Evaluation of grapevines for resistance to downy mildew (Plasmopara viticola) under greenhouse conditions

Grapevine downy mildew, caused by the fungus Plasmopara viticola is a disease with a great economic impact on grapevine in the Brazil. The objective of this study was to evaluate resistance to downy mildew in seedless grapevine hybrids and one susceptible cultivar ‘Thompson Seedles’ using natural infection (cross-contamination) and artificial inoculation method under greenhouse conditions. The experiments were performed at Embrapa Semiarid, Petrolina, Pernambuco, Brazil. The first used natural infection from plants with diseased vines, and the second artificial infection in which plants were sprayed with a spore suspension with a concentration of 10 5 conidia mL −1 . The evaluated variables were final incidence, final severity, area under the curve of disease incidence progression and area under the curve of disease severity progression. All evaluated genotypes showed symptoms of downy mildew. The CPATSA 28.14 genotype presented the lowest values of final severity, final incidence, area under the disease severity progress curve and area under the disease incidence progress curve in both experiments. Therefore, the CPATSA 28.14 genotype was identified as having greater resistance to grapevine downy mildew. Clustering by the unweighted pair grouping method using arithmetic averages (UPGMA) resulted in the separation of the genotypes into three and two similarity groups in Experiments I and II, respectively, indicating low diversity among the grapevine hybrids evaluated.