Friday, November 1, 2013

Study offers tip into the complexity of begomo viruses in West and Central Africa

Dr Leke in the virology lab
A study by Dr Walter Leke, IITA virologist, has revealed a huge complexity of begomoviruses and DNA satellites previously largely unknown in West and Central Africa.
Begomoviruses are plant-infecting viruses, which are transmitted by the whitefly vector Bemisia tabaci. They have a genome of single-stranded DNA that consists of either a single (monopartite) or two components (bipartite) with a component size of approximately 2.8kb. Many monopartite begomoviruses in the Old World have been found to be associated with betasatellite and alphasatellite molecules, which are about half the size of their helper begomovirus genome. Betasatellites have been shown to be necessary for inducing severe disease symptoms.
During the West Africa Seminar series, Dr Leke spoke on “Molecular characterization of begomoviruses and associated satellites in Cameroon – implications for plant virus research in Africa.”
The study found that in Cameroon, B. tabaci has been associated with suspected begomovirus infections in many crop and weed species. However, in spite of their growing importance, only begomoviruses infecting cassava have been studied in Cameroon in any detail.
Dr Leke said the study was inspired by the need for additional information on diversity and distribution of begomoviruses and satellites in vegetable crops and dicotyledonous weeds, which likely serve as virus reservoirs.
In field studies, a high incidence of okra leaf curl disease was found in Cameroon. Sequencing of viral genomes showed that the okra plants were infected by viruses of two previously known begomovirus species (Cotton leaf curl Gezira virus and Okra yellow crinkle virus) as well as a new recombinant begomovirus species (Okra leaf curl Cameroon virus). In addition, a betasatellite (Cotton leaf curl Gezira betasatellite) and two alphasatellites (Okra leaf curl Mali alphasatellite and Okra yellow crinkle Cameroon alphasatellite) were identified. Also tomato plants with leaf curling were shown to contain isolates of a new begomovirus, Tomato leaf curl Cameroon virus, and an alphasatellite, Tomato leaf curl Cameroon alphasatellite (ToLCCMA).
Sequence analyses of begomovirus complexes infecting the weed, Ageratum conyzoides, showed that they were infected by isolates of a new begomovirus (Ageratum leaf curl Cameroon virus), two new betasatellites (Ageratum leaf curl Cameroon betasatellite and Ageratum leaf curl Buea betasatellite), an alphasatellite (ToLCCMA), and two types of defective recombinants between a begomovirus and ToLCCMA.
Dr Leke concluded that with this high diversity, recombination potential and transmission by B. tabaci, begomoviruses, and their associated DNA satellites pose a serious threat to crop production in the region and the African continent as a whole.

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