impact of sclerotinia stem rot on canola yield in golestan province

sclerotinia stem rot (ssr), caused by sclerotinia sclerotiorum, is the most important diseases of canola (brassica napus) in iran. in order to study of the impact of ssr on canola yield, infection situation and yield of 80 fields in four different regions of golestan province (gorgan, ali abad, kalaleh and gonbad) in north of iran, was recorded during two growing seasons (2006 and 2007). ssr severity was estimated 0.6-66.8% and yield loss due to the disease was 0.3-34.7%. statistical relationship between ssr severity and field yield revealed that one percent increase in ssr severity, causes 0.52% yield loss, and this value corresponds to 0.25 and 0.4% ssr incidence in gonbad and other three regions, respectively. economical damage threshold of ssr in a canola field with potential yield of 2000 kg/ha. was calculated as 17.2 and 10.5% ssr incidence for gonbad and other three regions, respectively.