A low-cost procedure for multi-purpose,large-scale field evaluation of forage crop genetic resources

The proposed procedure for field evaluation of large forage germplasm collections allows for simultaneously performing germplasm characterization, stratified mass selection and the assessment of the genetic structure of populations as revealed by among-population vs. within-population genetic variances. Unreplicated genotypes are randomly assigned to different units (grids) with the constraint that each unit should have a fixed proportion of genotypes from each population. The relative homogeneity of plant material between units allows for investigating major spatial trends.Within each unit, one plant is actually a clonal control allocated randomly and used for estimating the environmental variance. The units have a square shape, with plants grown in dense planting arranged at same spacing between and within rows. A set of adjacent units forms a column, and several parallel columns may exist. Observed data can be adjusted for the effects of: i) column of units; ii) row of units (by covariance analysis, using row number as the covariate); and iii) column of plants within units. The procedure was applied to the evaluation of 4,480 lucerne genotypes subdivided into 128 units and grown at 10 cm spacing. The efficiency of data adjustment, estimated as the variance among clones for unadjusted data relative to that for adjusted data, was 33.7% for length of the main stem, 9.8% for plant dry weight, and greater than 7% for three out of four other evaluated traits.