Screening Cassava Genotypes for CBSV and UCBSV Resistance

Eleven cassava genotypes selected from Uganda and Tanzania were screened for field resistance to both UCBSV and CBSV in Uganda. Tanzanian genotypes reported to be resistant/tolerant in Tanzania were AR40-6, NDL06/132, Kiroba and Namikonga (also known as Kaleso), and Ugandan genotypes reported to be tolerant in Uganda were NASE 14 (MM96/4271), 72-TME 14 (NASE 19), NASE 1 and TZ/130 (Table 5). Genotypes Albert from Tanzania, and Kibaha and TME 204 from Uganda were included as susceptible controls. Genotypes from Tanzania were obtained as virus-free tissue culture plantlets while those from Uganda were sourced as stakes from CBSD disease-free areas. All planting material was diagnosed as free of (U)CBSV prior to planting. Tissue culture plantlets were hardened according to [38 ]. Field trials were established in the first rains (March – May) of 2012 at National Crops Resources Research Institute (NaCRRI), Central Uganda (lat/lng: 0.529, 32.612, Alt 1222 m), an area with high CBSD and whitefly pressure [39 (link)]. Test genotypes were established in two row unreplicated plots each containing 10 plants with a spacing of 1 m × 1 m. Each plot was separated by a CBSV/UCBSV infected spreader row of TME 204. Plants of TME 204 used in the spreader rows were obtained in fields that had a CBSD incidence of 100% and a mean severity of 4 and 4.5 for shoot and root necrosis respectively. This selection was done to ensure that infector line had high viral load to effectively augment CBSD pressure. The genotypes were grown for 12 months under rainfed conditions on a sandy-loam soil and no fertilizer or herbicide was applied. Regular weeding was undertaken.