Plant Resistance Inducers Affect Multiple Epidemiological Components of Plasmopara viticola on Grapevine Leaves

Abstract

Plant resistance inducers (PRIs) harbor promising potential for use in downy mildew (DM) control in viticulture. Here, the effects of six commercial PRIs on some epidemiological components of Plasmopara viticola (Pv) on grapevine leaves were studied over 3 years. Disease severity, mycelial colonization of leaf tissue, sporulation severity, production of sporangia on affected leaves, and per unit of DM lesion were evaluated by inoculating the leaves of PRI-treated plants at 1, 3, 6, 12, and 19 days after treatment (DAT). Laminarin, potassium phosphonate (PHO), and fosetyl-aluminium (FOS) were the most effective in reducing disease severity as well as the Pv DNA concentration of DM lesions on leaves treated and inoculated at 1 and 3 DAT; PHO and FOS also showed long-lasting effects on leaves established after treatment (inoculations at 6 to 19 DAT). PRIs also prevented the sporulation of Pv on lesions; all the PRI-treated leaves produced fewer sporangia than the nontreated control, especially in PHO-, FOS-, and cerevisane-treated leaves (>75% reduction). These results illustrate the broader and longer effect of PRIs on DM epidemics. The findings open up new perspectives for using PRIs in a defense program based on single, timely, and preventative field interventions.

Infection Risk-Based Application of Plant Resistance Inducers for the Control of Downy and Powdery Mildews in Vineyards

“…In fact, the labels of the commercial products we used include DM only as the target disease. In this study, PHO and FOS effectively reduced PM incidence on leaves and bunches and showed similar disease severity control as the other PRIs known to protect plants against PM [20,40,42,58,61]. Rantsiou, et al [60] and Moine, et al [62] also documented the efficacy of PHO against E. necator in a vineyard study.…”

“…We also shifted from a calendar to a risk-based application by using mathematical models to predict potential infection by P. viticola and E. necator, as well as the residual efficacy of a previous fungicide treatment. By using weather forecasts, model predictions anticipated the possible risk so that treatments were applied preventatively, 1-3 days before an infection prognosis, as we suggested in previous studies [41,42]. In those studies, we evaluated disease and sporulation severity following the artificial inoculation of leaves collected from PRI-treated vineyard plants with P. viticola sporangia [41] or E. necator conidia [42] at 1-19 or 1-12 days after treatment (DAT), respectively.…”

“…By using weather forecasts, model predictions anticipated the possible risk so that treatments were applied preventatively, 1-3 days before an infection prognosis, as we suggested in previous studies [41,42]. In those studies, we evaluated disease and sporulation severity following the artificial inoculation of leaves collected from PRI-treated vineyard plants with P. viticola sporangia [41] or E. necator conidia [42] at 1-19 or 1-12 days after treatment (DAT), respectively. The results clearly showed that PRIs can be used preventatively, with the highest efficacy at 3-6 DAT, depending on the product.…”

“…LAM is a water-soluble polysaccharide that consists of β-(1-3)-glucan derived from the brown alga Laminaria digitata [74], which has been previously shown to control both DM and PM [22,23,37], and to efficiently reduce infection by P. viticola and the production of sporangia on DM lesions, with prompt and long-lasting activity [41]. CER is a yeast-derived PRI made of purified cell walls of Saccharomyces cerevisiae strain LAS117 that has been found to effectively reduce DM [18,19,75] by mobilizing plant defense reactions that are more effective against P. viticola than E. necator [76].…”

“…In previous studies, we evaluated the pre-infection efficiency of some commercial PRIs on P. viticola [41] and E. necator [42] under vineyard conditions. Plants were sprayed once with PRIs and the leaves were inoculated with the pathogen at 1 to 19 days after PRI treatment.…”