Evaluating pasture forage plant breeding achievements: A review

Forage plant breeding aims to deliver cultivars that increase on-farm productivity through improved seasonal and annual yield, persistence of yield in perennials, and nutritive and feeding value. Breeding is generally undertaken in highly controlled field trials with individual plants or rows. However, the correlation of trait values between spaced plant trials and sward plots of forages is often low and non-significant. Heritability of traits, a measure of likely gains that can be achieved from plant breeding, can be moderate to high for many traits. The upper level of genetic gains in forage yield measured in small plot trials ranges between 6% and 15% per decade depending on species, indicating significant and lasting improvements have been achieved. Results from some farmlet scale grazing trials measuring animal performance support this but some others, particularly with dairy cows, fail to show advantage to improved cultivars. Factors contributing to this include aspects of systems management, systems trial design, and/or breeding objectives and evaluation systems; occurrence of environmental stresses; insufficient statistical power; and scaling interactions that restrict or dilute trait expression. Several factors are identified that should be considered as evaluation systems evolve in response to the changing economic, climatic, and regulatory forces affecting grassland farming.