Kiarie Njoroge

Genetic analysis of early-maturing maize (Zea Mays L.) inbred lines under stress and nonstress conditions

ABSTRACT Early-maturing maize (Zea Mays L.) germplasm developed from diverse sources has the potential for use in developing maize hybrids suitable for increasing maize production in the dry ecologies of eastern Africa. A diallel study was conducted to estimate general combining ability (GCA) of 12 early-maturing maize inbred lines, identify potential single-cross hybrids for use as parents, assess genetic diversity among the inbred lines, and relate genetic distance to specific combining ability (SCA) and hybrid performance. Sixty-six F1 diallel hybrids were evaluated under optimal and drought stress conditions at four locations in Kenya and Uganda. The parental inbred lines were genotyped using 94 single nucleotide polymorphism (SNP) markers. Additive gene action was more important than nonadditive gene action for inheritance of grain yield (GY) under optimal conditions. However, nonadditive gene effects were more important in the inheritance of GY under drought and across all environments. Inbred lines CKL0722, VL058014, and CZL0724 were among the best with positive GCA effects for GY across both optimal and drought stress conditions. The correlation between SCA and both genetic distance and F1 GY was significant under both drought stress and across all environments. Inbred lines with desirable GCA effects for GY and other agronomic traits and hybrids with good performance under both optimal and drought stress conditions are potential parents for development of various types of high-yielding, stress-tolerant, and early-maturing hybrids.

Genetic Components of Grain Yield Stability in Maize Diallel Crosses

ABSTRACT In sub-Saharan Africa, maize (Zea mays L.) is produced in very diverse environments, which often results in complex genotype-by-environment (G × E) interactions. The aim of the study was to identify genotypes with broad and specific adaptation and high-performance environments that offer the best discrimination for selection and assess parents’ contribution to hybrid stability. Sixty-six F1 maize hybrids developed from a 12 × 12 half-diallel were evaluated at four locations in Kenya across two seasons to study the G × E patterns for grain yield and other agronomic traits. The genotype and genotype-by-environment interaction (GGE) biplot method was used for graphical display of data. Stability of combining ability effects was examined using rank variance and Wricke’s ecovalence. Environments contributed moderately (44%) to yield variability while the effects of G × E interaction (23%) and genotypes (21%) were almost equal. The eight environments were divided into two mega-environments, the first representing medium-transitional locations, whereas the second mega-environment had medium-late locations. Hybrid 6 (Z419 × MUL114) and hybrid 22 (MUL71 × Osu23i) were the best genotypes for the first and second mega-environments, respectively. Hybrid 47 (CML509 × C92) was the most stable and highest yielding hybrid across environments and can be recommended for cultivation in both mega-environments. Inbred CML539 displayed the most stable general combining ability. Crossover interaction was found to exist, which signified the need to breed for both broad and specific adaptations.