Sources of resistance to and spread of Cercospora zeae-maydis from inoculum source in maize

Two field experiments were conducted to evaluate the performance of 142 progenies of Vo613Y x Pa405 bred in Ohio, USA for resistance to gray leaf spot (GLS) and study the spread of GLS form inoculated foci at two locations in central Uganda over three maize growing seasons. The study aimed at identifying sources of resistance of GLS and studying GLS spread in maize of different resistance levels. The performance of the 142 F 2:3 progenies form ohio, USA were evaluated for resistance under artificial inoculation with Cercospora zeae-maydis in Uganda in the first cropping season of 1999. The resistant parental line Vo613Y is a south African inbred derived form a synthetic population while Pa405 is a susceptible US inbred. Two local checks, Longe 1, moderately resistnt and susceptible open pollinated popcorn cultivators were included in the study. The performance of the progenies at a mid-altitude location in central Uganda have revaled that although most of the progenies were resistant to C.zea-maydis the main focus of the study, they succumbed to severe attack by Exserohilum turcicum and maize streak virus, other important maize foliar disease in the country. In comparison to disease to disease development on the local susceptible and resistant checks, 85 of the 142 progenies were rated ‘’resistant’’ to C.zeae-maydis with a rating of less than 22.9 percentage ear leaf area affected (PELAA). Of these 35 were highly resistant with a rating of less than 6.6 PELAA and only 9 on the progenies exhibited area under disease progress curves greater than the local susceptible check and were therefore considered very susceptible to gray leaf spot. Therefore, the results of temperate germplasm evaluation in Uganda that local adaption is necessary in selecting for varieties resistant to major maize foliar disease across macroeconomic environments. In the second experiment, spatial-temporal spread of gray leaf spot on maize caused by Cercospora zeae-maydis was studied in two locations in central Uganda. Gray leaf spot development was assessed for three cropping seasons at varying distances 0.75m to 5.25 form inoculated foci on two open pollinated maize varieties. In all the seasons, disease spread was adequately depicted by both power and exponential models. Distance form inoculums focus significantly (P< 0.05) affected leaf damaged but the effect of direction from inoculated focus was variable depending on the season, location and cultivator. Thus depending on the location and seasonal variations, genotypic effect greatly affect severity of gray leaf spot. The main effect of cultivator was highly significant (P<0.001) for intercept (a) but not significant for slope (b) of the linearized power disease gradient for the number of lesions on the ear leaf. The results indicate that the maize genotype affects both the progress and spread of gray spot. The rapid flattering of the disease gradient was indicative of long distance dispersal of C.zeae-maydis in tropical environments unlike those in temperate environments.