Genetic purity and patterns of relationships among tropical highland adapted quality protein and normal maize inbred lines using microsatellite markers

Abstract

Conversion of normal maize (Zea mays L.) into quality protein maize (QPM) significantly improves its nutritional value for humans and animals. Highland adapted normal maize inbred lines were backcrossed with selected QPM donor lines to incorporate the opaque-2 gene. The objectives of this study were to verify the genetic purity, determine the effect of conversion of normal maize lines to QPM and understand patterns of relationships among 36 white maize inbred lines (30 QPM and 6 non-QPM) using 25 simple sequence repeat (SSR) markers. The proportion of observed heterozygosity within an inbred line varied from 4 to 16.7 % and the average was 7.9 %. Twenty of the 36 inbred lines (55.6 %) showed higher than the expected 6.25 % mean residual heterozygosity for inbred lines developed after four generations of selfing. The genetic distances between pair-wise comparisons of the 36 inbred lines ranged from 0.077 to 0.780 and the average was 0.52. Nearly 98 % of the pair-wise comparisons had a distance between 0.30 and 0.78, which indicates large genetic differences among most lines. The model-based population structure, principal coordinate and neighbor-joining cluster analyses revealed the presence of two to three groups, which is generally consistent with pedigree information and partly with heterotic grouping. Analysis of molecular variance indicated that difference among heterotic groups explained 8.6 to 15.4 % of the total SSR variance, indicating the presence of moderate to great genetic differentiation among heterotic groups.