Combining ability for multiple resistance to turcicum leaf blight (Exserohilum turcicum) and maize streak virus disease

Maize foliar diseases are the most important impediments to increased maize production in Uganda. The main objectives of the studies reported in this thesis were (i) to characterise inbred lines for resistance to Turcicum leaf blight and maize streak virus disease; and (2) to evaluate three way hybrids in multi environments for performance under Turcicum leaf blight and maize straek virus disease infections. Fifty four single crosses were evaluated in two locations in the first rains of 2009. The experimental design was alpha lattice design with 2 replications in each environment. The aim was to estimate general (GCA) and specific combining ability (SCA) and investigate genotype x environment interaction. Significant GCA and SCA effects were found for both Turcicum leaf blight (TLB) and Maize streak virus disease (MSVD) incidence across environments. Inbred lines WL429-13, WL429-17 and WL429-29 showed reduced GCA effect for TLB severity while inbred lines WL429-36, WL429-33 and WL429-34 had lower GCA effects for MSVD across environments. Fifty two of the evaluated single crosses crossed to two inbred testers in first rains of 2009 to constitute three-way germplasm. These were evaluated in three locations in the second rains of 2009. The results show availability of resistant genotypes among the three-way crosses. Hybrid (WL429-16 x WL429-36) x CML444 was the most resistant to TLB and (WL429-16 x WL429- 28) x CML202 show the largest reduction in MSVD severity. Genetic variability was maintained though with low heritability estimates. Negative, but strong correlations between TLB and MSVD, and yield were detected suggesting that in general recurrent selection for resistance would improve multiple resistance and enhance grain yield among the three way crosses.