Monday, November 13, 2006

Potential use of fresh weight yield as an indirect selection method for dry matter yield in Lolium perenne L.

Patrick Conaghan1, Michael Casler2, Padraig O'Kiely1, and Leslie Dowley1. (1) Teagasc, Oak Park Research Centre, Carlow, Ireland, (2) USDA-ARS U.S. Dairy Forage Res.Ctr., 1925 Linden Drive West, Madison, WI 53706-1108

Dry matter yield (DMY) is a high-priority trait in breeding perennial forage grasses. Selection for increased DMY involves some form of family selection across replicated plots. Sampling plots for dry matter determination is highly labor intensive, particularly for multiple cuttings within a season. Indirect selection on fresh weight yield (FWY) would be easier, quicker and less expensive to evaluate, allowing a greater number of genotypes/environments/replicates to be assessed. Over a 10-yr period, monoculture swards (6 m x 1.5 m) of Lolium perenne L. sown at Oak Park Research Centre were each assessed for DMY and FWY at each cut over a 2-yr period. Two management regimes were imposed: simulated grazing (eight cuts/yr) and conservation (four cuts/yr). Each regime consisted of 150 trials (mean 20.7 families/trial) arranged in a randomized complete block design with two replicates. With few exceptions, the phenotypic correlation coefficient between DMY and FWY was positive. Correlations for annual yield averaged across both evaluation years of the simulated grazing and conservation regimes were 0.84+/-0.01 (simulated grazing) and 0.78+/-0.01 (conservation) and at least 0.84+/-0.01(simulated grazing) and 0.72+/-0.02 (conservation) for each harvest. The top 5 genotypes with the highest annual DMY within each trial, based on means over 2 blocks, were defined as the “correct” selections. On this basis, the number of “correct” selections at each cut based on FWY averaged 3.9 and 3.4 for the simulated grazing and conservation regimes, respectively. Corresponding numbers of “correct” selections for mean annual yield were 3.5 and 3.3. These findings suggest that FWY offers an effective indirect selection criterion for DMY in breeding perennial ryegrass populations within a relatively narrow maturity range.