The trade-off between grape yield and grapevine susceptibility to powdery mildew and grey mould depends on inter-annual variations in water stress
Résumé
tReducing plant growth to limit their susceptibility to diseases has been proposed as a way to reducepesticide use, but reducing crop growth may have detrimental effect on yield. In this paper, we test thehypothesis of a trade-off between maintaining grape yield and reducing grapevine susceptibility to pow-dery mildew (Erysiphe necator) and grey mould (Botrytis cinerea), two major diseases of the grapevine(Vitis vinifera L.). Grapevine susceptibility to these two diseases was measured by relevant features ofgrapevine vegetative development identified in previous studies: leaf biomass at flowering for powderymildew and pruning mass for grey mould. Data were collected during a 3-year field experiment in a vine-yard located in the south of France, in which pests and disease were controlled by spraying pesticides. Thetwo pathogens studied in this paper were chosen because they differ in terms of their biology (biotrophvs necrotroph) and their interaction with the grapevine (the highest grapevine susceptibility occurs earlyin the cycle for powdery mildew and late in the cycle for grey mould), in order to give genericity to theresults. Results confirmed the hypothesis of a trade-off between maintaining grape yield and reducinggrapevine susceptibility to both pathogens through reduced vegetative growth, but provided evidencethat win–win situations (high yield, low susceptibility) do exist. Moreover, we found a synergy betweenreducing grapevine susceptibility to powdery mildew and grey mould. These results suggest opportuni-ties to reduce fungicide use when a win–win situation occurs as the risk of yield and quality losses maybe lower in those years. Inter-annual variation in water stress at flowering was found to be a key driverof the balance between grape yield and grapevine susceptibility to both pathogens through their effecton the source–sink balance of the grapevine. Water stress at flowering appeared as a relevant indicatorto inform the probability of occurrence of a win–win situation. Our results suggest that it could also beused to adapt management practices like irrigation, cover cropping or a combination of both, to reacha win–win situation. The relevance of these findings to vineyards in similar semi-arid environments is discussed.