, respectively. Research activities against R. solani were carried at under laboratory and greenhouse conditions with chemical and biological fungicides. Biological ( Biocont-T and Biohealth-WSG) and chemical (Topsin-M and Beltanol-L) fungicides were added individually and mixture to PDA at different concentrations (5 %, 10 %, and 15 %) in the laboratory studies and the growth of R. solani was measured. The application of fungicides under greenhouse condition indicated that Biohealth-WSG and Topsin-M fungicide showed lowest pre- emergence infection 20% and 30% respectively; whereas the result of post – emergence damping off showed thatboth Biocont-T 7.63% and Biohealth-WSG 8.33% considered as the most resistant bio fungicide which significantly reduce the infection compared with control treatment. The effect of different chemical and Bio-fungicides on the growth of cucumber seedlings were also tested. Maximum value in the length of root, length of vegetative growth, fresh and dry weight of root (4.70 cm, 4.20 cm, 0.79 gr and 0.14 gr respectively) were recorded in seedlings raised in pots treated with Biocont-T with significant different from control treatment