Determination of the anastomosis grouping and virulence of Rhizoctonia spp. associated with potato tubers grown in Lincoln, New Zealand.

A total of 58 isolates of Rhizoctonia spp. (46 R. solani and 12 binucleate Rhizoctonia) were recovered from potato tubers showing black scurf disease symptom during the 2004 growing season in Lincoln, New Zealand. The isolates were assigned to 5 Anastomosis Groups (AG) ofR. solani AG-3 (54.34%), AG-5 (28.26%), AG-8 (8.69%), AG-4 (6.52%) and AG-2-2 IIIB (2.17%) and six anastomosis groups ofbinucleate Rhizoctonia, AG-K (25%), AG-Bi (25%), AG-Ba (8.33%), AG-C (8.33%), AG-D (8.33%) and AG-E (8.33%). Two isolates of BNR did not anastomose with any of the tester strains and remain unidentified. In pathogenicity tests that were carried out on radish, carrot, lettuce, onion, tomato and hemp, it was found that all the isolates of both R. solani and binucleate Rhizoctonia to be virulent at varying degrees to these 6 plants species from different families. In these tests, isolates of AG-3 and AG-8 from R. solani population caused the highest and lowest disease severity on all 6 plant species, respectively. In population of binucleate Rhizoctonia, on the other hand, the highest and lowest disease severities were caused by the isolates of AG-D and AG-Ba on all test plants, respectively. When the results of the pathogenicity tests were examined in terms of the susceptibility levels of the plants, the most resistant plant was tomato against different AGs of R. solani and BNR. On the other hand, radish was the most susceptible plant species tested in this study against both R. solani and BNR isolates.