R4D Planning week: Halting spread of cassava rot disease in Africa

The Cassava Brown Streak Disease (CBSD) is one of the greatest threats to production of cassava which is an important source of food and income for millions of resource poor farmers in Sub-Saharan Africa.

IITA scientists working on various aspects of controlling the disease from breeding for varieties with resistance both conventionally and marker-assisted, to tracking the spread and disease vector, met to develop a strategy to intensify, in a coordinated way, their efforts to save the crop on the second day of the IIA planning week.

Dr James Legg, an IITA virologist told the group it was now irrefutably proven that the whitefly was the vector transmitting the cassava brown streak virus. However, he said, various studies were still underway to understand exactly how the transmission takes place.

Giving an update of conventional breeding efforts to develop varieties with resistant to the viral disease, Edward Kanju, IITA cassava breeder said there were over 30 promising genotypes for lowland areas in Tanzania at various stages. Some were under on-farm trials while otehrs showing great tolerance - they show leaf symptoms but no necrosis on the roots – were poised for official release very soon.

He said a breeding program started in 2004 in Uganda has developed three tolerant clones that have shown leaf symptoms but with no damages to the roots. They were the best options for the mid-altitude areas and there was a huge demand for them in the region.

Morag Ferguson, IITA molecular Biotechnologists, said a project started five years ago with the national program in Tanzania had identified suitable markers associated with the CBSD. She said though they had not been validated, which would take another three years, they could still be used to assit breeders especially as the situation was becoming more severe.

Since the CBSD was mostly spread by infected cutting materials, halting the movement of infected planting material should halt the disease spread. However, Lava Kumar, IITA virologist said this was not easy for CBSD as the symptoms on the leaves are not so clear.

He said this calls for extra caution when selecting planting material for multiplication to avoid spreading the disease further. Furthermore he said good diagnostic tools were available which needed to be used carefully and the testing carried out several times.

He added for countries where the disease was not present, there was a great need to create awareness on the disease, symptoms and control measures to arrest the situation in time.