Kaweesi T., Kawuki R., Kyaligonza V., Baguma Y., Tusiime G., Ferguson M.E.
National Crops Resources Research Institute, Root Crop Program, Namulonge, Uganda; Makerere University, College of Agricultural and Environmental Sciences, Kampala, Uganda; International Institute of Tropical Agriculture (IITA), c/o ILRI, P.O Box 30709, Nairobi, Kenya
Kaweesi, T., National Crops Resources Research Institute, Root Crop Program, Namulonge, Uganda; Kawuki, R., National Crops Resources Research Institute, Root Crop Program, Namulonge, Uganda; Kyaligonza, V., National Crops Resources Research Institute, Root Crop Program, Namulonge, Uganda; Baguma, Y., National Crops Resources Research Institute, Root Crop Program, Namulonge, Uganda; Tusiime, G., Makerere University, College of Agricultural and Environmental Sciences, Kampala, Uganda; Ferguson, M.E., International Institute of Tropical Agriculture (IITA), c/o ILRI, P.O Box 30709, Nairobi, Kenya
Background: Production of cassava (Manihot esculenta Crantz), a food security crop in sub-Saharan Africa, is threatened by the spread of cassava brown streak disease (CBSD) which manifests in part as a corky necrosis in the storage root. It is caused by either of two virus species, Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), resulting in up to 100% yield loss in susceptible varieties. Methods: This study characterized the response of 11 cassava varieties according to CBSD symptom expression and relative CBSV and UCBSV load in a field trial in Uganda. Relative viral load was measured using quantitative RT-PCR using COX as an internal housekeeping gene. Results: A complex situation was revealed with indications of different resistance mechanisms that restrict virus accumulation and symptom expression. Four response categories were defined. Symptom expression was not always positively correlated with virus load. Substantially different levels of the virus species were found in many genotypes suggesting either resistance to one virus species or the other, or some form of interaction, antagonism or competition between virus species. Conclusions: A substantial amount of research still needs to be undertaken to fully understand the mechanism and genetic bases of resistance. This information will be useful in informing breeding strategies and restricting virus spread. © 2014 Kaweesi et al.
Article; cassava; cassava brown streak disease; Cassava brown streak virus; controlled study; field study; genotype; housekeeping gene; nonhuman; plant root; plant virus; reverse transcription polymerase chain reaction; shoot; Uganda; Ugandan cassava brown streak virus; viral plant disease; virus expression; virus load; virus resistance; disease resistance; genetics; immunology; isolation and purification; Manihot; plant disease; Potyviridae; real time polymerase chain reaction; virology; Cassava brown streak virus; Manihot esculenta; Disease Resistance; Manihot; Plant Diseases; Potyviridae; Real-Time Polymerase Chain Reaction; Uganda; Viral Load