Assessement and Genetic characterisation of Maize (Zea mays L.) Germplasm for leaf blight(Helminthosporium turcicum pass.)

Abstract

Maize leaf blight caused by the fungus Helminthosporium turcicum (Exerohilum turcicum) is one of the constraints affecting maize production and thereby eroding income and food security in Zambia and the Southern African region. Maize leaf blight severity on susceptible varieties can range between 40-70% plant coverage and can reduce maize yields by up to 60% when infection is high. Six FI maize hybrids and their p2 populations were evaluated for leaf blight resistance in 2006 and 2007 at the Golden Valley Agricultural Research Trust, Chisamba, Zambia. They were artificially inoculation with the pathogen. Disease resistance parameters used to assess the disease included, disease severity scores, percent affected ear leaf area, number of lesions, lesion sizes, incubation periods, area under disease progress curve and apparent infection rates. From the FI'S evaluation, disease resistance parameters indicated that hybrids J34-2 and J34-4 were the most susceptible and J34-1 and J34-3 were most resistant hybrids respectively. All f-i populations showed continuous variation for leaf blight resistance. Variability parameters namely genetic coefficient of variation (GCV), broad sense heritability (h2b) and genetic advance (GA) as measured by the resistance parameters were used to determine the gene action for leaf blight resistance on individual populations. The variability parameters revealed that in populations J34-1, J34-2, J34-3 and J34-5 leaf blight resistance was under additive gene action, while in populations J344 and J34-6 they revealed that leaf blight resistance was under non additive gene action. In all cases genotypic correlations in general, were higher than the corresponding phenotypic correlations, indicating little influence of the environment on any inherent association among the traits studied. Male flowering dates were found to be significantly but negatively correlated with most disease resistance parameters, indicating that such a trait could be used indirectly for the improvement of leaf blight resistance in maize. The inferences of the results of the present study and possible implications in maize breeding for leaf blight resistance have been discussed.