The occurrence and pathogenicity of Rhizoctonia fungi in South Australian plant nurseries

Abstract

Potting mixes and plants exhibiting symptoms of root disease were collected from 30 nurseries or potting mix suppliers in South Australia. Thirty-nine isolates of Rhizoctonia were obtained from 11 sampling locations by isolating from diseased plants, planting media, or by isolating 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. Binucleate 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 isolates reduced the growth of wheat or bell pepper while certain binucleate isolates decreased the growth of wheat or increased the growth of bell 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 pathogenicity of the isolates present.