Acquired resistance of rice leaves to Rhizoctonia solani [India]
1986
Kalaiselvi, K. | Sreenivasaprasad, S. | Manibhushanrao, K. (University of Madras, Madras (India). Centre of Advanced Studies in Botany)
Sheath blight (Sh B) incited by Rhizoctonia solani is a major fungal disease of rice. Acquisition of Sh B resistance in excised rice leaves has been worked out through prior interaction with an avirulent R. solani isolate. In leaves preinoculated with R7, Sclerotia of the virulent isolate did not spread until 72 h and formed only a few lesions, for 90% protection. The generally slow-growing avirulent isolate R7 showed neither antibiosis nor parasitism and was overgrown by R5 in dual culture. Histopathological studies revealed sparse growth of R7 at the site of inoculation, with inability to produce infection cushions on rice leaves. Direct penetration of the mycelium through either stomata or cuticle was not observed. The fact that 60-65% protection against Sh B could be obtained even when leaves were challenge-inoculated where R7 had not spread (2-3 cm away) rules out direct antagonism between the 2 RS isolates and any competitio0779n for entry, colonization, and leaf exudates. Activatiion of host defense mechanisms might be responsible for acquired resistance. Preinoculation of rice leaves (prior interaction) with R7 successfully induced protect
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