THE OCCURRENCE AND PATHOGENICITY OF RHIZOCTONIA FUNGI IN SOUTH-AUSTRALIAN PLANT NURSERIES

Potting mixes and plants exhibiting symptoms of root disease were coll ected from 30 nurseries or potting mix suppliers in South Australia. T hirty-nine isolates of Rhizoctonia were obtained from 11 sampling loca tions by isolating from diseased plants, planting media, or by isolati ng from the roots of bait seedlings (zinnia, brussels sprouts, radish, bell pepper, wheat and ornamental lupin) grown in the planting media. Thirty-five isolates were binucleate and four were multinucleate. Bin ucleate isolates anastomosed with known groups AG-A, AG-I, AG-K or CAG 5 and 10 were not able to be placed in any known group. Multinucleate isolates belonged to AG-2-1 and AG-4. Certain AG-4 multinucleate isol ates reduced the growth of wheat or bell pepper while certain binuclea te isolates decreased the growth of wheat or increased the growth of b ell pepper. Although multinucleate Rhizoctonia fungi can cause severe disease of bedding plants, it is difficult to predict such damage due to the influence of potting mix edaphic factors and variability in pat hogenicity of the isolates present.