F. Taliei - Department of Plant Pathology, College of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
N. Safaie - Department of Plant Pathology, College of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
M. A. Aghajani - Department of Plant Pathology, Agriculture and Natural Resources Research Center of Golestan, Gorgan, Islamic Republic of Iran.

Charcoal rot caused by Macrophomina phaseolina is an important disease of soybean throughout the world. To understand the spatial distribution of soybean charcoal rot incidence and M. phaseolina populations in Golestan Province, ۱۷۲ soybean fields were surveyed for population density, in two successive years, and integrated with Geographic Information System (GIS). Each year, ۶۰ fields were also surveyed for disease incidence. Propagule density was determined by assaying five ۱-g subsamples of soil from each field using a size-selective sieving procedure. In the seasons of ۲۰۰۹-۲۰۱۰ and ۲۰۱۰-۲۰۱۱, disease incidence ranged from ۰ to ۹۷% and ۳ to ۹۱% with the highest in Gorgan and Aliabad, respectively. Total mean of disease incidence were ۲۱.۰۱ and ۳۵.۸۴ percent in the province. In the two sampling years, Sclerotia were recovered from ۷۳.۳۳ and ۹۳.۵۷% of the total fields. The average population density per gram of soil ranged from ۰.۶۵ to ۱۴.۳۱ and ۴.۷ to ۱۶.۹, respectively, with the highest levels in Aliabad in both years. Charcoal rot incidence was positively correlated with soil populations of M. phaseolina (r= ۰.۶۱ and r= ۰.۴۷, P= ۰.۰۱). Geostatistical analyses of the survey data showed that the influence range of propagule density and disease incidence was between ۸,۰۰۰ to ۱۴,۰۰۰ m. In general, no significant correlation could be found between soil factors and sclerotia numbers. But, higher average air temperatures and decreased precipitation may have a significant effect on disease intensity.

geostatistics, GIS, Golestan Province, Iran, Plant disease