Screening of selected cassava genotypes for resistance to Cassava Brown Streak Disease by mechanical grafting in Southern Mozambique

Cassava brown streak disease (CBSD) is a major biotic stress of cassava in Southern, Eastern and Central Africa. It is caused by two virus species; the Ugandan cassava brown streak virus (UCBSV) and the cassava brown streak virus (CBSV). The CBSV is the most aggressive virus of the two. The disease can effectively be managed by exploiting host plant resistance through identification of tolerant and/or resistant genotypes. The aim of this study was to screen and identify genotypes resistant to CBSD among selected cassava lines as well as to determine the effect of CBSD on cooking time and dry matter content. Ten CBSV graft-inoculated genotypes were grown in a randomized complete design with four replicates. Data were collected from two weeks after inoculation up to nine months. Results indicated that there was no immune genotype. Genotypes exhibited different forms of response ranging from dilatory, tolerance, discriminatory and true resistance. Foliar and root severity varied significantly among genotypes (P<0.05). A weak positive correlation (r=0.0593 P>0.05) between foliar and root severity was observed. The CBSD did not have a significant effect on Dry matter content (DMC) but significantly affected cooking time with a point increment in root severity increasing cooking time by 6.4 minutes. Genotypes Amarelinha, Cucci, Munhaca, Mukalane, Timbilu and Fpo were classified under resistant category thus should be considered as breeding stock for CBSD resistance given that they displayed different levels of resistance to CBSV.