Development of a reliable screening technique for determining tolerance to Macrophomina phaseolina in strawberry

Abstract

Macrophomina phaseolina is a typical soilborne fungal pathogen causing crown and root rot in strawberry (Fragaria × ananassa Duch.) worldwide. M. phaseolina has become a major problem for strawberry growers parallel to the phase-out of methyl-bromide since 2004 and is considered the most destructive soilborne pathogen of strawberry since then. Global warming is characterized by extreme weather conditions, in the Mediterranean area, as reflected by long, hot, dry summers without rain and relatively short, cold rainy winters. This together with regulatory restrictions on toxic fumigants creates favorable conditions for M. phaseolina to thrive. Screening for resistant germplasm is currently the most effective and sustainable approach for managing the disease. In order to screen for susceptible/tolerant strawberry cultivars, various inoculation techniques were assessed on five strawberry cultivars. Artificial inoculation of growth medium with naturally infected plant material and the use of the ‘toothpick’ method resulted in no significant differences. However, the use of artificially produced sclerotia in a soil mix at concentrations of 2.5 × 103 sclerotia/g soil exhibited differential cultivar mortality rates. High variation was found among 32 tested strawberry varieties (Israeli and US) grown under outdoor conditions in a screenhouse. Cultivars ‘Pelican’ (US), ‘Orly’, ‘Tamir’ and ‘Rotmy’ were considered tolerant compared to cultivars ‘Florida 90’ (US) and ‘Peles’ that were the most susceptible. The overall results indicate that the choice of certain Israeli and US cultivars may provide future germplasm for resistance breeding against M. phaseolina.