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 T۲۰A isolate showed the most pathogen growth inhibition. The inoculum of T۲۰A isolate was applied to control WRT disease on four commercial apple rootstocks: Malling (M۷, M۲۵) and Malling Merton (MM۱۱۱, MM۱۰۶) in greenhouse experiments. Root rot and leaf fall indices were measured ۷۰ days after pathogen inoculation. The biocontrol agent had a significant effect (p < ۰.۰۱) on the reduction of pathogen indices but the effect of rootstocks was not significant. Root rot reduction on MM۱۱۱, MM۱۰۶, M۲۵ and M۷ rootstocks were ۶۳.۸۴%, ۶۱.۱۳%, ۲۸.۶۳% and ۱۷.۴۷%, respectively. The antagonist also caused reduction of leaf drop symptom on MM۱۰۶, M۷, MM۱۱۱ and M۲۵ infected apple rootstocks by ۵۷.۴%, ۵۶.۰۶%, ۴۴.۰۹% and ۴۰.۲۴%, 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 MM۱۱۱ (۶۳.۸۴%) and MM۱۰۶ (۵۷.۴%) 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 MM۱۰۶ rootstock which showed ۱۰۰% root rot and ۷۸% leaf drop was the most susceptible and M۷with ۴۳.۵% root rot and ۸۴.۵۶ 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.

Keywords:

Malus domestica , Trichoderma harzianum , apple rootstock , Rosellinia necatrix , white root rot , biological control