Population improvement in lucerne (Medicago sativa L.): genetic analyses in original and improved populations

Abstract

Most quantitative genetics analyses are limited to the first (mean) and second (variance) degree statistics and their derivatives. Analyses based on third (skewness) and fourth (kurtosis) degree statistics can be useful especially for detecting and characterising the nature of gene interactions. Third and fourth degree statistics were analysed and used to interpret differences in forage yield among S₁ families of lucerne derived from double-cross populations that were synthesised before (OGDC) and after (AGDC) improvement via inbreeding and selection. Higher levels of genetic load (deleterious alleles) were revealed in the OGDC population compared with the improved population. The analyses also revealed the importance of gene interaction for forage yield in lucerne. In the unselected OGDC population, interaction between alleles in repulsion phase linkages was more important, whereas, in the selected AGDC population, interaction between alleles linked in coupling phase assumed greater importance. The above results suggest that inbreeding and selection in lucerne can accumulate favourable alleles over generations of selection and result in population improvement. Skewness and kurtosis are relatively easy to compute and interpret and should serve as valuable tools in tetraploid quantitative genetics analyses.