Demand-Driven Technologies for Sustainable Maize ... - IITA

258faibles réactions qui indiquent la non-préférence ou l’antibiose) ou lasusceptibilité relative (caractérisée par des fortes réactions qui facilitentla colonisation) d’un génotype comparativement à un autre. Un profi lde l’ensemble des réactions à chaque génotype a été établi afi n depermettre une meilleure compréhension des différents aspects de cesinteractions. Les différents profi les ont montré que S5 9-1 a eu cingréponses allant de faibles à moyenne, ce qui indique une résistancede sa part vis-à-vis de S. calamistis. S5 20-2 au contraire, a eu uneréponse très élevée, et trois réponses moyennes, tandis que Tzmi 407en avait deux réponses moyenne, ce qui les rend très susceptiblesvis-à-vis de cet insecte. Les profi les des autres génotypes se trouvaiententre ces deux extrêmes.IntroductionStem borers are one of the major constraints to maize (Zea maysL.) production in Africa. The most important and predominant borerspecies are Chilo partellus (Swinhoe), Busseola fusca (Fuller), Sesamiacalamistis (Hmps.) and Eldana saccharina (Walker) (Usua 1968; Girling1978; Kumar and Sampson 1982; Aroga 1987a, b; PNUD/FAO1989; Cardwell et al. 1997). Strategies to reduce damage due tothese pests have, in the past, relied mainly on the use of insecticides,which are usually expensive (Seshu Reddy 1983; Kfi r 1990). In Africa,a large proportion of maize producers are small-scale subsistencefarmers. For such farmers, it is not economically or logisticallyfeasible to use synthetic insecticides. In addition, synthetic insecticideshave harmful effects on human beings and cause environmentalpollution. Air and water contamination, postharvest residues, lackof selectivity, and resurgence of resistant species are examples ofadverse effects of using synthetic insecticides (CCE 1974). Therefore,more economically sustainable strategies to pest management, such asthe use of insect resistant or tolerant genotypes, are being researchedand developed.Host-plant resistance is one of the most important components ofthe integrated pest management of the maize stem borers. Severalgenotypes resistant or tolerant to C. partellus, E. saccharina and S.calamistis have been developed (Bosque-Pérez et al. 1989; Bosque-Pérez and Mareck 1990; Kumar 1991; Ajala et al. 1995; IITA 2000).For instance, eight S5 lines have been reported as resistant and twoothers as susceptible to S. calamistis (IITA 2000). The criteria usedfor these classifi cations were leaf-feeding scores, dead hearts, stemtunnelling and the overall plant damage (Ajala and Saxena 1994;Ajala et al. 1995).According to Saxena (1969, 1985) the insect’s colonizing responsesare part of the factors determining the level of genotypic resistance