Detecting negative effects of fungal wood pathogens in Vitis vinifera prior to symptoms expression
Authors:Jerome Pouzoulet, Philippe Rolshausen, Victoria Woods
- Louis Santiago, Associate Professor of Physiological Ecology, University of California, Riverside
- Alexandria Pivovaroff, Ph.D. Candidate, University of California, Riverside
Fungal wood pathogens cost millions of dollars each year to the California grape (Vitis vinifera) industry. These fungi, such as Phaeomoniella chlamydospora and Neofusicoccum parvum, infect the wood of grapevines impairing water and nutrient translocation, which leads to a slow decline and death of the plant. However, different grape cultivars (cvs.) express different levels of resistance to these pathogens. Understanding the mechanisms of resistance is important for possible prevention or ease of these losses. We are investigating through greenhouse studies whether effects of these fungi can be detected prior to symptom expression by measuring eco-physiological traits following initial wood infection in one susceptible (Thompson) and one resistant (Merlot) cultivar. We hypothesized that inoculated individuals would exhibit decline in stomatal conductance (gs) and dark-adapted photosynthetic yield (Fv/Fm) over time, while individuals of the control would not. In addition, we hypothesized that the more susceptible cv. would show decline sooner or to a greater degree than the less susceptible variety. For each cv., 5 individuals were inoculated with P. chlamydospora, 5 with N. parvum, and 5 kept as the control. We measured gs and Fv/Fm pre-inoculation, and post-inoculation every 2-3 weeks. Pre-inoculation Fv/Fm indicated that all individuals started out healthy. Three months after inoculation, results showed no significant difference in gs between control and inoculated groups for either variety with either fungi. In addition, there was no difference in Fv/Fm between control and inoculated groups of Thompson. However for Merlot, control plants actually had a lower Fv/Fm than plants inoculated with P. chlamydospora, though values for all groups are still in the ‘healthy’ range (Fv/Fm > 0.75). Lack of divergence in gs between control and inoculated groups and healthy Fv/Fm values for all groups indicates that we need to further monitor these plants as these fungi take several months to cause disease.