Genetic and biochemical characterization of parental inbred lines in marker assisted selection for quality protein maize

Abstract

Maize protein is deficient in two essential amino acids, lysine and tryptophan. Naturally occurring opaque2 (o2) mutation which increases the levels of tryptophan and lysine in the grain also confers an undesirable phenotype leading to low yields and more susceptible, soft and chalky kernels. Quality Protein Maize (QPM) is agronomically acceptable and nutritionally improved opaque2 maize. Marker assisted selection increases reliability and efficiency, reduces time and costs taken to obtain QPM. The results presented in this paper are a part of the Maize Research Insitute project on conversion of normal maize lines to QPM lines adapted for growing in temperate regions trough marker assisted backcross (MAB). Genetic and biochemical variability was analyzed between normal (ZPL 5) and QPM (CML 144) parental inbred lines and the efficiency of the three opaque2 specific SSR markers was examined. Markers phi057 and umc1066 can discriminate homozygous and heterozygous backcross progeny, thus can be used as foreground selection markers for the opaque2 gene. The genetic similarity between analyzed lines was 0.05, which confirmed good selection of parental lines for the creation of hybrids. Tryptophan content was 0.093 and QI was 0.85 in CML 144, approximately twice as high compared to 0.054 and 0.48 in ZPL 5. Both tryptophan and QI values for CML 144 were above the QPM treshold, i.e. tryptophan for 24% and QI for 0.625%, making it a suitable donor line of o2. These results represent the framework for marker assisted introgression of the quality protein trait into local maize genotype.