Cassava disease control underway

DISEASE resistance trials for cassava being conducted simultaneously in 33 different locations across five African countries and involving 25 shared varieties are showing promise against the deadly Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD).

According to a statement, this first-of-its-kind multi-country collaborative cassava breeding initiative in East and Southern Africa is part of a major activity of the new cassava varieties and clean seed to combat CBSD and CMD (5CP) project which is funded by the Bill & Melinda Gates Foundation.

The project is led by International Institute of Tropical Agriculture (IITA) working in collaboration with the national agricultural research systems of Kenya, Malawi, Mozambique, Tanzania and Zambia where the trials are being conducted. 

The project is in its final year of implementation.

Dr Edward Kanju, IITA cassava breeder and coordinator of the 5CP project, said that preliminary results of the trials have already shown that several of the new varieties are virtually unaffected by CBSD and CMD, even in locations where disease pressure is extremely high from infected fields surrounding the trials. "Although in many of the countries the varieties are undergoing their first year of trials, our initial results are already showing good promise.

We will further validate the performance of these varieties by comparing them to local ones that have been selected as checks," he explained. This landmark regional initiative is aimed at speeding-up the breeding of cassava varieties with dual resistance to CMD and CBSD in the five countries where the diseases are of great concern. Each of the countries selected five of its best varieties in terms of performance against CMD and CBSD and shared them for the inter-country trials.

The planting materials first underwent a rigorous clean-up exercise to ensure they are virus-free before being distributed as tissue culture plantlets. This is the first time that breeders in the five countries have freely shared their best varieties in a concerted effort to tackle the two deadly diseases.

Dr James Legg, IITA virologist, highlighted another objective of the 5CP Project, which is the establishment of pilot clean seed distribution system in Tanzania, which he is leading. "We are perfecting the cassava seed systems in Tanzania through a three-step approach: Virus indexing, then rapid multiplication at a research station and finally large-scale multiplication at a clean site in an area with low disease pressure."

Dr Legg said that they have established clean seed sites in Mtwopa (Mtwara), Mwele (Tanga), Hombolo (Dodoma) and Nkenge (Kagera) in Tanzania's cassava-growing heartland. He added that they are routinely monitored and carefully managed and that he was happy to report that there have been very low incidences of CMD and CBSD in these sites.

"Moreover, the sites are now being used by the Tanzania Root and Tuber Research Programme to produce quality planting material of new, popular and disease-resistant varieties such as Mkuranga 1, Chereko, Kipusa and Kizimbani, as well as some of the older favourites, such as Mkombozi, Kiroba and Mumba," added Dr Legg.

The virus cleaning was carried out by the Natural Resources Institute (NRI) and the Kenya Plant Health Inspectorate (KEPHIS).

The material was forwarded to Genetics Technologies International Limited (GTIL), a commercial tissue culture company, for mass multiplication. The plantlets were then certified virus-free by the Mikocheni Agricultural Research Institute (MARI) and IITA.

Another major development of the project is the establishment of rapid multiplication systems for mini-plants derived from virus-indexed tissue culture plantlets.

By using these rapid propagation techniques in screen houses, the team led by Dr Kiddo Mtunda, cassava researcher and Officer-in-Charge of the Sugarcane Research Institute (SRI) in Kibaha, Tanzania and her team have been able to produce thousands of cassava plants in a matter of months. T

he success of this project offers promise not just for cassava producers in the target countries, but more widely to cassava producers throughout Africa.