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Restricted genetic variability in elite tropical maize germplasm has raised concerns about the potential to develop higher yielding and stress-tolerant varieties. Elite temperate germplasm has high levels of genetic diversity for yield, drought tolerance and earliness. The objective of this study was to identify temperate maize inbreds that could enhance the grain yield potential, drought tolerance and high plant density tolerance of adapted tropical germplasm. Two hundred and forty-three temperate inbreds with expired Plant Variety Protection Act certificates from the USA were crossed to three CIMMYT single-cross testers. The three-way testcrosses were evaluated under high density, optimal, low nitrogen and managed drought conditions. Among the outstanding exotic temperate inbreds were HB8229, W8304, LH198 and PJH40 from the stiff stalk group, and LH159, LH214, and LH23Ht from the non-stiff stalk group. Of the highest yielding testcrosses, 65% were heterotic group A-lines, 30% heterotic group B-lines, and 5% were AB-lines. Although the testcrosses were more susceptible to diseases, their grain yield was comparable to the commercial checks, especially under managed drought and high-density conditions. Temperate lines also induced earliness and shorter plant stature to the three-way crosses. [ABSTRACT FROM AUTHOR]

Despite the development of quality protein maize (QPM) genotypes with increased lysine and tryptophan levels, there is still a controversy on the yield potential of QPM genotypes compared to non-QPM genotypes. The objective of this study was to compare the QPM hybrids with non-QPM hybrids for grain yield and related traits and to determine if the QPM trait caused yield reduction in tested environments. A total of 126 hybrids were developed by crossing 32 inbred lines (22 QPM and 10 non-QPM) with two QPM and two non-QPM testers, using a line x tester design, and these were evaluated with four hybrid checks (two QPM and two non-QPM) at 13 locations in South Africa and Zimbabwe. Significant differences were observed among the hybrids for almost all the traits, indicating that superior hybrids could be identified and selected. Significant genotype by environment interaction effect was detected for almost all the traits which indicated that hybrids performed differently across the tested environments. When average yield for QPM and non-QPM was compared across the 13 sites, the yield reduction was 9.34% due to the QPM trait. Decreased ear placement and increased ear aspect could have contributed to this reduction. Yield reduction was 13% for the two QPM testers crossed with lines compared with means of crosses with two non-QPM testers. The best performing hybrid was a QPM genotype (entry 41), but only four of the top 20 hybrids were QPM. Though most crosses indicated a substantial yield loss due to the QPM trait, the top performing hybrid being a QPM indicates the possibility of yield potential improvement in QPM genotypes. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is the main staple cereal food crop cultivated in southern Africa. Interactions between grain yield and biochemical traits can be useful to plant breeders in making informed decisions on the traits to be considered in breeding programs for high grain yield and enhanced quality. The objectives of this study were to estimate the heritability of grain yield and its related traits, as well as quality traits, and determine the association between quality protein maize (QPM) with non-QPM crosses. Grain yield, and agronomic and quality trait data were obtained from 13 field trials in two countries, for two consecutive seasons. Significant genotypic and phenotypic correlations were recorded for grain yield with protein content (rG = 0.38; rP = 0.25), and tryptophan with oil content (rG = 0.58; rP = 0.25), and negative rG and rP correlations were found for protein with tryptophan content and grain yield with tryptophan content. Path analysis identified ear aspect, ears per plant, and starch as the major traits contributing to grain yield. It is recommended that ear aspect should be considered a key secondary trait in breeding for QPM hybrids. The negative association between grain yield and tryptophan, and between protein and tryptophan, will make it difficult to develop hybrids with high grain yield and high tryptophan content. Hence, it is recommended that gene pyramiding should be considered for these traits. [ABSTRACT FROM AUTHOR]

Breeding for nitrogen use efficiency (NUE) is important to deal with food insecurity and its effect on grain quality, particularly protein. A total of 1679 hybrids were evaluated in 16 different trials for grain yield (GY), grain quality traits (protein, starch and oil content) and kernel weight (KW) under optimum and managed low soil nitrogen fields in Kiboko, Kenya, from 2011 to 2014. The objectives of our study were to understand (i) the effect of low soil N stress on GY and quality traits, (ii) the relationship between GY and quality traits under each soil management condition and (iii) the relationship of traits with low-N versus optimum conditions. From the results, we observed the negative effects of low N on GY, KW and the percentage of protein content, and a positive effect on the percentage of starch content. The correlation between GY and all quality traits was very weak under both soil N conditions. GY had a strong relationship with KW under both optimum and low soil N conditions. Protein and starch content was significantly negative under both optimum and low-N conditions. There was no clear relationship among quality traits under optimum and low N, except for oil content. Therefore, it seems feasible to simultaneously improve GY along with quality traits under both optimum and low-N conditions, except for oil content. However, the negative trend observed between GY (starch) and protein content suggests the need for the regular monitoring of protein and starch content to identify varieties that combine both high GY and acceptable quality. Finally, we recommend further research with a few tropical maize genotypes contrasting for NUE to understand the relationship between the change in grain quality and NUE under low-N conditions. [ABSTRACT FROM AUTHOR]

The absence of genetic variability among crop genotypes is an impediment to breeding progress, hence mutagenesis could serve as a useful tool to create genetic variation to obtain desirable traits of interest. In this study, four maize genotypes, Obatampa, Dapango, Pann 54 and Honampa which were susceptible to maize streak disease (MSD) were acutely irradiated at 254.3 Gy, using a cobalt 60 (60Co) at a rate of 300 Gy/hr. The irradiated seeds were planted with their parental controls at streak disease highly endemic environment. Field trials for the selected maize genotypes were conducted from the M 1 to M 4 generations to screen for MSD resistance and improved grain yield. Sixteen putative mutants and four individual parental controls were selected across the four maize genotypes at the end of the M 4 generation based on disease severity score and yield indices. Detailed morphological screening and field evaluation of putative mutants showing improved plant architecture, increased grain yield and resistance to maize streak disease were tagged and selected. Obatanpa-induced-genotype was the best mutant identified with a grain yield of 6.8 t ha−1. Data on days to 50% flowering indicated that all 16 putative mutants were maturing plants. • Four maize genotypes susceptible to maize streak were irradiated at 254.3 Gy. • 16 mutants were selected at M 4 generation based for on disease severity and yield. • The mutants showed increased grain yield and resistance to maize streak disease. • Obatanpa-induced-genotype was the best with a grain yield of 6.8 t ha−1 [ABSTRACT FROM AUTHOR]