Invasive whitefly threatens Africa's cassava crops

Whiteflies can cause extensive damage to crops

Flickr/USDAgov

[ARUSHA, TANZANIA] A species of whitefly that transmits cassava mosaic virus has been spotted in South Africa for the first time, and could hamper efforts to tackle the disease, a conference has heard.

Researchers from the University of the Witwatersrand, South Africa, conducted greenhouse and field studies between 2004 and 2010 for the common bean, cassava, sweet potato and tomato in eight South African provinces.

An invasive, non-indigenous silverleaf whitefly (Bemisia tabaci) was spotted several times during the study and was found to be particularly adept at spreading cassava mosaic virus.

Because of its ability to feed on different plants, the researchers say, the silverleaf whitefly poses a serious threat to many crops.

The researchers presented their findings at the 12th International Symposium on Plant Virus Epidemiology, in Arusha, Tanzania — organised and hosted by the International Plant Virus Epidemiology Committee and the International Institute of Tropical Agriculture (IITA) — last month (28 January–1 February). Their work is published in the February issue of the Journal of Applied Entomology.

"There are many other types of whitefly on plants in Africa," Chrissie Rey, a professor at the University of the Witwatersrand and one of the study authors, tells SciDev.Net. "If you have high populations of any whitefly feeding on a crop they can cause extensive damage just by feeding, irrespective of virus transmission."

The researchers say that the fly may have entered South Africa via trade in ornamental plant species — plants grown for decorative purposes — from the Middle East and the Mediterranean. Rey said at the conference that they are worried that the insect "could be spreading to other parts of Africa as it was recently reported from Mozambique on tomatoes".

The researchers are now calling for further study to ascertain the fly's entry into the country and "to sample more crops and know how widespread the disease is", said Rey.

The forum also heard that Africa urgently needs to shift to the cultivation of hardy crops such as cassava and millet to deal with the negative consequences of climate change.

Elsewhere at the conference, Nteranya Sanginga, director-general of the IITA, told SciDev.Net that cassava's drought-tolerant qualities make it the food crop that could potentially save Sub-Saharan Africa from food insecurity.

Sanginga said Africa countries should put in place appropriate policies to accompany this diversification. For instance, only Nigeria has a national policy on cassava, allowing the country to replace 20 per cent of wheat flour — mostly imported — saving the country about US$20 million per year.

"Other countries including the Democratic Republic of Congo, Ghana and Malawi have their policies in parliament for discussion," Sanginga said.

Link to full paper in Journal of Applied Entomology

This article has been produced by SciDev.Net's Sub-Saharan Africa desk.