Effect of Plant Growth Regulator and Irrigation on Physiological and Harvest Maturity in Relation to Seed Quality of Red Clover.

Red clover is widely grown as a seed crop in western Oregon. Seed yield is affected by plant growth regulator and irrigation; however, the effect of these factors on physiological (PM), harvest maturity (HM), and seed quality is unknown. This study was conducted to determine the effect of trinexapac-ethyl (TE) plant growth regulator and irrigation on PM (maximum seed dry weight), HM (at direct combine), and seed viability and vigor of red clover at different stages of maturity. Five TE rates ranging between 0-700 g a.i. ha^-1 were sprayed at stem elongation and bud formation growth stages. Irrigation was applied at the flower development stage. Seeds were sampled twice each week after anthesis until harvest. Physiological and visual indicators of seed maturity were collected to determine the PM and the HM. Germination, tetrazolium (TZ), and cold tests were conducted to evaluate seed viability and vigor at weekly intervals after seed formation. The two-year study indicated that TE applications did not alter seed maturation. The irrigation resulted in a four-day delay in PM compared to the non-irrigated treatment. Red clover from all treatments reached PM when the inflorescence contained light brown petals with dark green sepals and seeds ranged from pale green to pale yellow. Seed dry weight did not change significantly from PM to HM. Seed moisture content at PM ranged from 340 to 540 g kg^-1, and was approximately 100 g kg^-1 at HM. Inflorescences at HM contained dark brown petals and sepals and seeds were yellow or different shades of yellow-purple. Seeds were hard and easy to separate from the inflorescences at HM. Seeds of all treatments had similar qualities at HM, with viability by TZ and germination tests ranging from 93-100% and vigor by the cold test ranging from 92-96%.