สูตรสำเร็จของจุลินทรีย์ปฏิปักษ์เพื่อควบคุมโรคใบจุดของผักสลัดในระบบไฮโดรโปนิกส์สำหรับการค้า

Abstract

Leaf spot disease of lettuce (Lactuca sativa L.) in hydroponics system caused by Corynespora cassiicola and Curvularia aeria, causing reduction of both quantity and quality for lettuce cultivation in Songkhla province. Controlling diseases using chemicals fungicide is unsuitable and can cause human health risks. As lettuce is often consumed as a fresh vegetable, biological control is an appropriate way to control leaf spot disease. However, the use of fresh antagonistic microorganisms was limited according to the preparation process and the short shelf life. This research aimed to select the effective antagonistic microorganisms to control leaf spot disease of lettuce in hydroponics systems caused by C. cassiicola and C. aeria. Six isolates of Trichoderma spp. namely T. asperellum T1, T76-14, T. harzianum TM2/1, T. spirale T76-1, T76-12/2, V76-12, and Streptomyces angustmyceticus NR8-2 were obtained from Culture Collection of Pest Management, Prince of Songkla University. Primary screening of antagonistic microorganisms by dual culture assay showed two isolates (T1 and T76-1) were effective in inhibiting mycelial growth of fungal pathogens with 80-95% inhibition. Volatile compounds emitted by both isolates inhibited mycelial growth of pathogens with 30-45% inhibition, and Gas chromatograph mass spectrometer profiling revealed the presence of antifungal compounds including alcohol, ester and pyran. Trichoderma T1 and T76-1 produced and released extracellular B-1,3-glucanase and chitinase into culture medium to degrade fungal cell wall. Spore suspension of T1 and T76-1 were effectively reduced the disease severity index (%DSI) of leaf spot disease in lettuce seedlings with 55-65%. In addition, inoculation of T1 and T76-1 induced the defense response in lettuce seedlings by producing defense-related enzymes such as B-1,3-glucanase, chitinase, polyphenol oxidase (PPO) and peroxidase (POD). Therefore, both T1 and T76-1 were selected to develop in different formulations composed of wettable powder, granules, encapsulated granules and emulsion. The results showed emulsion formulation with coconut oil and soybean oil based was effective in inhibiting mycelial growth of C. cassiicola and C. aeria more than other formulations. For all formulations, storage at 10 °C extended the shelf-life in comparison with storage at room temperature. In field experiment, application of emulsion formulation in concentration 3% significantly (P ≤ 0.05) reduced the diseases severity index caused by the 2 pathogens at 29-40%, compared with other treatments. This formulation is suitable to control leaf spot disease of lettuce and to develop for the commercial purpose in the future.