鎂肥施用對水稻之稻熱病及生長的影響

Abstract

水稻 (Oryza sativa L.) 是臺灣重要的糧食作物，在整個生育期間皆可能感染由風、水及植株種子傳播Magnaporthe oryzae引起之稻熱病，為水稻主要的真菌性病害。稻熱病傳播速度快且易造成流行病，感染植株各部位，染病植株會因產生灰綠色及白色病斑而減少葉片光合作用面積，嚴重時使水稻產量降低。因此，控制稻熱病病徵擴散是臺灣水稻栽培管理的重要課題。鎂是葉綠素的中心元素，參與許多植物生理代謝反應。過去的研究指出，施用高濃度鎂肥雖然無法直接抑制病原菌入侵植物體內，但藉由增加鎂以提高葉片葉綠素濃度，透過光合作用的增強，進而減緩真菌造成之水稻紋枯病及雲紋葉枯病病徵擴大。然而，目前關於施用鎂肥對於減緩稻熱病病徵擴大及對水稻植株生長的影響之研究仍然不足。因此，本研究透過盆栽水耕試驗種植水稻（台南11號），並接種稻熱病菌及施用 0.27 mM 及 0.54 mM 濃度之鎂肥，以無添加鎂肥作為對照組，檢測葉綠素濃度及抗氧化酵素，以探討不同鎂肥濃度對於稻熱病的抑制效果。試驗結果顯示，有接種病菌處理之 0.27 mM 濃度鎂肥處理的株高、鮮重、葉綠素總量及地上部植體鎂含量最高，而抗氧化酵素活性在 0.27 mM 濃度處理時最低，但丙二醛濃度卻是最高的。再者，透過盆栽土耕試驗，葉面噴施 20 mM、40 mM 及 80 mM 鎂肥，結果發現，接種病菌後，水稻葉綠素總量在 40 mM 處理時降低，與未接種病菌處理有顯著 (p < 0.05) 差異，而 80 mM 鎂肥處理的葉綠素總量、抗氧化酵素活性、及丙二醛皆與接種前沒有顯著差異。有葉面噴施鎂肥之過氧化酶活性明顯高於無添加鎂肥處理。未來建議能依不同土壤性質進行鎂肥施用，以降低農藥使用量，維護生態平衡及維持作物產量與品質。

Rice (Oryza sativa L.) is the most important staple crop in Taiwan. Blast is one of the destructive fungal diseases of rice caused by Magnaporthe oryzae, via the transport by wind, water, and seed during the whole growth stage and can easily cause epidemic. Various organs of the rice plant can be infected by the spores, while reducing the photosynthetic area due to the development of gray-green and white lesions, and further results in yield losses. Magnesium (Mg) is the core atom of chlorophyll, involved in various physiological metabolisms in plants. Past studies have shown that, even though Mg did not directly inhibit the penetration of pathogens into the plants, the application of high concentration of Mg fertilizer increased the chlorophyll concentration in rice leaves, by increasing foliar Mg concentration, which increased the ability of the photosynthesis and consequently decreased the sheath blight and the leaf scald symptoms caused by fungal Rhizoctonia solani and Monographella albescens. However, the effects of Mg fertilizer application on the rice blast disease remains unclear. Thus, this study aims to explore the impact of Mg on delaying the expansion of blast disease symptoms and rice growth by conducting hydroponic cultures of rice variety Tainan 11 with inoculating the spores of Magnaporthe oryzae and applying Mg fertilizer at 0.27 mM and 0.54 mM, with a treatment without Mg fertilizer serving as the control. Additionally, the inhibitory effects of different Mg fertilizer concentrations on rice blast disease will be evaluated by measuring chlorophyll concentration and antioxidant enzymes. The experimental results showed that, among the inoculated treatments, the 0.27 mM magnesium treatment exhibited the highest plant height, fresh weight, total chlorophyll content, and shoot magnesium concentration. Moreover, antioxidant enzyme activities were lowest in the 0.27 mM treatment, which may have indirectly led to an increase in malondialdehyde (MDA) concentration. Additionally, foliar sprays were applied Mg fertilizer at concentrations of 20 mM, 40 mM, and 80 mM in pot experiments. After pathogen inoculation, total chlorophyll significantly decreased in the 40 mM treatment compared to the non-inoculated treatment (p < 0.05). However, in the 80 mM treatment, total chlorophyll, antioxidant enzyme activity, and MDA did not differ significantly in inoculation treatment. Peroxidase activity was significantly higher (p < 0.05) in applying Mg fertilizer plants compared to 0 mM treatment, suggesting the activation of a protective mechanism against disease stress. These findings suggest that Mg fertilizer application could be adjusted according to soil properties, thereby reducing the use of pesticides for maintaining ecological balance and ensuring crop yield and quality in the future.