Prevalence of Sclerotinia sclerotiorum sclerotia recovered from soybean and sunflower silo's

The fungal pathogen, Sclerotinia sclerotiorum, causes significant disease in oil-seed crops, and produces sclerotia, primarily serving as a survival structure, but also as means of dispersal. The aim of this study was to quantify sclerotia recovered from South African soybean and sunflower silos between 2012/2013 and 2020, for each crop respectively. Historic data were retrieved from a public database managed by the South African Grain Laboratories. A one-way analysis of variance (ANOVA) and summary statistics were visualized to determine variation in percentage (mass per seed mass) and prevalence (percentage of positive seed lots) of sclerotia recovered. Sclerotia recoveries were mapped to determine regions and years which were below or above legislative and industry sclerotia thresholds. A total of 190 and 163 soybean and sunflower silos were sampled, respectively, where between 100 and 176 3-kg sub-samples per annum were included. Prevalence of sclerotia recovered ranged between 33.3% (2015) and 78.3% (2020) in soybean production regions and 9.1% (2013) and 95.0% (2020) in sunflower production regions. ANOVA indicated significant differences between reported years, for both crops, and variation in frequency of sclerotia with regard to policy thresholds. Sclerotia recovered may provide an indication of sclerotia retained in farm-saved seed as well as sclerotia remaining on and in fields. South Africa is one of the few countries with national and industry policies in place to monitor and restrict sclerotia in seed. This practice should continue, with the addition of research, which is underway, to understand the risk associated with S. sclerotiorum to remain seed-borne and potentially cause infections.

Automated summary

The aim of this study was to quantify the recovery of Sclerotinia sclerotiorum sclerotia from South African soybean and sunflower silos between 2012/2013 and 2020. The prevalence of recovered sclerotia ranged from 33.3% to 78.3% in soybean production regions and from 9.1% to 95.0% in sunflower production regions. There were significant differences between years for both crops, and variations in the frequency of sclerotia with regard to policy thresholds.