Vitis species and varietal resistance of mature berries against inoculation of an isolate of the Colletotrichum acutatum complex that causes grape ripe rot

Grape ripe rot, caused by several Colletotrichum species, is one of the main grapevine diseases, favored by warm and humid climates, attacking mainly white grape cultivars. It directly affects the quality of the wine and does not have a satisfactory solution, not even with the use of fungicides. Equally relevant are the growing restrictions on production systems that are intensive in chemical inputs, due to environmental impacts and human health. Thus, it is necessary to develop selection criteria for use in breeding programs aimed at developing cultivars that combine disease resistance genes and enological quality. In this context, the objective of this work was to evaluate the pathogenicity and aggressiveness of an isolate of Colletotrichum acutatum in berries of different grapevine genotypes with different forms of inoculation. Inoculated berries from Vitis vinifera cultivars and partially resistant cultivars (PIWI) containing downy mildew resistance alleles (Rpvs) were evaluated. All white and rose grape cultivars were susceptible to the C. acutatum isolate. The cultivars ‘Bronner’, ‘Souvignier Gris’, ‘Sauvignon Blanc’, ‘Calardis Blanc’ and ‘Helios’ showed a higher degree of susceptibility, while ‘Felicia’ and ‘Poloskei Muskotaly’ showed lower susceptibility than the other white grapes cultivars. As expected, red cultivars ‘Regent’, ‘Prior’ and ‘Merlot’, showed a low degree of susceptibility. Wounding the skin also increased the penetration of the fungus into the pulp in some cultivars. Without any signal of infection, berries from V. shuttleworthii behaved as highly resistant. The results indicate that there is genetic variability for resistance to Colletotrichum within existing cultivars and further studies are needed to identify other resistant genotypes and possible resistance alleles to all the fungi species that cause the ripe rot disease in grapes.