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

254Signifi cant correlations were found between some diseases andLAI. In 1995 in the HF and 2004 in the WHL, the negative correlationsof LAI with R. solani and B. maydis, S. macrospora and physiologicalspot suggested that despite the presence of these pathogens onthe leaf surface, their effects may have been diluted by E. turcicum,which was negatively correlated with the pathogens. E turcicum andP. polysora were associated with leaf destruction. This pattern wasnot apparent in 2004, but B. maydis, S. macrospora and P. polysorawere inversely correlated to E. turcicum. This relation suggested thatwhile some disease organisms coexist in the same ecological areas,there are situations where better-adapted ones displace some others.Understanding the type of relationship may be benefi cial for planningthe most effective control strategies.From the observations in 2004, it is clear that the incidence andseverity of leaf diseases of maize have decreased signifi cantly from theearly 1990s. The National Cereals Research and Extension Project,a USAID-funded project, has released several maize varieties withresistance to these pathogens. Grey leaf spot, which was a minorproblem in 1995, has taken the lead over Phaeosphaeria leaf spotand highland blight and today is a major leaf problem in all themaize producing areas of the WHL. These diseases have not beenresearched to any appreciable extent in Cameroon. In addition, earrots have become a major problem to maize producers. The climaticchanges (especially unpredictable rainfall), the post-harvest agriculturaltechniques (harvesting takes place during the peak rain period in theWHL), and the poor drying and storage conditions favour the infectionof grains by several fungi and possible contamination by mycotoxins.These secondary metabolites are known to be public health problemsin localities where maize is consumed as staple food.Annual maize production in Cameroon has not increased at theexpected rate. This is attributable to the technological packages releasedso far, which are probably inadequate, and the cost of inputs (Fajemisin1985; NCRE 1994; Ngoko et al. 2002). Intensifi ed food productionhas led to ineffective crop rotation or fallowing. Continuous maizecultivation in areas where several diseases are endemic contributes topathogen build-up. Though the type of synergy that occurs amongthe different maize pathogens is not yet well elucidated, individualpathogens may cause less destruction on plants and plant partscompared to the association of several fungi (Cardwell et al. 1997).The association of several maize pathogens in the fi eld needs to befurther investigated to determine whether these fungi cause diseasein succession and to what extent synergism occurs. Results of thepresent study, and those of earlier studies (Cardwell et al. 1997), haveidentifi ed hot spots for major diseases where screening for resistance