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

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 O-2(-) 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.