BENZOTHIADIAZOLE INDUCES DEFENCE RESPONSES IN BERRY CROPS

Abstract

Plants have developed multiple protection strategies during evolution in response to invading pathogens and environmental stresses. Flavonoids are a large and diverse group of over 4000 compounds, many of which are known to play an important role against UV-light stress and microbial attacks in plants. Many of these plant defence compounds are also health-promoting phytochemicals in the human diet. Strawberry (Fragaria x ananassa) contains a variety of such phenolic compounds. We found that the most disease resistant (to gray mold) strawberry cultivar contained considerably more flavonoids than the most susceptible one, but the role of these compounds in disease resistance is still unclear. Defence mechanisms in plants can be activated by biotic or abiotic elicitors, which trigger a defence pathway leading to the expression of several defence genes and the accumulation of antifungal compounds, which eventually leads to the inhibition of the fungal growth. We tested the ability of benzothiadiazole (BTH) to induce resistance to powdery mildew (Sphaerotheca macularis) in strawberry. Powdery mildew has become a serious disease in strawberry grown in greenhouses in many parts of the world. As chemical control is difficult because of the rapid development of fungicide-insensitive strains, alternative strategies are needed. We showed that foliar applications of BTH (0,6-1,2 g/l) on young strawberry leaves provide effective mildew control in greenhouses. The flavonol glycoside content of BTH-treated leaves was also analyzed by HPLC and ESI-MS method, but no clear differences were detected between BTH-treated and control plants. However, the levels of two flavonols, quercetin and kaempferol, in berries were increased in response to foliar treatments under field conditions. The results suggest that BTH and related bioactivators may become a realistic alternative for chemical control against powdery mildew in strawberries grown in greenhouses and plastie tunnels.