1 February 2024
Although neighbouring countries have suspended the import of potatoes and seed potatoes from South Africa to prevent the spread of a new virus, experts believe its impact will not be too severe.
Pepper ringspot virus (PepRSV), which is rapidly taking hold in potato production areas in South Africa, was officially reported in the country in 2022.
Until December, it was classified as a quarantine disease, affecting the marketing of potatoes, says Dirk Uys, manager of research and innovation at Potatoes SA.
Table potatoes can now be marketed again because the infection is often symptom-free and its impact is relatively low.
“However, the situation affects seed potato growers because nuts that test positive for the virus cannot be marketed, in an attempt to limit its spread,” says Uys.
“I don’t think the virus will harm the supply of potatoes or nuts. It is a very small percentage of South Africa that is infected, so I believe we will have enough potatoes.”
Plant material can be tested by the laboratories of the Agricultural Research Council (ARC) or Patho Solutions (PathSol). Independent certification services will also be on the lookout for symptoms of the virus.
Neighbours close their borders
According to Uys, the impact of the virus on yields is not yet known. “At this stage, it seems that table producers are not suffering major losses, but it is important to eliminate viruses to optimise production. I must also emphasise that infected potatoes are still suitable for use.”
As a precautionary measure, South Africa’s neighbours have closed their borders to potatoes from South Africa while seeking more information. At least 6%-7% of South African potato production is exported.
“Discussions are currently under way because it is important for consumers to have access to potatoes, which are an affordable source of nutrients,” says Uys.
Symptoms and spread
Symptoms of PepRSV include ring-shaped spots on tubers and ring-shaped internal browning. On the leaves, the virus is observed as yellowing. It often occurs as a latent infection and can easily be confused with internal browning.
According to Uys, the virus was first reported in Brazil in the 1960s.
<caption>The yellowing of the ring spot virus on the plants’ leaves. Photo: Supplied
“The virus has a wide range of hosts, such as ground cherry, wild tobacco, wild dogwood, wild tobacco, beans, peas, tomatoes, chillies, fava beans, sunflowers and artichokes. It is often symptomless, making it easily overlooked. However, it can spread mechanically through plant material such as seed potatoes. The ARC is currently investigating the role of the stubby-root nematode in the spread of the virus.”
Dr Lindy Esterhuizen of the ARC has already observed the virus in Limpopo, the Free State, KwaZulu-Natal, North West and the Northern Cape. It has also been identified in samples at fresh produce markets.
Combatting
According to Uys, PepRSV cannot be controlled with traditional crop protection products. Instead, the vectors that spread the virus must be targeted.
From the literature, it appears the stubby-root nematode is a possible vector, so it makes sense to test the soil for the presence of nematodes from the Trichodoridae group.
“The most important thing is to ensure that seed potatoes are clean, so we recommend that producers plant certified nuts. This is a preventative measure to combat the spread,” says Uys.
“Also, plant different cultivars from different sources to reduce the risk. Build a relationship with your supplier to confirm the quality of the nuts.”
The state manages PepRSV as a regulated disease, meaning it must be reported to monitor its spread. The virus was also reported a few months ago in sunflowers.
The Department of Agriculture, Land Reform and Rural Development did not respond to inquiries in this regard.
