Levels of host plant resistance to CMD and yield efficacy of RNAi transgenic cassava lines

Abstract

Cassava (Manihot esculenta Crantz) is an important food crop in sub-Saharan Africa (SSA). However, the crop is significantly affected by diseases, particularly the viral Cassava Mosaic Disease (CMD), which is responsible for subduing tuber yields to levels persistently lower than national demand. Moreover, management of viruses causing the disease has been complicated by high diversity from continuous recombination, which complicates breeding process of resistant varieties, coupled with rapid breakdown of natural resistance. The objective of the present study was to evaluate resistance levels of transgenic treated cassava lines as a potential strategy for managing CMD effectively in Kenya. Treatments included 11 RNAi transformed lines and one non-transformed control. In disease progression, transgenic lines; 74, 115, 141, 145 and 157 showed CMD symptoms within first four months after planting. Hence, these lines were purposively not selected for subsequent evaluations. From the CMD viruses detected in the lines, EACMV was the highest (88.9%); whereas ACMV-SEV was the lowest (59.3%). The viral load was highest in line 167; and the lowest in line 166. In terms of CMD resistance, line 166 had the highest level (64.43%); whereas the non-transformed 60444 line had the lowest (24.44%). In terms of yielding efficacy, 166 and 129 had the highest (13.53%), each with line 133 having the lowest at 4.05%. These findings demonstrate a varying trend in resistance levels of the transgenic lines; a scenario that calls for further studies to track the stability of the trait towards its potential use in CMD alleviation.