STUDY ON THE INFECTION STATUS OF SCLEROTINIA STEM ROT OF RAPESEED IN DIFFERENT REGIONS OF MAZANDARAN PROVINCE *

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is one of the rapeseed important diseases in the world and Iran. In order to study the infection status of this disease in rapeseed fields of Mazandaran province, 120 fields in five different regions of Mazandaran (including Sari, Babolsar, Dashte Naz, Behshahr and Galogah) selected during years 2010 and 2011. From the beginning of disease symptoms appearance, weekly surveys were done from fields and amount of disease was recorded during the infection period. Based on the highest disease incidence on leaves, there were no significant differences between regions and fields in first year, but in second and combined two years, there were significant differences (P<0.001) between regions and years. The infection in first year (35%) was higher than second year (24%) and the region Galogah had the highest infection (42%) and Sari lowest infection (20.8%). Based on the final disease incidence on stems, there were significant differences between regions (P <0.001), but no significant differences between years. Based on disease severity, there were significant differences between regions (P <0.001) and years (P <0.05). Disease incidence was 21% in both two years and disease severity in first year (15%) was more than second year (11.5%). In combined two years, Galogah with disease incidence 32% and severity 21.2% had the highest infection and Sari with disease incidence 13.75% and severity 8.25 % had the lowest infection. Based on areas under disease progress curves, there were significant differences between regions and years, that these factors in first year were more than second year and in regions Galogah and Behshar were more than other regions.