Chua sahet kan thamhaikoetrok lae patikiriya khong phan oi to rok baichutwongwaen.
1991
Supranee Boonsathorn
Grading system for disease severity index (DI) of 1 to 5. By using this system sugarcane varieties were grouped into 3 groups, i.e., 23 varieties were resistant with DI 1.0-2.0, 24 varieties were moderately resistant with DI 2.1-3.0 and 200 varieties were susceptible with DI 3.1-5.0. The appropriate leaf area for evaluating disease severity was 20 square cm which gave similar result to the use of 40-100 square cm. Pathogenicity test conducted by inoculating the sugarcane leaf with mycelial disc containing a pathogenic fungus revealed that variety CP64-388 was the most susceptible whereas BO14, PL310 were less susceptible with necrotic areas of 6.1 and 2.1 square mm, respectively. The highest metabolite production from L. sacchari was obtained by culturing the fungus in potato dextrose broth at room temperature for 21 days. Purification of fungal metabolites by column chromatography indicated that fraction number 6a caused the largest necrotic spot on sugarcane leaf. Further purification of fraction number 6a by Thin layer chromatography revealed that spot number 2 gave the largest necrotic spot. The disease symptoms caused by fresh culture of L. sacchari were similar to those caused by its metabolites, however, variation in sizes of the lesions was found to be due to the sugarcane varieties. Screening for resistance by using crude metabolites on 12 sugarcane varieties revealed the largest necrotic lesions found on F166 and Pindar while PL310 showed the smallest one. In addition, the metabolite produced from L. sacchari induced necrotic lesion on leaves of 19 different plant species, therefore this metabolite could be classified as non-specific toxin. The metabolite may be applicable for the selection of resistant sugarcane varieties to ring spot.
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