Response of cassava cultivars to African cassava mosaic virus infection across a range of inoculum doses and plant ages

Cassava production in Africa is constrained by cassava mosaic disease (CMD) that is caused by the Cassava mosaic virus (CMV). The aim of this study was to evaluate the responses of a range of commonly cultivated West African cassava cultivars to varying inoculum doses of African cassava mosaic virus (ACMV). We grafted 10 cultivars of cassava plants with different inoculum doses of CMV (namely two, four, or six CMD-infected buds) when the experimental plants were 8, 10, or 12 weeks old, using non-inoculated plants as controls. Three cultivars showed disease symptoms when grafted with two buds, and four cultivars showed disease symptoms when grafted with four or six buds. Most cultivars became symptomatic six weeks after inoculation, but one (‘TMS92/0326’) was symptomatic two weeks after inoculation, and two (‘Ntollo’ and ‘Excel’) were symptomatic after four weeks. Root weight tended to be lower in the six-bud than in the two-bud dose, and disease severity varied with plant age at inoculation. These results indicate that the level of CMD resistance in cassava cultivars varies with inoculum dose and timing of infection. This will allow appropriate cultivars to be deployed in each production zone of Africa in accordance with the prevalence of CMD.

非洲木薯生产受木薯花叶病（Cassava mosaic disease, CMD）制约，该病由木薯花叶病毒（Cassava mosaic virus, CMV）引发。本研究旨在评估一系列西非常见栽培木薯品种对不同接种剂量的非洲木薯花叶病毒（African cassava mosaic virus, ACMV）的响应。当试验植株生长至8、10或12周龄时，我们以不同剂量的CMV接种木薯——即分别嫁接2、4或6个携带CMD的芽条，并以未接种的植株作为对照组。嫁接2个带毒芽条时，有3个品种出现病害症状；嫁接4或6个带毒芽条时，则有4个品种显现病症。多数品种在接种后6周出现症状，但有一个品种（‘TMS92/0326’）在接种后2周即显现症状，另有两个品种（‘Ntollo’与‘Excel’）在接种后4周出现症状。相较于2个芽条的接种剂量，6个芽条剂量下的块根重量普遍更低，且病害严重程度随接种时植株的龄期发生变化。上述结果表明，木薯品种对CMD的抗性水平随接种剂量与感染时机而异。该发现可指导根据非洲各产区的CMD流行情况，部署适配的木薯品种。