Effects of nutrient status, temperature and pH on mycelial growth, sclerotial production and germination of Rhizoctonia solani from potato.

SUMMARY The effects of nutrient status, temperature and pH on mycelial growth, sclerotial production and germination of Rhizoctonia solani [anastomosis groups (AGs) 21 and 3] from potato were studied on a range of artificial media including potato dextrose (PDA), malt yeast extract (MYA), water (WA) and soil extract (SEA) agar. Greatest sclerotium yields were obtained on MYA for AG 3 and PDA for AG 2-1. Sclerotium yields were significantly poorer for AG 2-1 isolates compared to AG 3 isolates tested. Sclerotium yields were significantly improved when mycelia grown on nutrient poor (WA) agar were transferred to nutrient rich (PDA) media after 4 d for AG 3 isolates, but not for AG 2-1 isolates. Optimum temperatures for mycelial growth of all isolates were between 20 and 25°C on all media tested. Mycelial growth of all isolates occurred between pH 4 and 9, with an optimum of pH 5.6. Sclerotium formation occurred between pH 4 and 8 and pH 5 and 6 for AG 3 and AG 2-1 isolates, respectively. Sclerotial germination for all AG 3 isolates was optimal between 20 and 30°C on all media tested, with a pH optimum between pH 5 and 6. In soil, AG 2-1 isolates grew significantly slower compared to AG-3. Optimum temperature for mycelial growth in soil was between 20 and 25°C, regardless of anastomosis group. Sclerotial germination in soil by AG 3 isolates occurred between 10°C and 30°C. The significance of these results on the pathogenicity of R. solani is discussed.