Search

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]

Abstract: Quality protein maize (QPM) breeding involves the combined use of the opaque-2 (o2) gene and the genetic modifiers of the o2 locus to develop cultivars with modified kernel endosperm, and increased concentrations of lysine and tryptophan. This study was designed to assess grain yield performance, endosperm modification, and protein quality and quantity under two contrasting soil nitrogen environments. A 15-parent diallel cross was evaluated under one low nitrogen stress and one optimal nitrogen environment each at Harare (Zimbabwe) and Bako (Ethiopia). Most QPM hybrids showed higher protein quality levels than the best non-QPM check under both conditions. Protein concentration tended to vary across nitrogen levels, but not endosperm type. Significant differences were found for the test of main effect (nitrogen-level) for endosperm modification and tryptophan concentration. This indicated that QPM maintains quality even under low soil nitrogen, a widespread condition in Africa. General combining ability (GCA) mean squares were highly significant for most protein quality traits for each environment and across environments whereas specific combining ability (SCA) mean squares were not significant in most cases. This indicated that additive gene effects were primarily responsible for variation of most traits evaluated and hence progeny performance can adequately be predicted on the basis of parental performance. Inbred lines P2, P4 and P12 had desirable GCA effects for endosperm modification while P1 and P3 had the best GCA for tryptophan concentration in grain. The current study suggests that hybrids with desirable endosperm modification, protein quality and stable performance under low nitrogen stress and optimal conditions can be produced with careful selection. [Copyright &y& Elsevier]

Information on heterotic patterns of quality protein maize (QPM) inbred lines would help to design appropriate breeding strategies for QPM. The objectives of this study were to assess the genetic relationships and heterotic structure of elite QPM inbred lines adapted to eastern and southern Africa (ESA) using simple sequence repeat (SSR) markers. Thirty-five inbred lines consisting of 32 QPM and three non-QPM inbred lines were genotyped using 40 SSR markers that yielded a total of 217 alleles, with an average of 5.43 and range of 2-10 alleles per marker. The number of alleles per inbred line varied from 40 to 82, with a mean of 51.5. About 81% of the pairwise comparisons between the lines had genetic distance estimates varying from 0.250 to 0.415. The unweighted paired group method using arithmetic averages (UPGMA) clustering algorithm and model-based population structure analysis showed the presence of two to three major groups, mainly consistent with maturity groups and pedigree information. This information can facilitate effective utilization of the QPM inbred lines in breeding programs. [ABSTRACT FROM AUTHOR]