Genetic enhancement of early and extra-early maturing maize for tolerance to low-soil nitrogen in sub-Saharan Africa

Open Access ArticleTo increase and improve food crop production and crop management for sustainable agricultural development, the Maize Improvement Program (MIP) of the International Institute of Tropical Agriculture (IITA) has, in partnership with national and international organizations, focused attention on the genetic improvement of maize (Zea mays L.) for tolerance/resistance to abiotic and biotic stresses constraining maize grain production. One of the abiotic stresses into which new technologies have been established for crop protection and sustainable natural resource management is low soil nitrogen (N). Nitrogen, an important plant nutrient required for growth and productivity, is not readily available and little quantity or none is applied by farmers for maize production. Because of long periods of bush fallow, the absence of N was not noticeable at the initial stages of maize production in West and Central Africa (WCA). However, with the fallow period gradually reducing and totally disappearing, it has become imperative for external supply of N in maize production. Taking a cue from the International Maize and Wheat Improvement Centre (CIMMYT), IITA has been breeding low-N tolerant maize and several low-N-tolerant maize varieties and hybrids are now available to farmers. Reviewed in this manuscript are the efforts used to develop low-N tolerant early and extra-early maturing maize by the MIP of IITA. The review covers the objectives, methodology, and output of the research, including the genetics of tolerance, ongoing conventional and molecular approaches, and the gaps that new research could fill

Genome-wide association analysis reveals genetic architecture and candidate genes associated with grain yield and other traits under low soil nitrogen in early-maturing white quality protein maize inbred lines

Open Access Journal; Published online: 05 May 2022Maize production in the savannas of sub-Saharan Africa (SSA) is constrained by the low nitrogen in the soils. The identification of quantitative trait loci (QTL) conferring tolerance to low soil nitrogen (low-N) is crucial for the successful breeding of high-yielding QPM maize genotypes under low-N conditions. The objective of this study was to identify QTLs significantly associated with grain yield and other low-N tolerance-related traits under low-N. The phenotypic data of 140 early-maturing white quality protein maize (QPM) inbred lines were evaluated under low-N. The inbred lines were genotyped using 49,185 DArTseq markers, from which 7599 markers were filtered for population structure analysis and genome-wide association study (GWAS). The inbred lines were grouped into two major clusters based on the population structure analysis. The GWAS identified 24, 3, 10, and 3 significant SNPs respectively associated with grain yield, stay-green characteristic, and plant and ear aspects, under low-N. Sixteen SNP markers were physically located in proximity to 32 putative genes associated with grain yield, stay-green characteristic, and plant and ear aspects. The putative genes GRMZM2G127139, GRMZM5G848945, GRMZM2G031331, GRMZM2G003493, GRMZM2G067964, GRMZM2G180254, on chromosomes 1, 2, 8, and 10 were involved in cellular nitrogen assimilation and biosynthesis, normal plant growth and development, nitrogen assimilation, and disease resistance. Following the validation of the markers, the putative candidate genes and SNPs could be used as genomic markers for marker-assisted selection, to facilitate genetic gains for low-N tolerance in maize production