The Brassica Stunting Disorder, which has been dubbed “Pathogen X” in South Africa, has been confirmed as a virus, with the name of the virus due to be released by a dedicated research group in the near future.
A collaboration of industry partners has contributed towards the research in identifying this pathogen and investigating control methods in the future. The pathogen was first observed in Brits in 2012 and has spread throughout the country over the past two years, with the most recent infections reported in Southern KZN. Typical symptoms of this virus include stunting; purpling/yellowing of the leaves; flattening of the leaves; side shoots with no head formation and poor root formation. The identification of the pathogen is relatively easy if one cuts across the stem – one observes the blackening of the vascular tissue (phloem) forming a black ring in infected plants.
The pictures below clearly illustrate these symptoms. Research conducted by Miss Sherrie-Ann New of the University of Johannesburg has shown that the pathogen is biotic; is not seed borne; is not soil borne and that infection occurs in clusters, typically 4-6 weeks after transplanting. The insect vectors that spread this pathogen appear to be predominantly aphids; thrips and leafhoppers. More research to isolate the responsible vector is underway.
Viruses are difficult to control and the focus is typically on controlling the insect vectors and breeding resistant varieties. The best course of action for now as a grower of brassica crops is to implement a preventative spray program that controls the insects mentioned above. As and when more information becomes available, updates will be posted to this website.