| A study was carried out at two locations in Uganda to investigate the nature of resistance in inbred H99 and the interaction of monogenic and polygenic resistance to NLB. In order to obtain appropriate comparison of responses of different maize genotypes to northern leaf blight (NLB), inbred line H99 was crossed with nine genotypes of varying levels and types of resistance to NLB. Combination of monogenic and polygenic resistance in single genotypes was investigated by assessing the effect of Exserohilum turcicum race 0 on the number of lesions and percent leaf area affected (PLAA). Non-orthogonal contrasts were carried out to compare the effects of resistance types, individually or in combination, in reducing lesion number and PLAA.;The genotypes that had neither monogenic nor polygenic resistance were the most susceptible. Addition of the Ht gene to these genotypes reduced the disease intensity only under low disease epidemics. Polygenic resistance reduced both the lesion number and PLAA. In genotypes where polygenic resistance was already high, for example in Mo17 and Babungo 3, crossing with H99 offered no further advantages. Combination of monogenic and polygenic resistance was beneficial only under low disease epiphytotics.;Variance component analysis, heritability estimates and estimation of the minimum number of genetic factors controlling resistance to NLB were computed from A619 x H99 F... |
