Rosette virus disease and its threat on smallholder productivity

By GLORIA SIWISHA, Chipata

AN epidemic of groundnut rosette disease threatens to drastically reduce the 2019/2020 groundnut yield in the Eastern Province of Zambia.

Preliminary data obtained from the Zambia Agriculture Research Institute ZARI’s Msekera research station in Chipata, shows that the most severely affected smallholder groundnut fields are those in Chipata, Kasenengwa, Chipangali, Katete, and Petauke districts.

As an off-shoot of weather related risks like late on-set of rains, droughts and dry-spells, groundnut rosette disease is said to be the most devastating virus disease of groundnuts in Sub-Saharan Africa with the potential to cripple rural economies.

Research has shown that rosette virus disease can reduce groundnut yields by 70 to 90 percent.

According to Yayock et al. 1976, an epidemic in northern Nigeria in 1975 destroyed approximately 0.7 million hectares of groundnuts, with an estimated loss of US$ 250 million.

Similarly, an epidemic in eastern Zambia in 1995 affected approximately 43,000 hectares causing an estimated loss of US$4.89 million (ZARI, Msekera, 1995 Reconnaissance Survey report).

In the following year, in the central region of Malawi, groundnut production was reduced by 23 percent with an estimated economic loss of US$9 million, according to the 1996 SADC/ICRISAT groundnut project.

As per estimate of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), groundnut rosette disease causes an annual loss of US$ 156 million in Sub-Saharan Africa.

Experts assert that groundnut rosette disease (GRD), is a virus disease that is transmitted by the groundnut aphid (Aphis craccivora).

It has been observed that population dynamics of the groundnut aphid is triggered by late or uncertain onset of planting rains.

The resultant dry spells during the planting period create favorable conditions for increased aphid populations.

These increased populations of aphid in turn transmit the rosette virus to the young and tender groundnut plants.

The main symptoms of groundnut rosette disease, according to Msekera research station Principal scientist and station manager Kennedy Kanenga, are stunting and distortion of groundnut plants with reduced leaf size, resulting in bushy appearance of plants.

There is also a yellowing or mottling of the foliage.

If not managed, rosette virus disease it is argued, causes severe damage to crops.

Plants that are infected early, will produce no yield.

Robert Phiri, 56, is a smallholder producer of Chinjala resettlement area in Kasenengwa district.

He laments the loss of 3 tonnes of yield from his 0.8 hectares groundnut field due to the rosette virus epidemic this season.

“All things being equal, I would get close to 3 tonnes of groundnuts on a one hectare field but I doubt I will get three by 50 Kilogramme bags this year,” Mr Phiri said during a combined tour of his farm by seed Inspectors and research scientists from Msekera research station.

Phiri is one of the 67,000 groundnut farmers affected in the Eastern Province of Zambia.

On the other hand, farmers like Faides Chisanga of Chisitu agricultural camp in Chipata district who planted one of the 7 improved and resistant groundnut varieties this season, have managed to escape rosette disease infestations in their field.

Chisanga, an ardent producer of groundnut seed, is expecting a four times more yield of between 3 and 3.5 tonnes of groundnuts from her one hectare field. The national average yield being of 0.7 tonnes per hectare (t/ha) and the world average at 0.9t/ha.

The frequency of rosette outbreaks, scientists at Msekera research station reveal, have increased from every ten years in the past decade, to every three years recently owing to climate change.

Unfortunately, rosette virus disease, just like any other viral disease is not curable.

Non-the-less, there’s still hope for smallholder producers in the region and generally in Zambia.

So far, farmers are being advised to plant early and increase the planting population as spraying insecticides against aphids has neither been effective nor efficient.

Insecticides are also said to be costly for groundnut producers, the majority of whom are women, and thus increase the cost of producing groundnuts apart from being hazardous to human beings and the environment.

“Optimum planting time, usually as early as planting moisture can allow, and maintaining good plant density without any gaps, have shown to reduce rosette disease incidence to some extent.” Mr Kanenga said.

As an effort to further increase groundnut production and productivity, and strengthen, and sustain the groundnut supply chain in Eastern Province and the country as whole, the Msekera research team, in collaboration with its partners, has developed seven rosette resistant groundnut varieties.

They include Wamusanga, Wazhitatu, Lupande, MGV-6, MGV-7, MGV-8, and MGV-9.

These varieties have combined desired agronomic and consumer attributes. They are thus more productive, are tolerant to drought, have better taste and are easier to process into peanut butter.

Most importantly, smallholder farmers who cannot afford to buy and spray against vectors are saved from using expensive and hazardous pesticides.

According to Mr Kanenga, use of rosette resistant varieties also provides the most economical and practical solution to control groundnut rosette disease in the field.

“The strategy of managing the GRD epidemic at genetic level is the most promising and sustainable,” he said.

If put into the hands of smallholder farmers therefore, these technological innovations coming from research would enable them to not only increase groundnut production to strengthen the supply chain, but would also drastically reduce the cyclical negative impact of the groundnut rosette disease on trade.

Mr Kanenga says significant investment would be required to scale up rapid multiplication of these varieties both on station and through farmer out-grower schemes so that as many producers as possible, have access to improved seed.

He said so far, Zambia had attained a significant milestone in providing smallholder farmers with an option, -an innovative technology of new groundnut varieties that would enable the small-holder farmers’ increase and sustain their incomes despite the rosette virus disease epidemic.

“Limited access to improved seed is a perennial challenge for many farmers and it’s largely due to inadequate volumes of seed available. Msekera research station under ZARI, has a blue print to attempt to overcome the barrier. Through the Seed Unit, though, not fully fledged, we have been producing high quality legume seed of new varieties for seed companies and farmers. Significant investment is however required to scale up seed multiplication in order to improve access to rosette resistant seed,” he said.

Technological innovations such as the rosette resistant groundnut varieties developed by ZARI and partners, are no doubt tools that will transform and sustain the groundnut value chain in the country.

The smallholder groundnut producers will be guaranteed to economic benefits once they switch to using more adapted, rosette resistant and improved groundnut varieties to avoid losses in their investments as what has happened in the 2019/2020 agriculture season.