Comparison of colonization among half‐sib families of Medicago sativa L. by Glomus versiforme (Daniels and Trappe) Berch.

SUMMARY Twenty half‐sib families from within each of two populations of Medicago sativa L. (Pioneer 530 and OAC 78–101) were assessed for differences in ability to form vesicular‐arbuscular mycorrhizas (VAM) when grown in association with one VAM fungal species, Glomus versiforme (Daniels and Trappe) Berch. The families were grown under controlled environmental conditions using a culture‐pot system. Roots were cleared, stained and assessed for percent colonization. From the analyses of variance, the genetic variance and heritability of percent colonization were estimated. The mean percent colonization was 5.8 and 6.8% for the Pioneer 530 and OAC 78–101 populations, respectively. Significant (P < 0·05) differences in percent colonization were detected among half‐sib families derived from Pioneer 530 but not among half‐sib families derived from OAC 78–101. Significant (P < 0·05) pot and run effects were detected in the latter experiment which may have masked differences among the families. The estimate of narrow‐sense heritability of percent colonization in the Pioneer 530 population was 18·8% and the expected response to selection for percent colonization, if the top 10% of the population was selected, was 2·2% per cycle. This indicated that there was good potential for improving the extent of VAM colonization in the population of alfalfa. Further studies of host genotype‐VAM symbioses are warranted.