COMPONENTS OF RESISTANCE OF CASSAVA TO AFRICAN CASSAVA MOSAIC-VIRUS

Components of resistance of cassava (Manihot esculenta) to African cas sava mosaic virus (ACMV) and their interrelationships were confirmed a nd quantified in a series of experiments at Adiopodoume (Ivory Coast, West-Africa). The response to virus infection and to Bemisia tabaci in festation of a large collection of cassava, including local cultivars and others derived from inter-specific M. glaziovii hybrids was assess ed. A consistent correlation was found between virus titre, symptom in tensity, disease incidence and non-systemicity (recovery) which sugges ts that they are different expressions of the same genetic resistance. By contrast, there was no correlation between whitefly infestation an d incidence of ACMV, suggesting that resistance to virus and vector ar e determined by two distinct genetic mechanisms. Several improved cult ivars derived from inter-crossing cassava with M. glaziovii as well as some local cultivars were highly resistant and combined low susceptib ility, low symptom intensity, low virus content and high level of reco very. Although yield losses ranged from 10% to 30% in such resistant c ultivars, the combined effect of high field resistance and high rate o f recovery lead to low disease incidence and limited yield losses, eve n in areas of high infection pressure such as Adiopodoume.