Biological Control of Root Rot of China Aster
Ten fungi and one bacterium were isolated consistently from the rhizosphere of China aster (cv. Local) plants and their population was gradually increased from seedling to vegetative and vegetative to flowering stages. In vitro screening of rhizosphere microflora, exotic and commercial formulations of fungal and bacterial antagonists against Rhizoctonia solani, Trichoderma viride (Native Tv1), T. harzianum (DOR Th), Pseudomonas fluorescens (ANGRAU Pf1) and Bacillus subtilis (NBAII Bs) were found to be the best among all the isolates tested in inhibiting the growth of the test pathogen. The compatibility of fungal and bacterial antagonists was tested with eight fungicides and it was observed that T. viride (Native Tv1) was compatible with validamycin, T. harzianum (DOR Th) with carbendazim, P. fluorescens (ANGRAU Pf1) with thiophanate methyl and B. subtilis (PDBC Bs) with iprodione+carbendazim (Quintal) at their recommended and half the recommended dosages. The efficacy of potential antagonists (Native Tv1, DOR Th, ANGRAU Pf1 and NBAII Bs) and compatible fungicides (validamycin, carbendazim, thiophanate-methyl and Quintal) alone or in combination as seed treatment or soil application were evaluated for the management of R. solani causing root rot in China aster. The effectiveness of these antagonists increased when used as soil and seed application treatments and also when combined with soil drenching chemicals. Combined soil application of talc based formulation of ANGRAU Pf1 @2g/kg of soil and thiophanate methyl (0.1%) was found to be superior by recording significantly high per cent germination and least root rot incidence of 16.7 per cent. The antagonist P. fluorescens when used singly or combined with fungicide did not significantly affect the root rot incidence.