Comparison of crown and root inoculation method for evaluating the reaction of sugar beet cultivars to Rhizoctonia solani AG 2-2 IIIB

Sugar beet (Beta vulgaris L.) is the second major economically important sugar-yielding crops in the world and the US ranked third in world sugar beet production. Sugar beet crown rot and root rot are caused by Rhizoctonia solani (Khün) is a serious threat for sugar beet production and processing. Prior to the adoption of Roundup Ready® sugar beet (RRSB) cultivars, crown rot was a serious problem caused by mechanical tillage operations required for weed control. Following the introduction and large-scale cultivation of RRSB, however, crown rot was reduced but root rot became severe. This necessitated reassessment of screening methods for development of Rhizoctonia resistant cultivars. In this study we evaluated two inoculation methods, viz. crown inoculation and root inoculation methods for development of Rhizoctonia root rot and assessed their efficacy to differentiate the reaction of sugar beet cultivars. The results of this study demonstrated that the root inoculation method is optimal for consistent disease rating of the germplasms in the greenhouse. It was concluded that use of root inoculation method is convenient and accurate for screening of RRSB cultivars in a resistance breeding program.