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Root rot of groundnut caused by Macrophomina phaseolina causes significant losses in groundnut growing areas of Tamil Nadu. Hence, the present study was conducted to assess the prevalence and incidence of dry root rot of groundnut in different district of Tamil Nadu, India during 2013-14, assess the cultural characters and pathogenic variability among the isolates of M. phaseolina and to test the antifungal activity of water extracts from mangrove plants against pathogen. The results revealed that the maximum root rot incidence was observed (30.33%) in Sivapuri village of (I 3 ) Cuddalore district. The disease incidence was more in, VRI2 variety and incidence was found to be more in sandy loam soils. Regarding the cultural characteristics revealed that the isolates I 2 and I 3 significantly recorded the maximum (90 mm) mycelial growth of M. phaseolina and the isolate I 3 was found to be more virulent when compared to other isolates tested. Water extracts of nine mangrove plant species were screened against the root rot pathogen, M. phaseolina. Of these, Salicornia brachiata (21.33 mm), Rhizophora apiculata (23.00 mm) and Suaeda maritima (26.33 mm) were found to be highly effective against the test pathogen.

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.

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