การคัดกรองและเตรียมสูตรสำเร็จของรา Trichoderma spp. เพื่อควบคุมโรคใบจุด Curvularia ของกล้าปาล์มน้ำมัน

Abstract

Leaf spot disease caused by Curvularia oryzae is a severe outbreak on oil palm seedlings in nurseries. Long-time usage of chemical fungicide not only causes pathogen resistance but also harmful for human health and environment. The use of antagonistic microorganism is an alternative strategy but it is inconvenient to use. In this study, fungi were screened for antagonistic activity against C. oryzae and developed to emulsifying biopesticide. Twenty-six isolates of fungi were isolated from the tissue and leaf surface of oil palm leaves collected from Khlong Hoi Khong District and the agricultural field of Faculty of Natural Resources, Hat Yai District, Songkhla, and 2 isolates (Trichoderma harzianum TM2 / 1 and Streptomyces hygroscopicus NR 8-2) were obtained from the Culture Collection of Pest Management Depertment. Six isolates (V76-12, T76-1, V76-14, T76-14, T76-12/2 and T. harzianum TM2/1) showed antagonistic activity against the mycelial growth of C. oryzae with inhibition rate more than 80% on dual culture plate assay. The antagonists were identified into 2 species as follows: T. asperellum (T76-12 and V76-12) and T. spirale (V76-12, T76-1 and T76-12/2) by morphology characteristics and molecular techniques. Electron microscope observation showed that mode of action of the six isolates were covered and coiled around C. oryzae, while S. hygroscopicus NR 8-2 caused abnormal shaped of C. oryzae hyphal tip. T. spirals T76-1 and T. harzianum TM2 / 1 produced chitinase and beta-1,3-glucanase enzymes to degrade fungal cell wall and produced volatile (alcohol group) to inhibit mycelial growth of C. oryzae. Three isolates (T. harzianum TM2 / 1, T. spirals T76-1 and S. hygroscopicus NR 8-2) induced the activities of the plant defense enzymes including polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia lyase (PAL). Therefore, these isolates were selected to develop to emulsion formulation. In efficiency test showed that all formulations, storage at 10°C increased the shelf-life in comparison with room temperature. In nursery experiments, the 4 formulations showed effective in reducing disease incidence which did not significantly differ from chemical fungicide (prochloraz).