Genetic characterization of pro-vitamin A and quality protein maize inbred lines and their derived hybrids.

Abstract

Maize is one of the most important crop plant, valued both as cereal and forage crop because of high nutrition and palatability. Sub-Saharan Africa (SSA) countries are highly dependent on maize compared to other African countries and there is preference of white maize over orange maize, which leads to Vitamin A deficiency (VAD) crisis. Vitamin A deficiency can be alleviated by increasing pro-Vitamin A maize consumption rate in the population. In orange maize, Vitamin A is in the form of pro-Vitamin A, therefore crops with high content of pro-Vitamin A carotenoids are a promising strategy to alleviate Vitamin A content among disadvantaged populations. Lack of quality proteins in maize is another challenge faced the consumers of this staple crop in SSA. Therefore maize requires improvement in this regard. Quality protein maize (QPM) was developed from mutant maize with an opaque- 2 gene that improves amino acids; lysine and tryptophan. Lysine and tryptophan allow the body to manufacture complete proteins, and tryptophan lessens the prevalence of kwashiorkor in children. Studies clearly show that QPM could be superior to normal maize (NM) if used in the diet of humans. The objectives of this study were therefore to analyze the genetic diversity among the Pro-Vitamin A lines, Quality Protein Maize lines, and Normal Maize lines; to identify potential heterotic groups, and to evaluate their F1 hybrids. Twenty maize inbred lines were used in the study, comprising 13 Pro-Vitamin A; four QPM and three normal lines. The lines were genotyped with 93 SNP markers at the DNA Landmarks Laboratory in Canada. Data was analyzed using the PowerMarker version 3.25 statistical package. The hybrids were generated in a 4 X 10 North Carolina design II with reciprocal mating which resulted in 78 experimental hybrids with adequate seed for planting in trials. Three commercial hybrids were included as controls. The 81 hybrids was evaluated in a 9 x 9 alpha-lattice design with two replications at four sites in KwaZulu-Natal, South Africa. The data collected was analyzed using Genstat. Out of 93 SNPs markers used, six of them were monomorphic and 87 polymorphic. The use of SNP markers was effective; the data set reflected the homogenously homozygous state of inbred lines and was able to determine the genetic diversity and distance. Inbred lines that showed the highest genetic distance were normal maize (DPVA17) and pro-Vitamin A (DPVA12) which was 0.54; and lowest genetic distance was observed between normal maize (DPVA19) and normal maize (DPVA18) which was 0.11. In the current study the higher genetic diversity was observed between previously identified groups and six potential heterotic groups were identified. Grain yield of the hybrids was highly significant at Cedara and Dundee, and not significant at Jozini and Ukulinga. The three economic traits (ear aspect, number of ears per plant, and grain moisture content) were significant at all sites. Genotype x environment interaction effects were observed. Performance of hybrids varied with sites. At Cedara, the highest performing experimental hybrid was 14PVAH-29, Dundee; 14PVAH-166, Jozini; 14PVAH-8, and Ukulinga; 14PVAH-50, respectively. Hybrid 14PVAH-139, 14PVAH-129, 14PVAH-149, and 14PVAH-10 were placed by three methods in top 10% stable hybrids, thus they are considered as the most stable hybrids. The current study showed that traits such as number of ears per plant, plant height, and ear aspect are strongly associated positively with yield, and that stem lodging, root lodging, and ear rot are negatively associated to yield. Although DNA molecular markers can be used in identifying heterotic groups, the relationship of genetic distance and hybrid vigour is still not well understood. Therefore, both molecular markers and conventional field trials (phenotyping) must be used to identify heterotic groups among pro-Vitamin A and quality protein maize. This would be crucial for devising breeding strategies for developing nutritionally rich maize hybrids.