Evaluation of Relative Resistance in Eleven Apple Rootstocks to Crown Rot Caused by Phytophthora cactorum

An experiment was conducted to evaluate relative resistance to P. cactorum, the casual agent of apple crown rot, in eleven apple rootstocks. The experiment was in factorial (with apple rootstocks and year factors) on the basis of completely randomized design with three replications. Each plot consisted of four young plants. All rootstocks excluding Morabbaei, were propagated vegetatively. One year old rootstocks were evaluated in pots containing soil inoculated artificially with inoculum of P. cactorum. Disease response of the rootstocks was assessed three months after inoculation based on canker length (cm), crown girdling (%), mortality (%) and mean canker area (cm2). The analysis of variance on pooled data showed that effect of rootstock on measured characterestics was significant at 1% probability level. MM106 rootstock was highly susceptible (mean canker area: 4.72 cm2, crown girdling: 89.33%, canker length: 5.28cm and mortality (%): 83.33%). M9, Azayesh and CK1 rootstocks were resistant and Morabbaei and MM111 rootstocks were moderately susceptible compared to the highly susceptible rootstock.. Gami almasi and CK2 rootstocks were moderately resistant and M26, M27 and B9 rootstocks showed relatively tolerance responces to P. cactorum. Interaction between year and rootstock was not significant.