Survival of Macrophomina phaseolina and Associated Mycobiota on Soybean Residuals and the Effect of Trichoderma harzianum on Their Population Dynamics

Macrophomina phaseolina, the causal agent of soybean charcoal rot is an important pathogen in soybean growing regions of the world, including Iran. Survival of M. phaseolina and associated mycobiota on soybean residual was studied every two months over a eight-month period, for two years, under environmental conditions of Golestan province, Iran. In the first year, root segments colonized by M. phaseolina were placed into polypropylene-mesh bags and buried in depths of 0-5, 10-15, and 20-25 cm at M. phaseolina infected and uninfected soil in the field microplots. The percentage of isolation frequencies for M. phaseolina showed a slow decrease linear trend over time, from 93.3% before burial to 73.6 %, eight months later. Trichoderma spp. were isolated at positive slow linear trend and was increased 6% over time. Isolation frequencies of M. phaseolina were similar among the three soil depths over all sampling dates at both soil types. In the second year, mesh bags, included M. phaseolina colonized residual, were buried in the field microplots at infected and sterile soil treated with Trichoderma harzianum MKR 1321 inoculum, in comparison to untreated one. Percentage of isolation frequencies for M. phaseolina decreased 77.5% over time in T. harzianum treated soil compared to 11.2% in untreated soil regardless of soil type. Isolation frequencies of Trichoderma spp. was also increased 93.9% in treated soil. The increase of Trichoderma spp. paralleled with the decreasing in isolation frequencies of M. phaseolina and other fungi. These findings suggest that the combined role of Trichoderma spp. as strong tissue degraders and mycoparasites may lead to reduce the survival of the pathogen M. phaseolina and other associated fungi in burial debris.