Crop science researchers at the National Crops Resources Research Institute (Nacrri) at Namulonge apart from improving cassava planting materials using the Biotechnology method in a bid to obtain resistant varieties against the cassava brown streak, have recently embarked on improving varieties that may not be infected by the white flies.
According to recent surveys, the cassava brown streak which is now in over 40 districts is increasing and farmers are losing a lot of yields. Districts in central Uganda are the most hit by these virus followed by western Uganda in the districts of Hoima, Kasese and Masindi as well as in the eastern part of the Country. The districts in northern Uganda including West Nile are the least affected.
Dr Titus Alicai, a plant pathologist involved in this research said recent studies reveal that cassava brown streak which is destroying the plant across the East African region is mostly spread by the white fly vector. According to Dr Alicai, the researchers discovered another type of virus called cassava brown streak Uganda virus which is now being spread by white flies. This Virus has spread to the central part of Uganda, western Kenya as well as western Tanzania.
Dr Alicai says that this virus is found in the leaves on which the flies feed by sucking the fluid to get the sugary substance in the young leaves. The flies therefore pick the virus from the infected leaves and transfer it to healthy plants using the same process of sucking sugar from the leaves of those plants. The researchers are now trying to improve varieties that will be resistant to the white flies because it is difficult to wipe out these flies. “What we are trying to do right now is to get varieties which are resistant to the white fly in that once a fly comes with the virus obtained from an infected planted, it will not infect this other plant,” Dr Alicai said.
The researchers obtained two cassava varieties from Latin America that are resistant to these flies. They have been carrying out research on these varieties by introducing a small piece of the virus into the cassava tissue. The researcher further picks a small piece of the leaf and puts it in a medium to form cells which will then grow into a plant in a period of one year. Once the plants are transferred to the filed site at the institute, the researcher later releases a collection of white flies on the plants. According to Dr Alicai, since the white flies in Latin America, are of different species, only one variety proved to be resistant to the flies here.
The researchers are optimistic that they will come up with varieties that are completely resistant to this disease because currently Uganda is losing a lot of money due to infected cassava. Apart from their efforts to obtain the variety that is resistant to the white fly, the researchers have also embarked on a five year project funded by Monsanto where they are testing the virus using the tobacco plant to see if it affects them before demonstrating it on the cassava plant.
This according to Dr Alicai is for purposes of generating information which his team will use for testing the disease free cassava varieties. The group is further using another method where they are applying molecular markers to introduce resistance to the cassava variety. Other activities that are not Biotech related are screening the planting materials on a large scale from various fields and so far they have obtained six tolerant clones from the virus. Dr Anthony Bua, the Team leader for the Cassava research programme advised farmers to observe the space of three to four metres when planting the materials because this will reduce the rate of infection. He also advised farmers to plant their cassava in February, June and late October which are rainy seasons.
