Occurrence, Virulence, Inoculum Density and Plant Age of Sclerotium rolfsii Sacc. Causing Collar Rot of Peppermint

Roving survey was conducted during 2011-2012 around Coimbatore, Dindigul, Erode, Hosur, Krishnagiri, Namakkal, Salem and Theni districts to assess the incidence of collar rot of peppermint. The maximum incidence of 32.33% was recorded in Therkupalayam village of Coimbatore District. The pathogen was isolated from infected samples and 8 Sclerotium rolfsii isolates were maintained. The level of pathogenicity of these isolates revealed that S. rolfsii (I 1 ) from Therkupalayam in Coimbatore District was the most virulent and caused higher levels of collar rot incidence (93.66%). An inoculum load of S. rolfsii at 5% to 1 kg of soil registered the maximum incidence of 92.66% collar rot of peppermint. Significantly higher per cent of wilting of 92.66% was recorded in plants at 20 days after emergence and it was found significantly more susceptible compared to rest of the treatments.