Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2007
Publication Date: 3/22/2007
Citation: Turechek, W., Heidenreich, C., Lakso, A., Pritts, M. 2007. Photosynthesis and estimation of virtual lesion size of Strawberry leaves infected with Diplocarpon earliana. Canadian Journal of Plant Pathology. 29:159-165. Interpretive Summary: Leaf scorch is one of the most important diseases in commercial strawberry production. The disease causes dead spots to appear on the surface of the leaves. In general, growers believe that strawberry can compensate for high levels of leaf disease after harvest, such that flower bud formation is affected minimally, resulting in a negligible reduction in yield in the subsequent year. Results of this study demonstrated photosynthesis and water use were reduced in proportion with increased leaf scorch. Interestingly, the reduction in photosynthesis and water use was 1.6 – 2.1 times larger than could be accounted for by the area of the leaf covered by dead spots. Thus the apparently healthy portions of leaves with spots also had reduced rates of photosynthesis and water use. The results of this study show that the effect of the disease is greater than it might appear to the unaided eye and has a greater impact on plant health than what growers might typically perceive. These results will be of interest to scientific researchers and are also useful for establishing guidelines for initiating control tactics against strawberry leaf scorch.
Technical Abstract: The impact of strawberry leaf scorch disease, caused by Diplocarpon earlianum, on net CO2 assimilation (A) and transpiration (E) was determined for both greenhouse and field grown plants. In the greenhouse, plants were inoculated with a 1 x 105 conidial suspension of D. earlianum and placed under various conditions to generate a range of disease severities. Photosynthesis measurements of greenhouse-grown plants (cv. Kent) were made in a biotron under saturating light conditions, and also in a naturally-infected field planting of ‘Jewel’ in 2003. Disease severity ranged from 0 to nearly 100%. A strong negative linear correlation between rate of CO2 assimilation, water use efficiency (WUE=A/E) and percent infected leaf area was found. 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 leaf tissue affected by leaf scorch was 1.6 to 2.1 times larger than the leaf area showing visual symptoms of the disease. The larger physiological lesion found in field-grown plants is likely due to the additional stresses experienced there, compared to a greenhouse. The results of this study are useful for establishing guidelines for initiating control tactics against foliar diseases of strawberry.