Abstract:
Alternaria leaf blight (ALB) has been shown in recent years to be one of the major potential disease threats of sunflower
capable of causing yield losses in all major production areas. The aim of this study was to determine the causal
agent, prevalence and geographical distribution of ALB in the major sunflower production areas of South Africa.
Surveys were conducted during 2012/13, 2013/14 and 2014/15 growing seasons at commercial sunflower production
fields and at commercial cultivar trials. In the three growing seasons, twenty-nine sunflower commercial production
sites were surveyed for ALB disease severity. Furthermore, four cultivars (AGSUN8251, PHB65A25, SY4200 and
PAN7049) were surveyed for ALB during cultivar trials in a total of 25 localities during the three growing seasons.
The plants were surveyed between 90 to 120 days after planting and leaves showing ALB symptoms were collected.
Alternaria alternata was identified as the primary disease-causing organism of ALB in all the fields. The site
Bothaville-Wesselsbron consistently had the lowest ALB disease severity during the 2013/14 and 2014/15 growing
seasons, whereas Potchefstroom had the highest disease severity in all three growing seasons. Pearson’s correlation
coe cient was greatest for temperature (r = 0:6 in 2012/13, r = 0:71 in 2013/14 and r = 0:84 in 2014/15) and disease
severity in all the growing seasons. Information about the distribution of sunflower diseases is important and this
survey demonstrated that A. alternata is widespread across sunflower production areas in South Africa and may result
in potential yield losses.