Methods for detection of soilborne pathogens affecting strawberry in Israel.
In Israel, strawberry is a winter producing crop cultivated as a fresh cropping system. Nuclear and foundation propagation material are indexed for viruses and checked for fungal pathogens twice annually, while spring-propagated field nurseries are monitored routinely for disease until summer transplanting to production fields. Various wilt pathogens affect the crop at different stages of propagation, however, the most vulnerable is at the field nursery stage where mother and daughter plants are exposed to outdoor, adverse conditions. Soilborne fungi such as Colletotrichum spp., Phytophthora spp., Rhizoctonia spp., Verticillium dahliae, Fusarium spp. and Macrophomina phaseolina are pathogens of the crop in Israel. Wilted plants are routinely sampled in the field by farmers and extension specialists from the Ministry of Agriculture and pathogens detected in the laboratory in Volcani Center. Initially, infected plant tissues were plated on selective medium for Phytophthora spp. and Fusarium spp., semi-selective medium for Colletotrichum spp. and V. dahliae, and non-selective PDA medium for Rhizoctonia spp. and M. phaseolina. Cultures isolated from the different media were inspected microscopically for morphological characters typical for the causal agent of disease. Colletotrichum and Phytophthora were further differentiated to the respective species (C. acutatum and C. gloeosporioides) and (P. cactorum and P. fragariae) according to specific-primer PCR amplification. Although Fusarium spp. were isolated in high numbers during the years 2005-2007, the predominant pathogen isolated from wilted plants during that period was M. phaseolina. A future research program based on pathogenicity tests and molecular gene sequences will determine whether the Fusarium spp. isolates are pathogenic to strawberry.