Alfalfa forage yield and leaf/stem ratio: narrow-sense heritability, genetic correlation, and parent selection procedures

Abstract

Forage yield, and forage quality as inferred by high leaf/stem ratio, are pivotal alfalfa breeding targets. However, information on narrow-sense heritability ( $$h_{N}^{2}$$ ) and genetic correlation (r g ) of these traits is scant and mostly inferred from limited germplasm samples and trait observation. This study aimed at: (i) generating $$h_{N}^{2}$$ , r g and complementary information based on 125 parent genotypes representative of Italian germplasm evaluated as clones, half-sib progenies and selfed (S1) progenies for dry-matter yield over 12 harvests and leaf/stem ratio across two harvests; (ii) assessing the consistency of parent value across evaluation procedures; (iii) verifying leaf/stem ratio changes in two genetic bases selected for higher forage yield. Seeds per tripped flower of selfed parents ranged from 0.16 to 2.53, with high broad-sense heritability on a genotype mean basis ( $$h_{B}^{2}$$ = 0.81). Genotype cloning success across three experiments displayed moderate $$h_{B}^{2}$$ (0.44). Forage yield exhibited large genetic variation but fairly modest $$h_{N}^{2}$$ (0.21), whereas leaf/stem ratio featured high $$h_{N}^{2}$$ (0.75). Inbreeding depression for yield averaged 39 %. Non-additive genetic effects were almost as large as additive ones for DM yield, and extremely low for leaf/stem ratio. Additive genetic effects had greater impact than inbreeding depression on parent yielding ability based on S1 progenies. Forage yield and leaf/stem ratio were independent according to genetic correlations for parent-offspring (r g = −0.18) and half-sib progeny data (r g = −0.33) and the lack of leaf/stem ratio change in material selected for higher yield. Forage yield can profit of genotypic selection, whereas phenotypic selection on large plant numbers is preferable for leaf/stem ratio.