O.A. Ariyo, A.G.O. Dixon and G.I. Atiri
Twenty five IITA-improved cassava cultivars were evaluated on the field in IITA, Ibadan for relative resistance to African cassava mosaic disease (ACMD). These cultivars were exposed to natural infection by the viruliferous whiteflies (Bemisia tabaci). ACMD incidence (DI) and index of symptom severity (ISS) calculated on a scale of 1 (no symptom) – 5 (very severe) were the two major parameters used in evaluating the relative resistance of these cultivars. The evaluation made was based on the rank sum method (i.e. adding DI and ISS ranks for each cultivar). Isu and TMS 30572 were observed to be highly susceptible to ACMV infection through this method. Clones 94/0270, 82/00058, 91/02322, 92/0326 and 92B/00061 were susceptible. Plants of clones 92/0325, 92/0342, 4(2)1425, 92/0427, M94/0177 and TME-1 were moderately susceptible. Moderate resistance was observed in plants of clones M94/0192, 92B/00068, 92/0057, 94/0237, 92/0398 while plants of clones M94/0461, 91/02324, 91B/00455, 91/02327 and M94/0583 were resistant. Clones 94/0239 and M94/0121 were highly resistant to the virus infection. Immunity as a form of resistance was observed in none of the clones screened.