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

(Seed Health Management for Better Productivity)1996). Sharma et al., (1987) observed that seed treatment with Derosal, Emisan and Thiram wereeffective in improving germination of discoloration seeds.8. Bacterial Leaf BlightBacterial leaf blight caused by Xanthomonas oryzae pv. oryzae is said to have been firstseen by farmers in the Fukuoka area of Japan in 1884. The disease has been reported fromPhilippines, Korea, USSR, China, Indonesia, Taiwan, Mexico, Thailand, Bangladesh, Nepal,Pakistan, Latin American Countries, Niger and West Africa, and Ukraine. The disease was firstreported in India by Srinivasan et al. in 1959 from Maharashtra, where it was widespread anddestructive since 1951. The disease appeared in an epiphytotic form in Shahabad district of Biharin 1963 on variety BR-34 (Srivastava and Rao, 1963). After the introduction and cultivation over alarge acreage of new high yielding but susceptible rice cultivars, the disease has become one ofthe most serious problems on rice in India (Ou, 1972).Reductions of 20-30 percent have been observed in grain yields when infectionwas moderate and over 30 per cent when it was severe. A loss of about 47-75 per cent in yieldhas been reported in artificially inoculated crop. Bacterial leaf blight caused yield losses up to 50per cent in paddy field. The loss in yield has been attributed due to increase in chaffiness,decrease in grain weight and number of panicle. As a result of reduction in the number of filledgrains in diseased panicle, a loss in weight of 20.38 per cent was obtained In assessing the effectof X. oryzae, 33.2 per cent more chaffy glumes and reduction in 1,000 grain weight were recordedin infected tillers than in healthy tillers. At IRRI, Philippines, losses in yield were 74.89 and 46.88 percent in IR-1 and Taiwan-8, respectively.It has been observed that the bacterium commonly present in the husk and endosperm ofthe grains. Survival of Xoo in the seed varied depending on the environmental conditions underwhich seeds were stored. Under low temperature and low humidity Xoo does survive for more then6 months, where as under high humidity and temperature survival was found much shorter. Abilityof seeds to transmit the disease to new plants has been reported by several workers. In China,seed transmission is the main source of inoculum in field. Srivastava et al (1967) observed thatseed was able to carry the Xoo when planted following year. Seed transmission was foundnegative in India, Japan and Philippines, where high humidity and warm temperature do existseed transmission does not play important role in transmission to new field.Symptoms appear as yellow or straw coloured wavy water soaked stripes beginning from oneor both margins covering the whole leaf blade which dry premature. Lesions may develop on anyportion of leaf blade or on the mid rib. Small orange coloured beads may be seen in early morningduring wet nights. These are the bacterial exudates which further spread the disease when mixedwith rain water. Kresek phase is characterized by drying or wilting of the whole plant and may beobserved during early growth stage of rice plants up to 4-6 weeks after transplanting. Theinfection becomes systemic and spreads through out the plant. The leaves roll inwardlongitudinally along the midrib with dull green water soaked lesions on them followed by drying of- 163 -