Resistance levels of cassava landraces to CMD, CBSD and vector whiteflies in Malawi

Abstract Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) have been two major threats to cassava production in eastern and southern Africa. This study was designed to identify CMD- and CBSD-resistant cassava landraces and farmer-preferred varieties in Malawi for effective disease control. Thirty cassava landraces were collected from 17 districts across Malawi and evaluated for disease resistance a field experiment at the Chitala Research Station in a randomized complete block design (RCBD). Cultivars Mbundumali and Pwani were used as susceptible and resistant controls, respectively. Data collected on foliar and root disease symptoms indicated that CMD was more prominent than CBSD during the study. Cultivars Pwani, Mkumba, R23-Sangwala, Sagonja, R31-Kamphunobi, R33-Chimphuno, R76-Kamphuno, MZ126, and R63-2020 showed relative dual resistance to both CMD and CBSD with the highest incidence of 25 and 18%, respectively. Some cultivars showed resistance to one disease and not the other. The lowest cumulative number of whiteflies (0.68 per plant) was observed on Pwani while the highest was seen on R42-Mwenemisuku with 6.33 per plant. However, various cultivars supported varied numbers of whiteflies and nymphs. Assessing relative virus quantities of the prevailing viruses, East African cassava mosaic virus (EACMV) and Cassava brown streak virus (CBSV) indicated that Pwani, Mkumba and Sagonja supported lowest amount of EACMV and CBSV. Our results collectively identified the presence of dual-resistant cassava which can be further exploited for managing both CMD and CBSD in Malawi.