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

(Seed Health Management for Better Productivity)4. Sheath rot:It is caused by Sarocladium oryzae. Sheath rot was observed during 1972 and 1973 inseveral states and its first occurrence in India was reported independently from Karnataka, AndhraPradesh, West Bengal and Tamil Nadu. Since then it has been reported from several other statesfrom Kerla, Orissa, Uttar Pradesh, Bihar, Punjab and Rajasthan. The pathogens attack the uppermost leaf sheath enclosing the young panicles. It causes total sterility, chaffiness and nonemergenceof panicles resulting in loss in grain yield. On 0 to 9 scale, disease scores up to 3 didnot cause yield reduction but scores from 4 to 9 caused 3 to 80 % yield loss. Discoloration of riceseeds due to sheath rot pathogen has been observed. Qualities of rice grains are also affected.Seeds germination / protien content of grains are also reduced. (Vidyasekaran, 1989). Thepathogen survives for 4 months in seed and 10 months in leaf sheath in the field.Control Seed treatment with Benomyl or carbendazim reduce seedling mortality and improve seedgermination. Foliar sprays with carbendazim or propiconazole @ 0.1% is the effective treatment againstsheath rot.5. Bunt of RiceThe disease occurs in most of the rice growing areas of the world (Agarwal et al., 1989). Ithas been reported in India from Andhra Pradesh, Andeman and Nicobar, Orissa, Punjab,Rajasthan and Tamil Nadu. The disease has potential to cause extensive yield loss to the crop. Itcaused about 15 million dollars loss in the Texas region in the USA (whitney and Fredrikesen,1971) and up to 87% panicle infection has been reported from Pakistan (Hassan, 1971). In India,10-15% infection has occurred in Assam, 0.75-18.5% in Tamil Nadu, up to 27% in Orissa, 0.1-22.5% in Karnataka, 0.2-1.6% in Andaman and Nicobar islands and 30% in Rajasthan(Chowdhary, 1951: Widespread occurrence and up to 80% incidence (infected panicles) of thedisease have been observed in 1997 in the Punjab State.The disease is found in the field at the time of maturity of the rice crop. Only a few grainsin a panicle are infected. Normally only a part of the grain is affected but many a times the entiregrain may be replaced by black powdery mass of bunt spores. The infected seeds often showgreenish black discoloration, which can be detected during visual observation of the seed lot.Minute black pustules or dots can be seen on the glumes. In severe infections rupturing glumesshow beak- like out growths. When the smut balls burst open, the black powdery mass of the buntspores scatter on to the other seeds or leaves. Some times, the infected grains may be detectedby their dull color before the glumes burst open. Most often, in the field, the infected grains exhibitno external symptoms.The seed-borne bunt inoculum poses a serious threat for widespread distribution ofdisease in rice growing regions. The partially or completely infected grains may not be easilydetected visually in seed lots. This may escape the notice of workers. Association of bunted seeds- 157 -