Genetic variation and response to selection for legume-compatibility traits in orchardgrass
Perennial grass-legume mixtures are important in forage production; however, little effort has been devoted to breeding either the grass or legume component for increased compatibility in mixtures. The objectives of this research were to study the genetic variation and response to selection for legume-compatibility traits in orchardgrass. Individual plants in 97 different germplasms were evaluated for vigor traits, canopy height, growth habit, anthesis date, tiller number and leaf length and width. Polycross progenies of the parents of Iowa 79-OGP-DT were chosen for more detailed study because of their superiority in rust resistance, vigor, and winterhardiness and their variability for traits that may affect compatibility with a legume. Individual plant heritabilities were greater than 0.40 for spring canopy height, growth habit, anthesis date, and leaf width. Significant phenotype correlations indicated that winterhardiness, vigorous growth, tall spring canopy height, erect growth habit, early anthesis, and narrow leaves tend to be associated with each other. High tiller number was associated with superior spring and fall vigor, and relatively high winterhardiness. Six cycle-1 populations were developed by divergent selection in the polycross progenies for maturity, spring canopy height, and a compatibility index incorporating spring vigor, spring canopy height, growth habit, and tiller number. Significant direct and correlated responses were obtained from each selection strategy. Selection for early maturity, tall canopy height, and a high compatibility index value always decreased days to anthesis and increased spring canopy height, erectness of growth, tiller number, and dry matter yield in a space-planted test with the converse occurring from selection in the opposite direction. The three populations derived from selection for a high compatibility index value, tall spring canopy height, and early maturity consistently yielded more forage than their respective divergent populations in a space-planted test, in dense monoculture stands, and in mixtures with birdsfoot trefoil. The less aggressive populations permitted significantly more birdsfoot trefoil production in mixtures than the aggressive populations. This research indicates that it is possible to increase the compatibility of orchardgrass with birdsfoot trefoil by selection among spaced plants for decreased spring canopy height, decreased tiller number, and delayed maturity.