ANASTOMOSIS GROUP AND PATHOGENICITY OF ISOLATES OF RHIZOCTONIASOLANI FROM POTATO CROPS IN SOUTH AUSTRALIA

Isolates of Rhizoctonia collected from the stems, roots, tuber sclerot ia and soil of potato crops in Virginia and Lenswood, South Australia, were identified to anastomosis groups (AG). Of the 301 multinucleate isolates of Rhizoctonia solani tested, 90% were AG-3. 7% were AG-4 and 2% were AG-5; 12 isolates were binucleate Rhizoctonia spp. This is th e first report of isolates of AG-4 and AG-5 causing disease in potato crops in South Australia. All AG-3, AG-4 and AG-5 isolates tested caus ed rhizoctonia disease symptoms on the potato cultivar Coliban in path ogenicity trials conducted under glasshouse conditions. Both AG-3 and AG-5 isolates caused black scurf and stem cankers, although symptoms o f black scurf were less severe with AG-5. AG-4 isolates produced the m ost severe stem and stolen cankers of all isolates tested. The pathoge nicity of tuber-borne inoculum was confirmed by growing plants from sc lerotia-infested tubers. AG-8 isolates from diseased barley and wheat produced severe root cankers and caused loss of feeder roots on inocul ated potato giants. Results suggest that rhizoctonia disease in potato fields in South Australia is caused by a combination of different ana stomosis groups and this has important implications for crop rotations .