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

252Table 8. Correlation matrix between leaf area infected (LAI) and individualpathogens in the WHL of Cameroon in 2004.LAI Et Pha Cz Phy Pspt SmLAI 1.00E. turcicum 0.63*** 1.00Pha.maydis 0.44*** 0.27*** 1.00C. zeae-maydis 0.28*** -0.22* 0.16* 1.00Phy. maydis 0.11* 0.17 0.21 -0.34** 1.00Pspt -0.08* 0.08 -0.11 -0.34** 0.23 1.00S. macrospora -0.34** -0.33*** -0.16 0.14 0.15 0.36 1.00Et= Exserohilum turcicum; Pha = Phaeosphaeria maydis; Cz= Cercospora zeae-maydisPhy =Physoderma maydis; Pspt =physiological spot; Sm =Stenocarpella macrosporaE= Exserohilum; Pha= Phaeosphaeria; C= Cercospora; Phy= PhysodermaS= Stenocarpella* significant at P=0.05, **significant at P=0.01, and ***significant at P=0.001Table 9. Distribution of maize ear rots in the WHL of Cameroon in 2004.Diseases Incidences (%)Mifi Noun Mbiyeh BaliFusarium rots 25 20 15 10Diplodia rots 15 10 5 10on mature leaves in all the locations of the HF. Although several earlierstudies (Foko 1973; Praquin 1976; Timti 1980; Ngoko 1994; Cardwellet al. 1997) had reported the occurrence of many maize diseases inCameroon, only a few were found with high incidence and severity inlocalized areas.The severity of these diseases varied with years and locations.Phaeosphaeria maydis, which was reported to be important in 1993with 80% prevalence in previous maize disease surveys (Ngoko 1994),was no longer found in 2004. This leaf spot was displaced almostentirely by grey leaf spot in the WHL. Though many diseases remainedzone specifi c, highland blight was found in the HF, as had been notedpreviously in the zone (Buddenhagen 1985). This disease organism,therefore, appears to have spread out of its optimum environment,which, traditionally, is believed to be relatively cool, humid mid- andhigh altitudes. However, the disease was found at a low incidence andseverity in the HF, unlike in the WHL.Differences in the results of the maize disease surveys carried outin Cameroon may have been due to several factors. Several maizedisease surveys conducted in the early stages utilized survey techniquesthat were different from one team to the other. Some were systematicwith stops at regular intervals, others were carried out in randomlyselected fi elds, or in localized fi elds and experimental research sites.Surveys carried out in the 1970s and 1980s were on a very smallscale, while surveys carried out in the 1990s covered almost the entire