Can grapevine tolerance to bunch rot be directly induced by groundcover management?

Abstract

Context and purpose of the study – Botrytis bunch rot occurrence is the most important limitation for the wine industry in humid environments. The effect of grapevine vegetative growth on bunch rot expression results from direct effects (cluster architecture, nitrogen status among others) and indirect ones (via microclimate). 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 to test the general hypothesis that other factors unrelated to grapevine vegetative expression could be more relevant to grapevine susceptibility to bunch rot.

Materials and methods – The experiment was conducted over two consecutive growing seasons in southern Uruguay (34°44′ S, 56°13′ W). Twenty plants of Vitis vinifera (Tannat), grafted on to SO4 rootstocks, grown in 100 L pots were used each season. Vines were trained to a vertical shoot positioning system (VSP) in north-south oriented rows (0.6 × 2.8 m, vine (pot) × row spacing) located inside an experimental vineyard. We tested two treatments: Cover crop (CC), consisting of full cover of plot soil with Tall fescue (Festuca arundinacea) versus weed-free pots, treated with herbicide (H). Supplementary irrigation was applied twice a week as needed to maintain equal water status during the entire growing season regardless of treatment. In order to minimize effects of treatments related to vine vigor, treatments were arranged interspersed in the row and the “arms” of contiguous plants were overlapped. To enhance cluster size and compactness variability, half of each plant was spur pruned, and cane pruned at the other side (2 two buds spur + 8 buds cane).

Results – Bunch rot incidence and severity were remarkably lower in CC compared to Herbicide treatments even when vegetative expression (Vine PW, cane PW, PW/m), PAR% at the fruit zone, cluster size and compactness and fruit composition (TSS, titratable acidity, pH) were comparable among treatments (H vs CC). Our experiment allows to compare the effect of the treatments, when clusters shared the same environment minimizing the effect of other factors such as primarily inoculum or microclimate. Our results do not allow to identify the specific mechanism by which CC induced a greater tolerance to bunch rot. However, it is possible to affirm that other factors besides vegetative expression/bunch compactness, and fruit zone environment, are playing an important role on the disease development.