Influence of leaf scorch on vegetative growth and yield of three strawberry (Fragaria × ananassa Duch.) cultivars with differing levels of resistance

Abstract

Three strawberry cultivars, Kent, Jewel and Blomidon, were evaluated for their reaction to leaf scorch (Diplocarpon earlianum) disease. The three cultivars are considered to be susceptible, moderately resistant and resistant to leaf scorch, respectively. Plants were grown in the field in a runnerless culture system and inoculated with conidial suspensions at one of five concentrations to generate a range of disease severities. The control plants were not innoculated. Disease severity was monitored during the establishment year and these data were used to calculate area under the disease progress curves (AUDPC) for each cultivar. At dormancy, vegetative growth analysis was performed on a sample of plants from each plot. The remaining plants were overwintered and data were collected on yield and yield components the following season. The difference in AUDPC values between control and highest levels of the disease for Kent, Jewel and Blomidon were 31.6, 26.0 and 25.2 units, respectively. Leaf scorch reduced photosynthetically active leaf area in all three cultivars, which reduced dry matter accumulation. The vegetative characters most affected were leaf area and number, crown number and dry weight and root dry weight. At the highest level of disease attained total yield declined 58, 41 and 31 g plant-1 corresponding with disease severities of 44.5, 36.4 and 32.4 units AUDPC for Kent, Jewel and Blomidon, respectively. This represented a 20–21% yield reduction in each cultivar. Fruit number was the yield component most sensitive to the leaf scorch disease. A strong relationship was established between highest disease severity during late summer and fall (which includes the time of flower bud initiation) and yield the following season. Key words: Diplocarpon earlianum, foliar disease, June-bearing