Grapevine abiotic stress induce tolerance to bunch rot

Abstract

Context. Botrytis bunch rot occurrence is the most important limitation for the wine industry in humid climate viticulture. Previous studies of our group showed strong differences in bunch rot incidence between floor management treatments: cover crop (CC) vs weed-free strips under the trellis with herbicide (H). We observed that in some circumstances this reduction in bunch rot incidence occurred without major vine growth differences among treatments. The aim of the present study was better understanding the factors involved in this differential response observed.

Materials and methods. The experiment was conducted over two growing seasons in southern Uruguay (34°44′ S, 56°13′ W). Ninety-six plants of Vitis vinifera (Tannat), grafted on to SO4 rootstocks, grown in 100 L pots were used each season. The four years old vines were trained on vertical shoot positioning system (VSP) located inside an experimental vineyard. We tested the effect and interactions of soil management treatments and grapevine water status (irrigation schedules) on grapevine tolerance to disease development. Treatments were arranged in a split-plot randomized block design with 6 replications, whit cover crop schemes as main plots and water availability during pre-veraison period as subplots. Cover crop treatment (CC), consisting of full cover of the plot soil with tall fescue versus bare soil (H). Main plots, comprising 16 adjacent vines. Supplementary irrigation was applied daily to maintain equal water status during the entire growing season regardless soil management treatment. In no water stress treatment (NWS) irrigation thresholds were −0.5 MPa MDSWP until fruit set, −0.6 MPa from fruit set to veraison and −0.8 MPa from veraison to harvest. The same thresholds were used for water stress (WS) treatment except for the period of 20 days previous veraison were plants were not irrigated until reach −1.1 MPa MDSWP.

Results. Bunch rot incidence and severity were remarkably lower in CC compared to H treatments while water restriction during perversion period also reduce significatively bunch root incidence. The results were consistently significant both seasons even when vegetative expression, PAR% at the fruit zone, cluster size and compactness and fruit composition were comparable among treatments. Our results do allow us to affirm that other factors besides vegetative expression/bunch compactness, and fruit zone environment, are playing an important role on the disease development.