Breeding Maize For Resistance To The Fall Armyworm (Spodoptera Frugiperda J.e. Smith), Improved Yield And Yield-Related Traits.
Maize production and productivity in sub-Sub-Saharan Africa (SSA), including Zambia, has been severely threatened by the recent arrival of the fall armyworm (FAW) (Spodoptera frugiperda J.E. Smith). Several strategies have been proposed to control FAW. Integrated pest management (IPM), emphasizing host-plant resistance, has been identified as the most sustainable approach. However, validated and locally-adapted FAW-resistant maize cultivars have not yet been developed and deployed in sub-Saharan Africa. The aim of this research was to develop FAW resistant, farmer-preferred and locally adapted maize varieties. The specific objectives of this study were: (1) to identify farmers' maize production constraints and preferred traits, and to assess farmers' perceptions of the impact of FAW on maize production and productivity in Zambia; (2) to screen a diverse population of maize genotypes for FAW resistance, yield, and yield-related traits by phenotyping and genotyping, to select the most promising genotypes for crossing; (3) to optimise the methods for laboratory rearing of FAW, and to conduct artificial screening of promising maize genotypes under controlled conditions and artificial FAW infestation; (4) to determine the level of genetic diversity for agronomic and FAW-related traits among the test population of maize genotypes using SNP markers complemented by phenotypic information to identify suitable parents for developing FAW-resistant breeding populations; and (5) to determine the nature of gene action conditioning FAW resistance, yield, and yield-related traits through combining ability analysis, and to identify the most promising crosses for continued evaluation in FAW resistance breeding. In the first study, participatory rural appraisal (PRA) surveys were conducted in two FAW affected districts in Zambia in 2017 and 2018, using semi-structured questionnaires, preference ranking and focus group discussions. The high cost of fertilizers, the limited availability of agricultural lands, insect pests, and drought stress were reported by 73, 55, 38 and 36.6% of the respondents, respectively, as the main production constraints. There were significant differences (X2 = 12.415; p = 0.002) in the severity of FAW infestation between the two surveyed districts in 2017. Farmer-preferred traits of maize were insect pest resistance, early maturity, drought tolerance and market price of the grain. FAW resistance, drought tolerance and grain yield performance are the key drivers for maize variety development and deployment in Zambia. In the second study, two sets of diverse maize germplasm were assessed for FAW resistance and desirable yield-related traits in a FAW-affected area in Zambia. Set I and Set II, containing 60 and 253 maize genotypes, respectively, were selected, based on their agronomic potential and adaptability. Highly significant differences (P < 0.001) were detected among the test genotypes for FAW leaf damage (FLD), FAW cob damage (FCD) and agronomic traits. The lowest levels of FLD and FCD were 8.87% and 5.36%, recorded for genotypes CML304-B and CML442, respectively. Five principal components (PCs) accounted for ≥80% of the total variation associated with reduced anthesis-silking interval (ASI), plant height, FLD and FCD, desirable ear aspect and grain yield. Genotypes such as Pool 16 and ZM 7114 from Set I, and CZL1310c, CML444-B, CZL15220 and TL1512847 from Set II had low mean FCD and FLD values, suggesting higher levels of FAW resistance. Grain yield was negatively correlated with mean FLD (r = 0.18, p <0.05), and FCD (r = 0.15, p < 0.05). Promising maize genotypes, including CZL1310c, CML444-B, CZL15220, TL1512847 and CML491, were selected for their low mean FLD and FCD, earliness to flowering and high grain yield potential. These genotypes should be useful in developing tropical and sub-tropical maize breeding populations with partial FAW resistance and yield gains. The third study optimised laboratory rearing and