Bacterial Blight of Rice and Its Control

Bacterial blight in rice, also known as white leaf mites, terrestrial fire, or thatch grass, is a serious disease that can affect the entire growing season. However, seedlings and tillering stages are most vulnerable. All plant parts can be infected, but leaves are particularly susceptible. The symptoms vary depending on the infection site, variety resistance, and environmental conditions, and are commonly categorized into three types. (1) Leaf Blight Type: This type primarily affects the leaves and leaf sheaths. The infection usually starts at the leaf tip or margin, with dark green, water-soaked linear spots forming first. These spots quickly develop into yellow-white lesions, which then spread along the leaf edges or midrib, turning brown and eventually drying up. Lesions have clear boundaries, while resistant varieties show irregularly wavy edges. Diseased leaves become gray-green, lose moisture rapidly, and develop blue-dry tissue, often appearing on upper leaves. (2) Acute Wilt Type: This occurs from the seedling to the tillering stage. Pathogens enter through wounds in the roots or stem base, causing rapid wilting. Affected plants lose water, their heart leaves turn black and die, while other leaves curl and the whole plant withers. The stems contain large amounts of bacteria, and some roots or leaf sheaths may appear yellow-brown. In certain cases, the flag leaf or lower leaves develop yellow midribs, leading to early death before heading. Brown necrotic bands may form under unfavorable conditions, slowing disease spread. (3) Jaundice Type: Rare and less common, this type shows early chlorotic spots on the heart leaves, followed by dry yellow spots. Water-soaked strips may appear at the base of diseased leaves. Under humid conditions or when morning dew is present, milky white dots are visible, which later form small yellow rubber particles. These particles easily fall off. Dead heart seedlings caused by bacterial blight typically appear during the tillering stage. Heart leaves or the second layer below show signs of dehydration, curling, and drying, eventually dying. As the disease progresses, other leaves shrink and the whole plant dries out. Peeling affected leaves reveals yellowish-white bacterial exudates, distinct from damage caused by pests like stem borers. Pathogen: The causal agent is *Xanthomonas oryzae*, including two pathovars: *pv. oryzae* and *pv. oryzicola*. Bacteria are short rods, 1.0–2.7 × 0.5–1.0 μm, single-flagellated, and Gram-negative. They produce yellow pigments and form viscous colonies. The optimal growth temperature is 25–30°C, with a range of 17–33°C. It thrives in pH 6.5–7.0. The bacteria infect cultivated and wild rice, and there are three serotypes, with Type I being widespread. Transmission: Primary sources include infected seeds, straw, and plants. Weeds can also act as carriers. Bacteria overwinter in seeds and enter through leaf holes or wounds. Wind, rain, irrigation, and human activities spread the disease. High humidity, heavy rain, and typhoons favor outbreaks. Excessive nitrogen fertilizer, poor drainage, and acidic soil increase disease risk. Control Methods: (1) Use resistant varieties suited to the local area. Examples include Jiayu 280, Japonica No. 61, Yuzao, and many others for early, mid, and late rice. Indica varieties such as DP5165, 95 Jian 27, and others are also effective. (2) Implement strict quarantine measures. Seeds should be soaked in 1% lime water or 80% 402 antibacterial agent diluted 2000 times for 2 days, or formalin solution for 3 hours. Soaking seeds in mycobiotin at 55°C for 36–48 hours is another method. (3) Apply compost and manage water levels carefully. Avoid waterlogging, drain after rain, and remove diseased straw and weeds. (4) Chemical control includes spraying 20% Ye Kuning (Ye Qing Shuang) at 100g/667m², or mixing with phytarctin if needed. Streptomycin or strong chlorine extract can also be used. Other options include chloramphenicol, Ye Shujing, and Yu-7802. Spraying mycinomycin or chlorobromoisocyanuric acid at 500 times dilution before transplanting helps prevent disease.

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