New Anastomosis Group G (AG-G) of binucleate Rhizoctonia sp., the causal agent of root rot disease on miniature roses in Iran

Rhizoctonia-like fungi were isolated from the infected roots of miniature rose (Rosa hybrida cv. Linda) plant with chlorosis and necrosis symptoms, grown in commercial glasshouse in Rafsanjan, Iran, during the autumn of 2011. All of the isolates were identified as binucleate Rhizoctonia sp. on the basis of hyphal characteristics and nuclei number. They were tested for detection of the anastomosis group, optimum growth temperature, rDNA-ITS region traits and pathogenicity on miniature rose in vivo and in vitro. The analysis of hyphal reaction anastomosis was carried out with the tester isolates of binucleate Rhizoctonia AG-A, AG-Ba, AG-G as well as multinucleate Rhizoctonia AG2-2IIB and AG4-HGI already detected on miniature rose. The optimum temperature for growth of binucleate Rhizoctonia sp. was 35°C. In in vivo test, the symptoms of root rot were observed 35 days after inoculation and mortality happened two weeks later. According to molecular and anastomosis test groups, our results showed that all the isolates have the maximum similarity to AG-G. This is the first report of anastomosis group G (AG-G) of binucleate Rhizoctonia sp., thecausal agent of root rot disease on miniature roses in Iran.