New Anastomosis Group F (AG-F) of binucleate Rhizoctonia causing root and stem rot of Pistacia vera

A total of ten isolates of fungi with Rhizoctonia-like mycelia were obtained from infected roots and stems of Pistachio Pistacia vera grown in a commercial nursery in Rafsanjan, Iran, during the autumn of 2011. The infected seedlings showed symptoms of chlorosis that later turned to necrosis. All of the isolates were identified as binucleate Rhizoctonia on the basis of hyphal characteristics and nuclear number. They were tested for detection of the anastomosis group, optimum growth temperature, rDNA-ITS region traits and pathogenicity on pistachio seedlings in vitro and in vivo. The analysis of hyphal anastomosis reaction was carried out with the tester isolates of binucleate Rhizoctonia AG-A, AG-Ba, AG-G and AG-F as well as multinucleate Rhizoctonia AG4 as already detected on pistachio seedlings. The optimum temperature for growth of binucleate Rhizoctonia sp.was 35 °C. In in vivo test, the symptoms of root rot were observed 30 days after inoculation and mortality happened two weeks thereafter. According to molecular characteristics and anastomosis test groups, all isolates showed greatest similarity to anastomosis group AG-F. This finding is the first report of anastomosis group F (AG-F) of binucleate Rhizoctonia, as causal agent of root and stem rot disease of pistachio in the world and Iran.