Estimation of the impact of leaf scorch on photosynthesis and "physiological-lesion" size in strawberry

Abstract

The impact of strawberry leaf scorch, caused by Diplocarpon earlianum, on net CO2 assimilation (A) and transpiration (E) rates was determined for both greenhouse- and field-grown plants. In the greenhouse, strawberry (Fragaria ×ananassa) plants were inoculated with an aqueous suspension of D. earlianum (1 × 105 conidia/mL) and placed in environmental conditions to generate a range of disease severities. Photosynthesis measurements on individual leaflets of greenhouse-grown plants ('Kent') were taken in a biotron under saturating light conditions. Photosynthesis was also measured on leaflets in a naturally infected field planting of 'Jewel' in 2003. Leaf-scorch severity ranged from 0% to nearly 100% on individual leaflets. Strong negative linear correlations were found between the proportion of leaflet area with visual symptoms and A, E, and water-use efficiency (WUE = A/E). "Physiological-lesion" size was estimated to be 1.6 and 2.1 for greenhouse-grown and field-grown plants, respectively, meaning that the total area of leaflet tissue affected by leaf scorch was 1.6-2.1 times larger than the leaflet area showing visual symptoms of the disease. The larger physiological lesion found in field-grown plants may be due to field-associated stress factors or cultivar variability. The results have application for establishing guidelines for the management of foliar diseases of strawberry.