Naro to release cassava hybrid varieties

Cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) are two viral diseases that cause severe yield losses in cassava of up to 100 percent, thereby persistently threatening food and income security in sub-Saharan Africa.

For effective management of these diseases, there is a critical need to develop and deploy varieties with dual resistance to CBSD and CMD which researchers have been doing over time to come up with a number of varieties.

Background

Cassava brown streak disease and cassava mosaic disease have persisted as major constraints to the production of cassava in sub-Saharan Africa where the crop serves as a major staple food.

As such scientists at the National Crops Resources Research Institute (NaCRRI) in Namulonge believe the new cassava variety being bred will be disease-resistant. 

However, since the cassava vigour keeps reducing leading to disease infection, they have been breeding a set of cultivars from locally grown varieties which is under selection for the best variety.

Process of breeding

When Seeds of Gold arrives at Namulonge, the head of Root Crops Programme at the Institute, Dr Chris Omongo and a group of scientists are busy harvesting the trial cassava for laboratory tests.

Dr Omongo says the new varieties include the Nase series namely Nase 14, 18 and 19.

Climate change

Dr William Esuma, who is part of the breeding team says scientists are dealing with aspect of climate change, agro industrialisation and seed system in a bid for farmers to access clean cassava cuttings.

He says the research process is using conventional technology. 

There were more than 200 clones in the initial breeding process and the team has been planting these clones at Namulonge, the National Semi Arid Resources Research Institute (NaSARRI), Ngetta Zonal Agricultural Research and Development Institute (Ngetta ZARDI) and Abi Zonal Agricultural Research and Development Institute (Abi Zardi) in Arua.

This is for purposes of testing the vigour of the cultivars in the various agro ecological zones because once the variety selection is concluded, it must be able to grow in all these zonal areas.

Breeding

Dr Robert Kawuki, senior principal research officer at the institute notes that the harvesting exercise is aimed at developing cassava cultivars which are competitive and able to be taken up by farmers who are already growing existing varieties.

“We began this research work by going on ground to identify farmer needs. Some farmers demanded good yield rates while others were interested in its nutrition value. It is the reason we have cassava roots which are yellow and others are white,” he notes.

“The team during harvesting are carrying out different roles, others are collecting cassava roots to test the cyanide, others are weighing a heap from one root to get the yield rate, some are evaluating pest and disease effects while others are evaluating the test both as flour and boiled,” says Dr Kawuki.

One scientist collected seven cassava tubers which weighed 17.8 kilogrammes meaning it has good vigour in as far as the yield rate is concerned.

Out of the 200 clones the team planted, 43 have so far been selected.

They are now in the process of further selection to come up with one or two clones that suit the desired attributes for farmer use.

“The team wants a cassava variety which is resilient to pests and CBSV, free from cyanide and not bitter, its output is as far as flour is concerned must be good as well as quality,” says Dr Kawuki.

Tests conducted

Dr Ephraim Nuwamanya, a research Biochemistry at NaCRRI explaining the testing aspect for further evaluation says once cassava is grown in the trial fields and it is going to be released to farmers, it must be palatable.

“At the laboratory we test if the cassava is bitter or sweet and when you mingle it, is it sweet? This we do by evaluating the carbohydrates against its fibre. We use a system called penetrator to test its softness and hardiness. This will enable us to tell the breeder that the variety is either hard or soft, it has very low carbohydrates and low fibre,” he says. If the cassava under trial is high yielding as long as it is not cleared by the chemist, then it is not advisable for release to the farmer.

When all this evaluation process is concluded then, the researchers will begin the release process by following he required proceed.

Key fact

 Pests and diseases are the biggest constraints to cassava production in Uganda. Statistics indicate that they can cause losses of up to $24.2m (Shs81.7b) annually. When harvested and fresh from the ground, the new cassava varieties can yield 14 to 55 tonnes per hectare as long as the farmer follows the right agronomy practices.