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Abstract, Thesis, 2003

A preliminary survey on occurrence of dry root-rot disease associated with sweet orange (Citrus sinensis Osbeck) was carried out in Ananthapur, Nalgonda and Prakasam districts of Andhra Pradesh. The disease incidence varied with area and it was in the range of 8.8 to 24.1 per cent. Among the three districts surveyed, mean dry root-rot incidence was high (21.4%) in Prakasam district followed by Ananthapur (17.2%) and Nalgonda (9.75%). Among the 17 isolates of Trichoderma, only TCT4 and TCT10 isolates grew 78 and 77 mm within 48 h and were categorised as very fast growing. In dual culture, Trichoderma isolates TCT4, TCT10 and bacterial isolate TCB (P1) inhibited the test pathogen Fusarium solani more effectively than the others. In morphological characters all the 17 isolates have shown considerable variation. Molecular characterization of Trichoderma isolates revealed the presence of proteins of molecular weight 22, 29 and 43 kDa in most of the isolates. In pot culture experiment, effective native Trichoderma spp. (TCT4), Pseudomonas spp. TCB(P1) along with organic amendments neem cake and farm yard manure (Treatment T10 ), applied at the rate of 100g/kg of soil reduced the dry root-rot disease effectively upto 81.67 per cent over control.