UV-B RADIATION FOR CONTROL OF STRAWBERRY POWDERY MILDEW

Powdery mildew of strawberry (Fragaria × ananassa) caused by Sphaerotheca aphanis var. aphanis is one of the serious airborne diseases in Japan. We have used various methods in an attempt to control this disease. Among these methods, liquid potassium silicate was found to be a very useful liquid fertilizer for suppressing powdery mildew. However, various types of cultivating style are used in strawberry production, and it is difficult to apply the silicate using each cultivating type. Recently, we focused on the use of UV-B radiation as an alternative method of disease control. Many reports have described how UV-B induces plant resistance against many stresses. However, there are no examples of its practical application in horticulture. In the present study, radiation conditions were determined in order to prevent the disease in an experimental booth. The suppressive effect of UV-B radiation against powdery mildew was evaluated in a vinyl house from October to June using three susceptible cultivars: ‘Akihime’, ‘Toyonoka’, and ‘Sachinoka’. All cultivars were protected from powdery mildew by UV-B radiation. For example, in ‘Akihime’ control plots, 41% of fruits were diseased, whereas in the UV-B plots, 0% of fruits were diseased. Similar results were obtained for the other cultivars. In a laboratory experiment, RT-PCR analysis revealed that UV-B radiation induced the expression of a disease-resistance gene (the gene encoding the PR-protein). These results indicate that UV-B prevents powdery mildew development by inducing disease resistance in the plants as one of its modes of action.