Effect of temperature on mycelial growth and microsclerotial germination of causal agent fungus of soybean charcoal rot

Macrophomina phaseolina is a soil born fungal pathogen that caused charcoal rot of soybean and several other plants. Disease intensity in different hosts is related to hot and dry weather condition. In order to determination of cardinal (minimum, optimum and maximum) temperatures required for mycelial growth and microsclerotial germination, three fungal isolates prepared from soybean fields of three regions Aliabad, Gorgan and Kalaleh in Golestan province were studied in vitro. Mycelial growth and germinated microsclerotia number were recorded daily in different temperatures and fitness of data with three growth models (Beta, segmented and dent-like) were examined. Results of statistical analyses (nonlinear regression) showed that the segmented was the most suitable model for describing the relationships between mycelial growth and microsclerotial germination of this fungus. Minimum, optimum and maximum temperatures estimated by the segmented model for mycelial growth were 8, 34.5 and 44.3 ºC, respectively, and 8.9, 32.3 and 45.5 ºC for microsclerotial germination.