大蒜水萃液對水稻紋枯病的防治效果評估

Evaluation of control effect of aqueous garlic extract on rice sheath blight

水稻是臺灣最重要的糧食作物，其種植面積與產值皆為農作物之冠。在水稻生產過程中，立枯絲核菌（Rhizoctonia solani）AG-1 IA引起的水稻紋枯病（rice sheath blight, ShB）為最主要的病害之一，一旦爆發將嚴重影響水稻的產量與品質。目前防治水稻紋枯病的方法普遍依賴化學農藥，但長期大量使用化學農藥有污染環境及危害人畜健康的風險，且可能導致病原體產生抗藥性。相較之下，天然植物保護資材具有對人畜毒性低、殘留量少、對病害作用獨特等優勢，能有效防治病蟲害且不易產生抗藥性。因此，本研究旨在開發簡易的大蒜（Allium sativum L.）（品種為和美蒜）水萃液（aqueous garlic extract）製備方法，並評估其在以下三方面的應用：1.對水稻紋枯病菌的抑菌效果；2.儲存條件；3.對水稻紋枯病的防治效果。透過這些評估，提供一個安全有效的植物源防治資材替代化學農藥的選擇。根據試驗結果顯示，使用10 g大蒜與50 mL無菌水所製備的大蒜水萃液（原液），能夠抑制水稻紋枯病菌菌絲生長達79.78%。將原液稀釋兩倍、或將大蒜與無菌水依等比例放大水量（使用200 g大蒜與1000 mL無菌水）時，其抑制率分別為58.09%和46.54%。在儲存方面，大蒜水萃液原液儲放效果最佳，於-20℃儲存28天後仍具有50.99%的抑菌率。儘管於25℃和4℃儲存之大蒜水萃液抑菌效果降低，但仍有超過45.93%的抑菌率。大蒜水萃液對菌核發芽抑制效果試驗之結果顯示，大蒜水萃液原液之抑菌率可達92.95%，與施用濃度為150μg/mL（150 ppm）之市售大蒜素水溶液效果相近。本研究試驗亦使用不同重量的大蒜（1、3、5、7及10 g）製備大蒜水萃液，噴施於水稻上後，防治水稻紋枯病的效果與大蒜水萃液中大蒜含量成正比，分別為31.35%、57.06%、79.18%、80.85%及84.76%。相較之下，噴施150 ppm的大蒜素水溶液之對照組J. Plant Med.Vol. 65 No. 3, 2023 115DOI:10.6716/JPM.202309_65（3）.0004對水稻紋枯病的防治率可達94.88%。綜合上述結果，本研究所評估之大蒜水萃液具有非農藥防治水稻紋枯病、降低糧食損失的潛力，可作為防治水稻紋枯病的替選方案。

Rice is the most important food crop in Taiwan, with the largest planting area and output among all crops. In the process of rice production, rice sheath blight (ShB) caused by Rhizoctonia solani AG-1 IA is one of the major diseases, which can seriously affect rice yield and quality once it breaks out. Currently, the prevention and control of ShB rely mainly on chemical pesticides, but long-term and large-scale use of chemical pesticides has the risk of polluting the environment and harming human and animal health, as well as potentially leading to pathogen resistance. In contrast, natural plant protection products have advantages such as low toxicity to humans and animals, low residue, and unique effects on diseases and pests, which can effectively control pests and diseases and are less likely to develop resistance. Therefore, this study aims to develop a simple method for preparing aqueous garlic extract and evaluate its applications in three aspects: 1. inhibitory effect on ShB pathogen; 2. storage conditions; 3. prevention and control of ShB in rice. According to the experimental results, the aqueous garlic extract prepared from 10 g of garlic and 50 mL of sterile water (undiluted solution) can inhibit the growth of R. solani, the causal agent of rice sheath blight, by 79.78%. When the undiluted solution was diluted two-fold or the amount of garlic and sterile water was increased proportionally (using 200 g of garlic and 1000 mL of sterile water), the inhibition rates were 58.09% and 46.54%, respectively. In terms of storage, the undiluted aqueous garlic extract showed the best preservation effect, with a 50.99% inhibition rate after 28 days of storage at -20°C. Although the inhibition effect decreased when the garlic extract was stored at 25°C and 4°C, it still showed inhibition rates of over 45.93%. The results of the germ tube inhibition test showed that the undiluted aqueous garlic extract can inhibit germ tube growth by 92.95%, which is similar to the effect of a commercially available garlic extract solution at a concentration of 150μg/ml (150 ppm). In addition, the efficacy of the garlic extracts in controlling rice sheath blight was proportional to the amount of garlic used (1, 3, 5, 7, and 10 g). The inhibition rates were 31.35%, 57.06%, 79.18%, 80.85%, and 84.76%, respectively. In comparison, the control group treated with 150 ppm garlic extract solution showed a disease control rate of 94.88%. Based on the comprehensive evaluation results, the evaluated aqueous garlic extract has the potential to be used as a non-pesticidal alternative and reduce food loss for controlling rice sheath blight.