การพัฒนาชีวภัณฑ์จากสเตร็พโตมัยซีสเพื่อควบคุมโรคใบไหม้ของมะเขือเทศ

Abstract

Potato late blight has a very high impact on yield in both quality and quantity of tomato producing in Thailand. Fungal pathogen, Phytophthora infestans that has long life period to survive in soil and infected plant debris. Difficulty to use fungicide for controlling the disease has been a limitation in harvesting period their risk for pesticide residues in the product. Therefore, objectives of this study select the antagonistic microbe and develop to bioproduct for controlling late blight disease. Firstly, 36 isolates of Streptomyces group obtained from the plant pathology laboratory Faculty of Agriculture, Chiang Mai University were selected from their efficiency in inhibiting the pathogens. It was found that Streptomyces albus CEN26 isolate has 89.33% effective in inhibiting mycelium growth, reducing the disease incidence by 90.39% and growth-promoting effects on tomato plant in tissue culture and greenhouse conditions. Subsequently, the appropriate liquid medium testing for S. albus CEN26 inoculum production was conducted and found that ISP-S liquid media was the best to produce 109 cfu/ml of the spore suspension after culturing for 5 days. When used to produce dry spore mass by applying biofilm culture using different ratios of stock culture and fresh medium, the results of the ratio 1:4 was suitable to produce 1010 spores per plate after culture for 7 days. Biofilm culture filtrate was also found at approximately 5 ml/plate. The efficacy of biofilm culture filtrate to control late blight pathogen was investigated in this study. Inhibition of P. infestans, mycelial growth, germination, and viability of the sporangia were evaluated, and found that the minimum concentration of the filtrate which effectively 100.00% inhibited the fungus was 60%. The filtrate concentration at 40% resulted in significant inhibition of the fungal mycelial growth and sporangia viability at lower rates than the 60% trials, though, it still extremely inhibited the sporangia germination in all incubation period trials. Even though, the concentration at 20% had no effect on sporangia viability but clearly restrained its germination period. The proper formula would be selected by the bio-product powder properties, losses, fine, dry, water-soluble, vital spore concentration, and ability to inhibit the disease. Results presented that bio-products have the best properties and are qualified for controlling late blight disease. The bio-product was formulated using carrier substances composed of Lactose, sodium carboxymethyl cellulose, sodium bicarbonate, and citric acid. The efficiency of disease control in the greenhouse and field condition of bio-product produced from biofilm culture filtrate mixed with dried spores and bio-product produced from dry spores only were compared. The disease control trial in greenhouse conditions using bioproducts produced from biofilm culture filtrate combined with dry spore showed reductions in both percentages of disease incidence and severity index better than the trial of bioproducts produced from only the dry spore. Then, bioproduct produced from biofilm culture filtrate combined with the dry spore was selected to apply in farmer plot trial, by spraying 10 g/20 L once a week for 4 months, the disease reduction was found with a percent of disease incidence and severity index revealed at 25.45% and 45.63%, while the untreated farmer plot was determined at 52.30% and 75.45%, respectively.