Genetic variation and selection for shoot and rhizome growth traits in a naturalized quackgrass population

Quackgrass [Elytrigia repens (L.) Nevski; Agropyron repens (L.) Beauv.; Ely mus repens (L.) Gould] is a perennial grass that has colonized much of the world's temperate cropland. Its persistence, perenniality, high nutritional value, and tolerance to several stress factors make it a potentially usefu l forage crop. This research was undertaken to assess the breeding improvem ent potential of quackgrass for direct use as a forage crop. Thirty-five qu ackgrass parent clones were grown in a series of four greenhouse experiment s (growth periods) between November 1981 and March 1984, and in a field exp eriment from July 1984 to June 1985. A random sample of their polycross pro geny was grown in a field experiment from September 1982 to June 1984. Pare nt means, family means, and progeny means within families varied (P < 0.01) for all traits determined. Greenhouse traits had moderate repeatability (0 .50-0.72), high clone X growth period interaction, and low correlation coef ficients with field traits (r = -0.50-0.32). Thus, selection should be cond ucted in the field. There were large amounts of additive genetic variation for all three field traits (forage yield, plant diameter, and maturity). Re alized gains from one cycle of selection were between expected gains for di somic and tetrasomic inheritance models. Late maturity was associated with low plant diameter during selection. Forage yield responded to selection, b ut appeared to be governed primarily by inbreeding because of small effecti ve population sizes. Quackgrass plants that thrive in pastures and cropland s still contain hidden alleles for low-rhizome-spreading phenotypes.