Effect of Cultivar and Temperature on Disease Development of Macrophomina Root Rot in Strawberry

Root rot, or charcoal rot, caused by the soilborne fungus Macrophomina phaseolina, is a significant disease affecting strawberry production worldwide. Field trials were conducted for five seasons (2016-2017 to 2020-2021) to evaluate strawberry host plant resistance to Macrophomina root rot (MRR) in California. A wide range of plant resistance to MRR was observed. Because low disease severity occurred in the fifth season, a summary of the first to fourth seasons showed that 'Osceola' was highly resistant, whereas 'Festival', 'Sweet Ann', and 'Ruby June' were highly susceptible. Disease severity varied over the seasons for specific cultivars, as did the average final mortality for all cultivars. Models were built to investigate the relationship between environmental variables and final disease mortality among the seasons. Strong positive associations were found between the soil temperature during the first month after planting (R2 = 0.79, P < 0.0001) or air temperature mid-season (R2 = 0.79, P < 0.0001) and the final disease mortality of eight cultivars. We concluded that the soil temperature during the early stage of plant development and the mid-season air temperature are important factors in disease development for MRR. Screening new strawberry cultivars and elite breeding lines against MRR should be ongoing as part of a standard process for determining the susceptibility of currently grown and potentially new cultivars.