Seed Health Management for Better Productivity - Govind Ballabh ...

(Seed Health Management for Better Productivity)glumes, hilum and placenta. It is also observed on pericarp and in the endosperm. At the time ofseed germination the fungus grows from hilum through pericarp to the extruded tip of the scutellumor epiblast to the coleoptile and then to the first leaf.Several epiphytotics of the disease have been recorded in different parts of the world,resulting in serious losses in yield. In korea, it is the only rice disease that has ever caused aserious problem. The loss in yield during 1953, an epidemic year, was estimated at about 800,000tons in Japan. Yield losses were estimated at over 90% in Bicol during 1962 and at 50-60% inLeyet during 1963, in the province of Philippines. In India, epiphytotics have been reported in theTanjore area of Madras state in 1919. In the hills blast may cause more than a 65% loss in yield.Control Treat the seed with Thiram + carbendazim (1:1) @ 3.0 g/ kg or Beam @ 4 g/ kg. Early plantings have less disease than late plantings. Seedlings raised in upland nurseries are more susceptible to blast even after transplanting. Close spacing also often increase the severity of the disease. Controlled irrigation waterreduces damage from blast. Foliar sprays with carbendazim or Hinosan @ 0.1% in nursery, at maximum tillering stage andat 50% flowering stages to check neck blast. Single spray of Beam @ 600g/ha checks thedisease development at all stages of plant growth.2. Brown spotIt is caused by Dreschslera oryzae. The fungus infects at all the growth stages of the crop.On leaves oval, light to dark brown lesions are produced which join each other and kill the leafprematurely it causes discolouration of grain at flowering stage and shriveling of kernel. Thedisease is mainly seed-borne and causes seedling blight in cooler region.Symptoms appear as lesion (spots) on the coleoptile, leaf blade, leaf sheath, and glumes,being most prominent on the leaf and glumes. The lesions are brown at first, and later becometypically ellipsoidal, oval to circular measuring about 0.5-22mm x 2-5mm. At maturity, they have alight brown or grey center with a dark or reddish brown margin. Larger lesions are typical of moresusceptible cultivars. On the coleotile, the spots are brown and small, whereas on the glumes theyare dark brown to black in colour with olivaceous velvety growth. In severe infection, the wholegrain surface becomes blackened and the seeds are shriveled and discolored.Seedlings are often heavily attacked with numerous lesions about 2.5 mm in diameter andin such cases, leaves may dry out and ultimately die. Badly affected nurseries can often berecognized from a distance by their brownish, scorched appearance, although seedlings areusually not killed by the disease. Brown spot infection has been found to cause grain yield lossesup to 29 per cent and seed rot up to 37.3 per cent. The disease is primarily seed borne butprimary infection is likely to be severe only when the soil temperature at the sowing time is below26 0 C. Black spots appear on glumes. Poor germination of infected seeds has been reported. Dueto general weakening of plants, shriveled and poor settings of seeds are common. Disease- 155 -