Effect of Temperatures and Culture Media on Sclerotium rolfsii Mycelial Growth, Sclerotial Formation and Germination

Abstract

Sclerotium rolfsii is a serious soilborne phytopathogenic fungus causing serious yield loss in crops of high economic importance. In this study, the effects of temperatures and culture media were evaluated on S. rolfsii mycelial growth, sclerotial production and germination. The three isolates tested grew over a range of temperatures from 10°C to 35°C but not at 5°C and 40°C. Radial growth and dry mycelium production were highest at 30°C. Sclerotial initiation started on the 3rd day after incubation at 30°C and 35°C, and mature sclerotia were observed after 15 and 6 days of incubation, respectively. Optimal sclerotial production and the dry weight of 100 sclerotia varied depending on isolates and temperatures and occurred at 25°C-35°C. No mature sclerotia were produced at 5°C, 10°C, 15°C and 40°C. Sclerotial germination, noted after 24 h of incubation, was 96%-100% at 25°C-35°C, declined at 15°C-20°C, and was totally inhibited at 5°C, 10°C and 40°C even after 72 h of incubation. For all S. rolfsii isolates, optimal radial growth occurred on OAT medium followed by CZA, MYEA and PDA. When grown on PDA and OAT media, S. rolfsii developed cottony colonies with abundant mycelium whereas on WA and CZA pathogen growth was thin and scanty. Colonies formed on the other media developed sparse and flat mycelia. For sclerotial formation, WA and CZA were the most suitable culture media but no dark brown sclerotia were observed on NA and YDA. The highest sclerotial formation was observed on PDA and CZA. The highest sclerotium weight was produced by Sr3 isolate on PDA whereas for Sr1 and Sr2 isolates, sclerotial weights were significantly comparable on PDA, MYEA and CZA. Sclerotial germination was optimal on all tested media except NA. The significance of these findings on S. rolfsii biology is discussed.