Two Cycles of Directional Selection for Improved Nutritive Value of Alfalfa¹

Abstract

A 6‐hour in vitro dry matter disappearance (6H‐DMD) procedure was used to evaluate individual progeny of ‘Vernal’ (Medicago sativa L. and Medicago falcata L.) and ‘DuPuits’ (Medicago sativa L.) clones selected for high or low 6H‐DMD values. Progeny derived from clones with high 6H‐DMD values had consistently higher 6H‐DMD values than progeny from low clones. Additional clones of ‘Culver’ MSA‐C4, MSB‐C4, Medicago glutinosa M.B., and Vernal were screened for high or low 6H‐DMD values over two harvests. Selected clones from Vernal and DuPuits progeny and from the five unselected populations were recombined for a second cycle of directional selection.Correlations between yield and 6H‐DMD were negative or near zero. Cell wall analysis of clones selected for a second cycle of improvement indicated a significant positive relationship between total cell wall constituents (NDF) and 6H‐DMD values of the forage.Second cycle clones had significant general and specific combining abilities for yield as well as leaf and NDF content. Progeny from clones with high 6H‐DMD values were higher in leaf content but lower in NDF content than progeny from clones with low 6H‐DMD values. Comparisons of selected two‐clone combinations in the first and second cycles indicated second cycle selection was effective in separating progeny means.

Within‐ and Among‐Cultivar Genetic Variation in Alfalfa: Forage Quality, Morphology, and Yield

“…These differences may then become non‐significant. Shenk and Elliot (1970, 1971) showed the high efficiency of clonal selection on a digestibility trait. However, breeding for feeding value must be accompanied by other traits such as forage yield, seed yield, disease and pest resistances, winter resistance, and fall dormancy.…”

Leaf and stem dry matter digestibility and ruminal undegradable proteins of alfalfa cultivars

“…In our study, Rangelander, Spredor 2, and Heinrichs were the most digestible cultivars with high LWR and a high stem IVDMD, whereas Oneida VR had a low plant IVDMD with a low LWR and stem IVDMD, for both spring growth and summer regrowth. Shenk and Elliott (1970) observed that progeny with high DM digestibility were also higher in leaf content. Alfalfa genotypes with high LWR, TN, and IVDMD improve dairy cow performance (Émile et al 1997).…”

Germplasm Variability and Environmental Effects on Stem Cellulose and Lignin Concentrations in Alfalfa*

“…They concluded that selection for low ADF reduced both total cell wall and ADL concentration. Shenk and Elliot (1970) reported that selection for increased digestibility of the whole herbage decreased cell wall constituents and ADL. Kephart et al.…”

“…They concluded that selection for low ADF reduced both total cell wall and ADL concentration. Shenk and Elliot (1970) reported that selection for increased digestibility of the whole herbage decreased cell wall constituents and ADL. Kephart et al (1989) reported success in selecting for divergent ADL concentration in whole herbage of experimental populations and concluded that many of the differences observed in the divergent ADL lines may have been due to correlated changes in leaf to stem ratio.…”

“…Hill and Barnes (1977) examined the genetic variability for several forage-quality traits for whole herbage in several alfalfa germplasms and found positive correlations between ADF and ADL and negative correlations between CP and either ADF or ADL. Both Shenk and Elliot (1970) and Hill and Barnes (1977) concluded that as no quality parameters were closely correlated with yield, improvement for both yield and quality in alfalfa should be possible.…”