การควบคุมโรคเน่าสเคลอโรเตียมสาเหตุโรคหลังการเก็บเกี่ยวของมันฝรั่ง

Abstract

Potato sclerotium rot disease, caused by Sclerotium rolfsii, has a high impact on the postharvest quality of potato tubers during storage. Therefore, it has become a recurring problem to keep potatoes from the field, which has an infestation of this fungus. It’s soil–borne pathogens of plants that are very difficult to manage due to the rapid growth of mycelium and the production of many inoculums, which is a sclerotia. Thus, the objective of this study was to evaluate the efficacy of antagonistic bacteria, wood vinegar, and fungicides to control S. rolfsii causing sclerotium rot disease in potatoes under laboratory conditions. Heat-tolerant bacteria at 100°C were isolated by the serial dilution spread plate technique, which was isolated by 91 isolates. There are isolated soil samples in Chiang Mai Province, including 2 soil samples in agricultural areas, namely rice research field and vegetable field, and 3 soil samples in natural areas, namely Doi Suthep-Pui National Park Unit 4, Huay Jo reservoir, and Doi Pui viewpoint. All isolates of bacteria were tested for efficacy in inhibiting the mycelial growth of pathogenic fungi by the dual culture method. Bacteria were cultured on PDA before inoculation with mycelial of pathogenic fungi for 7 days. It was found that the bacterial isolates MH_15 and MJ_1 were significantly different. They inhibited mycelial growth by 98.67 and 84.45%, respectively. In addition, antagonistic bacteria from both isolates could produce secondary metabolites. The control of sclerotium rot disease was tested on potato tubers by immersion in bacteria suspension (MH_15 and MJ_1 isolates) at 108 CFU/ml concentration for 5, 15, and 30 min before inoculation of pathogenic fungi (pre-emergence) and 24 hrs. after inoculation of pathogenic fungi post-emergence). It was found that the efficacy of both antagonist bacteria was not significantly different both before and after inoculation. But the duration of immersion affects disease control. The immersion of 5 or 15 min was not statistically different. Potato tubers were immersed in the bacterial suspension of isolates MH_15 or MJ_1 for 5 minbefore inoculation. It’s most effective in controlling disease on tubers. The percentage reduction in the severity of the disease was 66.67 and 80.00%, respectively, compared with the other treatments. Identifying antagonist bacteria, namely MH_15 and MJ_1 by biochemical technique with the API 50CHB test kit, can be classified as Bacillus subtilis/amyloliquefaciens for both isolates. There is a similarity of 99.40%. The efficacy of wood vinegar in inhibiting mycelial growth and sclerotial germination of S. rolfsii was tested by the poisoned medium technique at 3 concentrations: 1.00, 2.00, and 3.00% (v/v). It was found that wood vinegar at 1.00% (v/v) concentration or more was able to inhibit mycelial growth and sclerotial germination by 100.00%, compared with the control treatment. When tested for controlling sclerotium rot disease on tubers using the immersion method in wood vinegar at four concentrations: 0.25, 0.50, 0.75, and 1.00% (v/v) for 5, 15, and 30 min before and after pathogenic fungi inoculation, it was discovered that the efficacy of wood vinegar in controlling the disease both before and after inoculation was significantly different. If tubers were immersed at a concentration of 1.00% (v/v) for 15 min before inoculation of pathogenic fungi, the severity of the disease could be reduced by 60.00%. However, immersion of tubers in wood vinegar at a concentration of 0.50% (v/v) for 15 or 30 min after inoculation is recommended. It was able to reduce the severity of the disease by 75.00% compared to the other treatments. The efficacy of six fungicides was tested at two concentrations, including half-recommended and recommended concentrations, using poisoned medium techniques. They’re divided into two categories: three contact fungicides, including captan (375 and 750 µg/mL), mancozeb (1,000 and 2,000 µg/mL), and etridiazole+quintozene (270 and 540 µg/mL). Azoxystrobin (25 and 50 g/mL), azoxystrobin+SHAM (25 and 50 g/mL + 100 g/mL (SHAM)), and difenoconazole (56.25 and 112.50 g/mL) were used to inhibit pathogenic fungal mycelial growth and sclerotial germination. It was found that six fungicides were significantly different. The contact fungicides such as mancozeb and etridiazole+quintozene at half-recommended and recommended concentration were able to inhibit the mycelial growth of pathogenic fungi by 100.00%, while captan at half-recommended and recommended concentration was able to inhibit the mycelial growth by 67.28 and 73.00%, respectively. In addition, it was found that the systemic fungicide, such as difenoconazole, at halfrecommended and recommended concentration, was able to inhibit the mycelial growth of pathogenic fungi by 100.00%, compared with the control treatment. The efficacy of fungicides in inhibiting sclerotial germination was tested. It was found that mancozeb and etridiazole+quintozene completely inhibited sclerotial germination at half-recommended and recommended concentrations. The efficacy of fungicides in inhibiting sclerotial germination was tested, and it was discovered that mancozeb and etridiazole+quintozene completely inhibited sclerotial germination at half-recommended and recommended concentrations, respectively, whereas captan inhibited sclerotial germination by 87.00 and 95.00%, respectively. Four fungicides, namely captan, mancozeb, etridiazole+quintozene, and difenoconazole, are effective in inhibiting mycelial growth by more than 70.00%. They were used to test the control of sclerotium rot disease on tubers by the immersion method in fungicides at recommended concentrations (750,2,000, 540, and 112.5 µg/mL, respectively) for 5, 15, and 30 min before and 24 hours after inoculation of pathogenic fungi. It was found that, the efficacy of all four fungicides in controlling the disease in pre-emergence and post-emergence stages was significantly different. In the case of pre-emergence disease, tubers were immersed in captan for 5, 15, and 30 min before inoculation. It had the most effective disease prevention. It was found that the percent reduction in severity of the disease was by 73.33, 100.00, and 66.67%, respectively, compared with the other treatments. However, in the case of post-emergence disease, tubers were immersed in each fungicide after 24 hrs. of inoculation. Immersion in three contact fungicides, captan, mancozeb, and etridiazole+quintozene, for 5, 15, and 30 min showed a percent reduction in disease severity but was not significantly different. Mancozeb was reduced in severity of disease by 100.00, 100.00, and 83.33%, respectively. In the case of etridiazole+quintozene, it was reduced by 100.00, 100.00, and 66.67 percent, respectively, and captan of all three periods showed a percent reduction in the severity of disease by 66.67%. Immersion of potato tubers in systemic fungicide (difenoconazole) for 5 and 15 min reduced disease severity by 100.00 and 75.00%, respectively.