Pathogenicity, morphological and molecular characterization of Rhizoctonia spp. isolates from strawberry plants in Israel

Methyl-bromide is currently used as a soil fumigant for strawberry. However, its use is restricted internationally and in Israel from 2005. Thus, soil borne pathogens including Rhizoctonia spp., may cause more serious losses than previously reported. It is therefore important to study Rhizoctonia populations on strawberry in Israel. Anastomosis grouping (AG), the method currently used to classify Rhizoctonia isolates, is accurate and widely used; however, it is time and labour consuming. In addition, certain isolates do not self anastomose, or anastomose with more than one group. In the present work, rDNA-ITS sequence multiple alignment was used to classify the isolates. The isolates were consistently clustered according to their AGs. Currently, determination of pathogenicity of Rhizoctonia spp. isolates on strawberry is based on reduction of plant biomass rather than on specific disease symptoms. The duration of this test is relatively time-consuming (3-5 weeks). Based on inoculation of strawberry petioles, fruit and young seedlings derived from strawberry seeds, inoculation of seedlings at the two-true-leaf stage was found to be an adequate method for determining pathogenicity of Rhizoctonia isolates, and is less time-consuming than the method currently used.