Evaluation of superior sugar beet genotypes for resistance to important root rot pathogens in the greenhouse

Four sugar beet genotypes with different reactions to root rot pathogens were evaluated for resistance to important root rot agents including Pythium aphanidermatum, Phytophthora drechsleri, Rhizoctonia solani AG-2-2 and R. solani AG-4. Inoculums for Pythium and Phytophthora were 3-5 day actively growing colony of the pathogens on CMA medium, while for Rhizoctonia isolates were nine infected corn kernels. Evaluation of resistance to the pathogens was carried out in separate experiments as completely randomized design with three replications. Diseases severity index was measured a month after inoculation based on the available scales. The results showed that genotypes SB19-P.16, SB19-P.44 and SB19-P.78 were rather tolerant to Pythium rot. The genotype SB19-P.78 showed the lowest infection symptoms to Phytophthora rot after the resistant cultivar (Dorotea). Evaluation of sugar beet genotypes for Rhizoctonia root rot resistance showed that the genotype SB19-P.16 had a lower infection rate to AG-4 which was very close to Dorotea. Genotypes SB19-P.78, SB19-P.16 and SB19-P.44 were not significanly different from Dorotea with regard to resistance to R. solani AG-2-2. It seems that SB19-P.16, SB19-P.78 and SB19-P.44 genotypes could be included in the breeding programs to increase the resistance of sugar beet varieties. It is recommended to further evaluate these genotypes in additional experiments. In this paper, we are reporting resistant genetic germplasm of sugar beet to P. aphanidermatum and P. drechsleri for the first time in Iran.