Sclerotinia's Danger To Oilseed Production

In South Africa, Sclerotinia sclerotiorum is a particular threat to oilseed crops such as sunflower and soya bean. Annelie Coleman spoke to Dr Miekie Human, research and policy officer at Grain SA, and Dr Lisa Rothmann of the University of the Free State’s Department of Plant Sciences: Plant Pathology Division, about this fungal disease.

- Annelie Coleman

Sclerotinia sclerotiorum is a fungal plant pathogen that can cause diseases such as white mould, stem rot and head rot, resulting in significant yield losses in crops. Early disease symptoms include soft, watersoaked lesions that lead to the wilting of infected plants’ stems and branches. Dead tissue on the host plants looks as though it has been bleached. The white ‘fluffy’ mycelium, the vegetative part of a fungus, manifests either externally or internally.

The mycelium forms the survival structure of the fungus. Sclerotia are the hard, dark, resting bodies of fungi; they consist of a mass of hyphal threads and can remain dormant in the soil for long periods.

“S. sclerotiorum causes direct losses in terms of yield and indirect losses through reduced crop quality and diminished grade quality because of reduced seed size and seed germination, as well as substandard oil content,” explains Dr Miekie Human, research and policy officer at Grain SA.

WIDE RANGE OF CROPS AT RISK

According to Human, S. sclerotiorum is not host-specific, and over 500 plant species, including weeds, are susceptible to it. In South Africa, the most notable crops affected by the disease are soya bean, sunflower and canola. Cabbage, cauliflower, dry beans, tomatoes, peas and potatoes can also be targeted. Sclerotinia diseases occur across South Africa.