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

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(Seed Health Management for Better Productivity)pink discoloration (tanaka and Tsuchiya, 1987). Prevalence of low temperature has been shown tofavour infection by Phyllosticta glumarum, Epicoccum hyalopes and Magnaporthe grisea (Padwick,1950; Suryanarayan, 1958). Ray (1993) suggested that maximum seed discoloration occurs duringwet season when rainfall and relative humidity are high. Dash and Narain (1988) reported highincidence of glume discoloration by several fungi in wet as well as dry seasons at some places dueto low temperature, which predisposes the crop to fungi.Seed discoloration also increases with the increasing levels of nitrogen and phosphaticfertilizers (Misra an Dharam Vir, 1992). Ayotada and Salako (1980) reported that the rainfedwetland conditions and unbalanced nitrogen, phosphorus and potassium application favours seeddiscoloration. Application of silica increased total seed weight and effectively reduced seeddiscoloration (Yamauchi and Winslow, 1987; Korndorfer et al., 1999). Yamauchi and winslow(1989) reported that application of silica and magnesium protected rice plants against seeddiscoloration and seed yield increased by an average of 34 per cent. A higher seed infection anddiscoloration was rerecorded when older seedlings were transplanted as compared to youngseedlings and discoloration was more in transplanted crop as compared to direct sown crop (Misraand Dharam Vir, 1992).In West Africa, coarse upland soils and free draining soil water regimes increased seeddiscoloration severity while lowland soils and water saturation minimized it (Dobson and Aluri,1990). Late sowing, wider plant spacing (20x25cm), less nitrogen fertilization, application ofchemical fertilizers in combination with cattle manure decrease the seed infection as well as seeddiscoloration (Muhammad Saifulla et al., 1995; Mathew, 1996).ControlRice varieties/germplasms such as Improved White Ponni, Mahsuri, Intan Gowri, Prakash,ADT 39 (IR8xIR20), RAU 4045-2A (Fine Gora x IET 2832), Panikoili,, CTH 4, IET 11220, CTH 3,IET 10131, IET 10626, CTH 1, IET 11221 and Mangala were found resistant against seeddiscoloration (Prasad and Tomar, 1989; and Muhammad Saifulla, 1996).Seed treatment with different fungicides has been tried to reduce seedborne inoculum.Singh and Kang (1992) found that seed treatment with Thiram + carbendazim controlled seed rotand improved germination. Seed treatment with tricyclazole (0.2 per cent), carbendazim (0.2 percent) and mancozeb (0.3 per cent) gave effective control of P. grisea and B. oryzae (Geetha andSivaprakasam, 1993). Hetty and Shetty (1987) reported that paddy seeds treated with aqueousextracts of stem bark, leaf and seed of Strychnos nux-vomica effectively inhibited the developmentof Dreshlera oryzae, Trichoconiela padwickii, Alternaria alternata Nigrospora oryzae penicilliumspp. Curvularia sp and improved the germinability of the seeds.Fungicidal sprays of carbendazim, mancozeb at flowering stage and of Mancozeb andpropiconazole at boot leaf stage effectively controlled A.padwickii, C. lunata, C. oryzae, B. oryzae,F. moniliforme, F. pallidoroseum, C. pallescens, C. geniculata, C. eragrostidis, Nigrospora oryzaeand Trichothecium roseum causing seed discoloration (Sisterna and Ronco, 1994; Deka et al.,- 162 -
(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 -
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potential. An improvement in qualit
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9. Session Arrangement CommitteeDr.
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9. Dr. Pradip Kumar BorahSr. Scient
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TRAININGONANNEXURE-IIISEED HEALTH M
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ANNEXURE-IVCENTRE OF ADVANCED STUDI
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SundayApril 6MondayApril 7TuesdayAp
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TuesdayApril 15WednesdayApril 16Thu
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