The reaction of some apple rootstocks to biocontrol of white root rot Rosellinia necatrix by Trichoderma harzianum in greenhouse

Three Trichoderma harzianum isolates, were evaluated for their antagonistic effect on Rosellinia necatrix causal agent of white root rot (WRT). According to in vitro evaluations, T. harzianum T20A isolate showed the most pathogen growth inhibition. The inoculum of T20A isolate was applied to control WRT disease on four commercial apple rootstocks: Malling (M7, M25) and Malling Merton (MM111, MM106) in greenhouse experiments. Root rot and leaf fall indices were measured 70 days after pathogen inoculation. The biocontrol agent had a significant effect (p < 0.01) on the reduction of pathogen indices but the effect of rootstocks was not significant. Root rot reduction on MM111, MM106, M25 and M7 rootstocks were 63.84%, 61.13%, 28.63% and 17.47%, respectively. The antagonist also caused reduction of leaf drop symptom on MM106, M7, MM111 and M25 infected apple rootstocks by 57.4%, 56.06%, 44.09% and 40.24%, respectively. Disease indices were also measured for fungicide treatment and the results were compared with disease indices in antagonist treatments. The most biological control was observed on MM111 (63.84%) and MM106 (57.4%) according to the reduction in root rot and leaf drop, respectively. The reactions of apple rootstocks to WRT were also evaluated. The results showed that all the rootstocks were susceptible to WRT in the greenhouse condition. The MM106 rootstock which showed 100% root rot and 78% leaf drop was the most susceptible and M7with 43.5% root rot and 84.56 leaf drop was the least susceptible in our experiment. This was the first study of reaction and biocontrol of white root rot disease on apple commercial rootstocks in Iran and the results suggest a better insight to disease management either by integrating resistance and biocontrol measures or replacing chemical control by antagonist application to soil.