Rice leaf blight, also known as the disease caused by *Bipolaris oryzae*, is a widespread issue in rice-growing areas across the country. The disease can affect rice plants from the seedling stage all the way to harvest. It primarily damages above-ground parts of the plant, especially the leaves. When seeds are infected, the coleoptiles turn brown, and the buds fail to emerge. The cotyledons may also wither. In the seedling stage, lesions on the leaves and sheaths appear as elliptical spots, similar in size to flax seeds, dark brown in color, and sometimes they expand into long stripes. These lesions often lead to death of the affected tissues.
In adult plants, the disease initially appears as small brown spots on the leaves, which gradually grow into elliptical lesions resembling sesame seeds. The center of these lesions turns brown or gray, while the edges remain dark. A yellow halo often surrounds the lesions, and in severe cases, irregular, large spots form. The affected leaves dry out from the tips, turning brown. Black fungal growth (conidia and spores of the pathogen) develops on dead seedlings. Lesions on leaf sheaths begin as oval, dark brown spots with water-soaked margins that later develop into irregular, larger spots with a central brownish area. Infected panicle necks and branch stems become dark brown, leading to premature drying of the ears. Early infection of grains can spread to full grains, causing grain discoloration and reduced quality. In later stages, lesions are smaller and less distinct, and the infected grains become brittle.
When humidity is high, a black fungal layer forms on the diseased parts, consisting of conidiophores and conidia of the pathogen. The pathogen, *Bipolaris oryzae* (formerly *Helminthosporium oryzae*), belongs to the genus *Deinophyta*. Its conidiophores are 2–5 in bundles, unbranched, slightly curved, and septate. They are terminal, decumbent, or cylindrical, ranging from 24 to 122 μm in length, with 3–11 septa. This fungus is an ascomycete and is found only in culture, not under natural conditions.
The disease spreads through overwintering mycelium in infected plant debris or on seeds. Conidia can survive for 2–3 years in dry conditions, while latent mycelium can persist for up to 3–4 years. Mycelium in the soil loses its viability after one winter. Infected seeds can introduce the pathogen to new fields, where conidia are dispersed by wind and rain. Germinating hyphae can directly penetrate the host or enter through stomata. High temperature, high humidity, and fog promote disease development. Acidic soils, sandy soils, phosphorus deficiency, and potassium deficiency increase susceptibility. Dry fields can also favor the disease.
The optimal temperature range for mycelial growth is 5–35°C, with the best growth occurring at 24–30°C. Conidia formation occurs between 8–33°C, with 30°C being ideal. Spore germination requires temperatures between 2–40°C, with 24–30°C being most favorable. Germination needs water droplets, and relative humidity must exceed 92%. Under saturated humidity at 25–28°C, spores can infect the host within 4 hours.
To manage the disease, it is important to reduce the source of inoculum by properly disposing of infected straw. Use certified disease-free seeds or disinfect them if necessary. Apply well-decomposed compost as a base fertilizer, and supplement with phosphorus and potassium, particularly potassium, which enhances plant resistance. Improve drainage in acidic soils and apply lime if needed. Avoid prolonged flooding and use shallow irrigation to maintain good air circulation. Chemical control measures are similar to those used for rice blast disease.
Dehydrated Broccoli,Dehydrated Broccoli For Seasoning,Dehydrated Broccoli For Snacks,Dehydrated Broccoli Powder
Taizhou Shubenshu Food Co.,Ltd , https://www.lvweifoods.com