Environmental Control of Floral Induction and Development in Kentucky Bluegrass

Kentucky bluegrass (Poa pratensis L.) floral induction requires a lengthy, uninterrupted period of cold temperature with a short photoperiod. Our objective was to develop an deficient artificial vernalization procedure to facilitate breeding experiments. The stage of plant development and length of vernalization period necessary for floral induction was determined for six cultivars: Abbey, Aspen, Midnight, Park, Rugby, and Trenton. Plants were exposed progressively to three temperature and light-controlled environments: (i) seedlings were grown in a 12-h photo- and thermal period with a 20°C day/14°C night temperature regime and high irradiance of 30 W m⁻² from germination until 3, 5, 9, or 13 wk after emergence (approx. 8, 26, 145, and 198 leaf stage, respectively); (ii) plants were then vernalized for an 8-h photoperiod at 5°C constant temperature and low irradiance of 7 W-2 for 4, 8, or 12 wks; and (iii) plants were transferred panicle development conditions of 18-h photoperiod and 12-h thermal period with a 18°C day/15°C night temperature regime and high irradiance of 30 W⁻¹ for 16 wk. No panicles were observed on plants with the 4-wk vernalization treatment. For all cultivars except Midnight, the 9-wk plant development and 12-wk vernalization treatment resulted in floral induction of all plants. The same four cultivars responded to this treatment with a mean panicle number greater than five panicles per plant and the time from seedling emergence to 75% of the panicles emerged was approximately 28 wk. This study has demonstrated that an artificial vernalization procedure could be developed that would make reproductive material of Kentucky bluegrass available throughout the year independent of season or climate. Contribution of the Minnesota Agric. Exp. Stn., J. Paper no. 21,636.