Filtrados de cultivo dos fungos sapróbios Curvularia inaequalis e Stachybotrys globosa no controle biológico de doenças e na indução de resistência em videiras cvs. Isabel e Cabernet Sauvignon

Abstract

This work aimed at evaluating the effect of culture filtrates of saprobe fungi Curvularia inaequalis (CUI) and Stachybotrys globosa (STG) on the management of leaf diseases: mildew (Plasmopara viticola), anthracnose (Elsinoe ampelina) and Isariopsis leaf spot (Isariopsis clavispora); on the incidence and severity of mildew in grape bunches; on the induction of resistance in grapevines cultivar Cabernet Sauvignon and on the physicochemical characteristics of grapes, cultivar Isabel, treated during pre-harvest on the first year (August 2011 - December 2011) and in commercial vineries in Marialva, PR and Maringá, PR, from February through June 2012. We also assessed the effect of culture filtrates on bioactive compounds and antioxidant activity of grapes, cultivar Isabel. The treatments were: 0, 1, 5, 10 and 20 mL.L-1 of culture filtrates of saprobe fungi CUI and STG. In addition, the standard treatments we used as control were: Bordeaux mixture and Mancozeb mix and the alternative treatments we used were acibenzolar-S-methyl and Agaricus blazei. The incidence and severity of diseases in grapevine leaves and fruit were determined by visual assessments, based on diagrammatic scales for further determination of the area under disease progress curve (AUDPC). The induction of resistance was determined by the activity of enzymes related to host defense (peroxidase, catalase, polyphenoloxidase and phenylalanine ammonium liase). Productivity was determined by counting the number of grape bunches per plant, bunch weight, total soluble solids (SST -Brix), total titratable acidity (ATT %), ratio, pH, productivity per plant (g), and juice yield (%). Postharvest quality was analyzed by determining fresh mass loss, berry dropping, weight of dropped berries, antioxidant capacity, anthocyanin content, phenolic compound content, flavonoid content, must-bearing pulp color and grape skin color. In field conditions, during both years, both culture filtrates were effective in reducing mildew and Isariopsis leaf spots in the leaves of plants cultivated in Marialva, PR, as well as in reducing the severity of mildew in grape bunches, especially in higher concentrations (10 and 20 mL.L-1 of filtrate). However, in periods when climate conditions are more favorable for pathogen development and the inoculate pressure is high, the efficiency was lower. Similar results for both filtrates and years of study were observed for the control of anthracnose in Maringá, PR. Therefore, these filtrates are not recommended for mildew control in grapevines (both leaves and bunches) in areas with high inoculate pressures and periods with high humidity and average temperatures. In postharvest, the grape bunches showed no adverse chemical alterations upon submission to these products; however, their physical characteristics were compromised. In postharvest conservation, CUI and STG filtrates, when applied before harvest, at 10 and 5 mL.L-1, respectively, were effective in improving the levels of antioxidant activity in 83 and 63%, total polyphenol content in 151 and 109 mg GAE.100g-1 and flavonoids in 8 and 8 mg.100g-1, respectively. On the other hand, they were not as effective with fresh mass loss, dropping and mildew incidence in grape bunches, which increased as time went on. Thus, further study is necessary.