Evaluating Strawberry Host Plant Resistance to Macrophomina Root Rot

Strawberries are a $2.9 billion crop in California, supplying 90% of total U.S. production in 2023. However, susceptibility to soilborne pathogens such as Macrophomina phaseolina poses a serious economic threat to production. Preplant soil fumigation is the main control strategy used in California for all soilborne pathogens, but this strategy faces challenges due to increased fumigant regulations. Hence the need for alternative disease management tactics. During the 2023 and 2024 season, host plant resistance evaluations for Macrophomina root rot were conducted at California Polytechnic State University, San Luis Obispo. Both experiments included 63 strawberry cultigens (defined as cultivars and elite breeding lines) from multiple breeding programs. Of the 63 cultigens, 35 were common to both years. All plants were exposed to the pathogen via artificial inoculation two weeks after planting. In 2023, plant mortality for all cultigens ranged from 5.1% to 81.3% with an average of 38.0% and in 2024 the range was 6.5% to 58.8% with an average of 27.9%. For the cultigens common to both years, average plant mortality decreased from 36.8% in 2023 to 28.3% in 2024. Differences in plant mortality between years were likely influenced by year to year variation in environmental conditions, including temperature, chill accumulation, and plant water stress. Annual screening of strawberry cultigens for Macrophomina root rot is essential to assess the susceptibility of both new and existing cultigens under changing environmental conditions.