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Evaluation of Local and Elite Cassava Genotypes for Resistance to Cassava Brown Streak Disease in Uganda

Keywords: Disease pressure , resistance , root necrosis , severity , incidence

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Abstract:

Cassava production in the East African region is seriously being constrained by the devastating Cassava Brown Streak Disease (CBSD) that causes characteristic above and below ground symptoms, making cassava roots unfit for human consumption. Development of cassava varieties that are resistant and/or tolerant to CBSD is an important component in the CBSD management. Therefore, the main purpose of this study was; to evaluate both local and elite cassava genotypes for possible sources of resistance to CBSD. One hundred and sixteen cassava genotypes were screened for CBSD resistance under field conditions. The experiment was laid out using a Randomized Completely Block Design (RCBD) with three replicates at Namulonge where CBSD pressure is high. A single row plot of six plants per genotype was used. CBSD data were collected monthly for a period of 12 months. Results indicated that foliar and root incidences and severities varied significantly among genotypes (p<0.001). All the local genotypes showed foliar CBSD symptoms with incidence ranging from 0-98% and severity from 1-3.23 whereas, ten of the elite genotypes did not show foliar symptoms. The genotypes NASE 1, MM96/4271, CR 20A-1, TZ06/130, MM96/0686 and MM96/0876 were consistently associated with low CBSD as they had both foliar and root incidence and severity of zero and one, respectively and thus, can be considered parental breeding stock for CBSD resistance breeding. There was a further strong association between CBSD foliar and root symptom as most genotypes that showed foliar symptoms showed root necrosis.

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