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Two Cycles of Directional Selection for Improved Nutritive Value of Alfalfa¹

A 6-hour in vitro dry matter disappearance (GH-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 GH-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 GH-DMD values were higher in leaf content but lower in NDF content than progeny from clones with low GH-DMD values. Comparisons of selected two-clone combinations in the first and second cycles indicated second cycle selection was effective in separating progeny means.

Key Words: Forage quality • Neutral detergent fiber • Medicago glutinosa M.B.

² Formerly, NDEA Fellow at Michigan State University (now Assistant Professor of Agronomy at The Pennsylvania State University, University Park, Pennsylvania) and Professor, Department of Crop and Soil Sciences, Michigan State University, East Lansing, Michigan.

Received for publication June 13, 1970.

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