Seed maturity in four cool-season forage grasses

Excessive seed shattering of perennial grasses in the Triticeae tribe results in major economic losses to seed producers, In this 4-yr field study, heat units expressed as growing degree-days (GDD) after anthesis were related to seed development in tetraploid crested wheatgrass [Agropyron desertonrm (Fisch, ex Link) Schultes], Russian wildrye [Psathyrostachys juncea (Fisch,) Nevski], intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw, & D.R. Dewey], and western wheatgrass [Pascopyrum smithii (Rydb,) A, Love]. Seed quality at different stages of development was assessed by germination percentage and emergence of seedlings from a 5.0-cm planting depth in a Parshall fine sandy loam soil (coarse-loamy, mixed Pachic Haploborolls), Water concentration of the seed at maximum seed mass (dry wt, basis) ranged from 303 g kg(-1) for intermediate wheatgrass to 376 g kg(-1) for western wheatgrass. Seed mass was closely associated with seed vigor in all four grass species, as evidenced by correlation coefficients between seed mass and seedling emergence of 0.88** for crested wheatgrass, 0.93** for Russian wildrye, 0.92** for intermediate wheatgrass, and 0.77** for western wheatgrass, Plots sampled at the stiff dough stage had a water concentration of approximately 350 g kg(-1) (dry wt, basis), and the seed sample was at or near maximum seed mass. Seed mass and germination would not be seriously compromised and seed yield losses from shattering would be reduced if windrowing were completed about 50 GDD or 2 to 3 calendar days before maximum seed mass is attained.