Genetic improvement of key agronomic traits in Melilotus albus

Melilotus albus Medik. is a legume species with potential to be used as a forage or conserved fodder in Northwest China. Breeding M. albus as a forage crop is focused on simultaneously improving forage yield and reducing coumarin (Cou) content. The goal of the present study was to estimate genotypic variation for several key agronomic traits and to evaluate the impact of single-trait selection and Smith–Hazel-index-based multitrait selection for herbage dry weight (DW), plant height (PH), stem number (SN), and leaf area (LA). A quantitative genetic analysis was conducted on trait measurements from 25 half-sib (HS) families evaluated at Yuzhong and Linze, in China. Significant (P < 0.05) genotypic variation among the HS families for all traits was observed. There was also significant (P < 0.05) genotype × environment interaction for all traits except for LA. The predicted genetic gain, based on estimated genotypic variance, for single-trait selection varied from 2.3 to 30.3% per selection cycle. Pattern analysis of the HS family × multitrait best linear unbiased prediction matrix provided a graphical summary of the association among the traits, as well as the four HS family groups generated from clustering. Some members within Group 1 could be crossed to generate a breeding population to be used in recurrent selection for M. albus cultivar development in Northwest China. The applicability of a Smith–Hazel selection index to increase expression of the traits DW, PH, and SN and reduce LA, indirectly reducing Cou content, was confirmed. This index enabled identification of families for increasing key biomass traits and decreasing Cou production.