Abstract
Nature of gene action and genetic parameters for disease resistance are important attributes in developing resistant cultivars. This provides the sustainable, economically justifiable and environmentally friendly means of controlling plant diseases. In this study 6 x 6 full diallel cross involving genetically divergent maize inbred lines was performed with the aim of developing resistant cultivars against Maize Lethal Necrosis (MLN) disease under MLN disease hot spot areas in Mlangarini, Ngaramtoni and Kiru six in the Northern Zone of Tanzania during 2015 cropping season. The experimental materials consisted of thirty single cross hybrids, six parents and two local checks. The experiment was laid down in a randomized complete block design (RCBD) with three replications per location. The general combing ability (GCA) and specific combining ability (SCA) effects were significantly different for MLND response among genotypes across all locations. The combined analysis revealed that GCA was highly significant at (P≤0.001) than SCA in all locations with mean squares of (5.551***), (1.61***) and (4.527***) for Mlangarini, Kiru six and Ngaramtoni respectively. The GCA: SCA ratios were 1.894, 1.726 and 1.403 for Mlangarini, Kiru six and Ngaramtoni respectively. The implication of GCA/SCA ratio of more than a unity proves that GCA is significant in all locations where this study was conducted. The results also revealed the presence of both additive and non-additive genetic effects, with the former more pronounced than the later. This implies that developing composite variety will be the better option in combating the disease. However the best cross was observed between CML 144 X CML444 with mean square -0.10, -0.45* and -0.18* for Mlangarini, Kiru six and Ngaramtoni respectively. Key words: Diallel cross, general combing ability (GCA), heritability, Maize Lethal Necrosis disease (MLND), specific combining ability (SCA), Zea mays.
Highlights
The popularity of maize in Africa has been increasing to the extent of replacing traditional crops like sorghum and millet (DeVries and Toenniessen, 2001)
Whereby the mid Analysis of variance showed highly significant differences among genotypes for Maize Lethal Necrosis (MLN) response indicating the presence of sufficient genetic variation among treatments (Table 1)
Both general combing ability (GCA) and specific combining ability (SCA) were determined in respect to disease response against maize lethal necrosis virus in the study areas
Summary
The popularity of maize in Africa has been increasing to the extent of replacing traditional crops like sorghum and millet (DeVries and Toenniessen, 2001). Despite the importance of maize as the main staple crop, average yields in farmers’ fields are relatively low averaging 1.2 metric tons per hectare compared to the estimated potential yields of 4 to 5 metric tons per hectare (WEMA, 2010). Infection rate and damage can be very high seriously affecting yields and sometimes causing complete crop loss (Wangai et al, 2012). The disease is caused by the co-infection of Maize Chlorotic Mottle Virus (MCMV) and any potyvirus group such as Sugar Cane Mosaic Virus (SCMV)
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