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Light induced resistance to bacterial gall disease caused by Pseudomonas syringae pv. cerasicola in cherry tree (Cerasus × yedoensis)

Makoto Ishihara: Forestry and Forest Products Research Institute, Hokkaido Research Center

<div>A bacterial gall disease of cherry trees caused by <em>Pseudomonas syringae</em> pv. <em>cerasicola</em> leads to a twig blight and decline. <em>Cerasus</em> ×<em> yedoensis</em> is resistant to this pathogen, but is often infected under dark light conditions; therefore, the resistance to bacterial gall disease in <em>C. </em>×<em> yedoensis</em> is thought to be light induced. Inoculation experiments to <em>C. × yedoensis</em> were conducted under various light conditions of light intensity, light quality, and irradiation times using with fluorescent tubes in growth chambers. High light intensity, long irradiation time, and blue light irradiation caused to reduce gall size. We assessed histological and anatomical features of diseased regions to evaluate the effect light intensity and quality on disease development. The inoculated branches treated with medium or weak white light intensity developed bigger galls than those treated with high intensity white light or medium intensity blue light. In the weaker white light conditions, cell death spread across the branch and the large galls developed due to the increased number of callus cells. In the high light treatments, a small region of the gall cortex died and its size remained small, indicating that the pathogen was confined by the hypersensitive reaction of the plant. It was concluded that a light induces the resistance to a bacterial gall in<em> C. × yedoensis</em>. Further, we showed that the ultraviolet irradiation reduced a gall size on <em>C. × yedoensis</em> twig. It is suggested that the ultraviolet may contribute to the development of resistance of <em>C. × yedoensis</em> under field conditions.</div>