Exogenous Calcium Improved Resistance to Botryosphaeria dothidea by Increasing Autophagy Activity and Salicylic Acid Level in Pear

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Pear ring rot, caused by Botryosphaeria dothidea, is one of the most serious diseases in pear. Calcium (Ca2+) was reported to play a key role in the plant defense response. Here, we found that exogenous calcium could enhance resistance to B. dothidea in pear leaves. Less H2O2 and O2− but more activated reactive oxygen species scavenge enzymes accumulated in calcium-treated leaves than in H2O-treated leaves. Moreover, the increased level of more ascorbic acid-glutathione was maintained by Ca2+ treatment under pathogen infection. The expression of core autophagy-related genes and autophagosome formations were enhanced in Ca2+-treated leaves. Silencing of PbrATG5 in Pyrus betulaefolia conferred sensitivity to inoculation, which was only slightly recovered by Ca2+ treatment. Moreover, the salicylic acid (SA) level and SA-related gene expression were induced more strongly by B. dothidea in Ca2+-treated leaves than in H2O-treated leaves. Taken together, these results demonstrated that exogenous Ca2+ enhanced resistance to B. dothidea by increasing autophagic activity and SA accumulation. Our findings reveal a new mechanism of Ca2+ in increasing the tolerance of pear to B. dothidea infection.