Evaluation of cassava varieties for cassava mosaic disease resistance jointly by agro-inoculation screening and molecular markers

Abstract

The whitefly-transmitted cassava mosaic disease (CMD) has become a potential threat to cassava
(Manihot esculenta Crantz) cultivation in ASEAN countries because of its devastating impact on
cassava and overgrowth of whitefly vector regionally. To reduce the risk caused by the disease, it is
necessary to evaluate the capacity of major cassava germplasms for CMD resistance to guide local
farmers in adopting CMD-resistant cultivars once CMD epidemics occur. After agro-inoculation
mediated infection of plantlets of collected cassava cultivars from China, Thailand and other ASEAN
countries, the 18 cultivars tested developed various levels of CMD symptoms, indicating a lack of
resistance to CMD. There was a positive association between symptom severity scores and
accumulation levels of viral DNA in the different cultivars tested. The molecular markers RME1, SSRY28
and/or NS158, which link with the CMD resistance loci CMD2 in cassava, were found in only three
cultivars (11Q, T7 and N13) with moderate resistance to CMD. Our study suggests that CMD-resistance
germplasms should be introduced from Africa.