SCREENING ELITE CASSAVA LINES FOR THEIR RESPONSE TO CASSAVA MOSAIC AND BROWN STREAK VIRUSES

Abstract

Cassava Mosaic Disease (CMD) and Cassava Brown Streak Disease (CBSD) have been the major biotic factors limiting potential yield in cassava production for decades. This research was conducted to investigate the response of elite cassava lines to CMD and CBSD under field conditions, evaluate the pathogenicity levels of CMD and CBSD on elite cassava lines under greenhouse conditions, and assess the genetic diversity of elite cassava lines for their response to CMD & CBSD using sequence characterized amplified region (SCAR) markers. The screening was done under a hot-spot field in RCBD with five test lines against CMD and CBSD, where two of the lines were susceptible and resistant checks while three were mutant lines; scoring was done at a scale of 1-5. Influence of CMD on test lines under field conditions was unique from site to site, with Site× DAP having (p<0.05), ML ×DAP and Si× ML ×DAP had a probability of (p>0.05), with tolerance quality of these elite lines to the pathogen species across the sites. CBSD posted interaction; Site× DAP, ML ×DAP (p <0.05), and Si× ML ×DAP (p>0.05). The means especially (CAS1, CAS2, CAS3) were found to be below 2.0 in all the sites for both diseases and posted a low severity mean, thus low infection with both shoot and root resistance. Only parental lines had root infection with brown-ringed roots, especially KME4. Field trials showed elite material with a low severity range between 2.5- 3.0. Tolerance to CBSD inoculum was expressed by CAS1 & CAS2 at a severity level between 2.5 -3.0 while CAS 3. DNA amplification found no CBSD and CMD alleles in CAS1 while they had faded traces on CAS2 and CAS 3, but the same was found in checks (KME3, KME4). However, inadequate genetic sources for breeding remain a challenge in mitigating the two viral diseases.