High night temperature promotes downy mildew in grapevine via attenuating plant defence response and enhancing early Plasmopara viticola infection

The night temperature is one of the critical environmental factors affecting the grape berry quality. The objective of this study was to clarify whether a high night temperature promotes downy mildew on grapevines. The high night temperature conditions suppressed the gene expression of the pathogenesis-related proteins in the grapevine cultured cells and grapevine seedlings compared with the control night temperature conditions. The Plasmopara viticola colony formation on the leaves of the seedlings exposed to the control night temperature conditions became slightly noticeable on day 5 after inoculation, whereas a large number of colonies were clearly observed on the leaves of the seedlings exposed to the high night temperature conditions. On day 10 after inoculation, the leaf defoliation and withering were marked in the P. viticola infected seedlings exposed to the high night temperature conditions. The high night temperature conditions promoted the P. viticola zoospore germination. These results suggest that the high night temperature promoted the grape downy mildew by attenuating the constitutive plant defence re­sponse as well as enhancing the P. viticola early infection. Viticulturists should be vigilant regarding pest management strategies against the P. viticola primary infection of grapevines when high night temperatures continue for a long time.