Degeneration in quality of cassava planting material due to infection by cassava brown streak viruses
This study aimed at quantifying degeneration of cassava planting materials as a result of infection by CBSVs. Four cassava varieties (NASE 14, NASE 15, NAROCASS 1 and TME 204) were evaluated for their responses and degeneration due to CBSD at six locations (Namulonge, Nakasongola, Abi, Ngetta, Serere, and Kabarole). Varieties were arranged in a randomized complete block design and data for two seasons (2014-2015 and 2015-2016), collected monthly on CBSD severity, incidence and whitefly populations. Relative CBSVs concentration over time were determined in the test varieties using quantitative real time PCR. Collected CBSD data were used to determine degeneration of cassava varieties. The number of CCs for complete degeneration of cassava varieties was estimated using a model. Significant variation in incidence and severity among varieties was observed (p ≤ 0.05). Within the first CC, TME 204 accumulated the most CBSD, reaching 2.8 and 75.1% mean severity and incidence respectively. NAROCASS 1 was the most tolerant with 2.6 and 12.8% mean severity and incidence respectively, in the first CC. Varieties tested tended to accumulate more CBSV than UCBSV. In conclusion, varieties varied in rate and extend of degeneration due to CBSVs and this was influenced by CBSD and whitefly pressure in a location. Variety NAROCASS 1 was the most resilient to CBSD degeneration, even after 3 CCs of production under high disease pressure. Therefore, NAROCASS 1 is recommended for wide dissemination and similar varieties should be developed to ensure clean seed system and sustainable CBSD management.