Application of antagonistic microorganisms for the control of root rot of tangerine caused by Phytophthora parasitica (Dastur.)

During 24 mo. after the first application, populations of T. harzianum were 120-165 fold increased as compared with the control. For drenching of bacterial suspension, populations of bacteria in soil were increased as relative to the populations in natural soil without drenching (control). Most treatments with the broadcasting and drenching of antagonistic microorganisms caused the reduction of populations of Phytophthora parasitica as compared to the control (without broadcasting and drenching) and the chemical treatment which granule formulation of metalaxyl (Ridomil 5 G, at 40 g/square m). Determination of plant health during the experimental period (24 mo.) indicated the reduction of plant health index (PI) by 20 percent in the control whereas the PI of all treatments with application of antagonistic microorganisms remained high. Suspension of antagonistic microorganisms was prepared by mixing 5,500 g powder of T. harzianum (CB-Pin-01) or B. subtilis (B-03) with 400 l of water and supplemented with 400 ml Maltanic sugar or molasses and sticker. Spraying of antagonist suspension over the soil surface under tangerine canopy 4 times during 23 mo. of experiment, help increased populations of T. harzianum and B. subtilis in soil, while the populations of P. parasitica were reduced relative to the control. Plant health index of tangerine trees in the control was reduced, whereas the PIs of spraying treatments remained high. The benomyl resistant mutant isolate M23 of T. harzianum was used as a tool for determining the population dynamic of T. harzianum in soil after applying into potting soil and orchard soil. Results supported the evidences and roles of T. harzianum in reducing populations of P. parasitica and obviously proved the surviving ability of increased T. harzianum in soil. The efficacy of T. harzianum (M23) to reduce P. parasitica populations was comparable to T. harzianum (CB-Pin-01). Studies on the effect of 0.1 percent molasses on population dynamic of antagonistic microorganisms and P. parasitica in potting soil and orchard soil revealed the increase of efficacy of antagonistic microorganisms to reduce P. parasitica populations and to supported the increment of T. harzianum population.