Flowering of Berseem Clover Types in Response to Vernalization

Winter hardiness of ‘Bigbee’ berseem clover ( Trifolium alexandrinum L.) was reported to differ between plants grown from certified seed and breeder seed. Winter growth form also differed, with plants from breeder seed forming a rosette and plants from certified seed elongating. To determine if growth form differences were due to a change in vernalization response, imbibed seeds of Bigbee certified and breeder seed and certified ‘Multicut’ were vernalized at 2°C for 0 to 6 wk in weekly increments. Seeds from all treatments were simultaneously germinated and grown in a greenhouse under 18‐h daylength. Days to flowering, node at first flower, and the number of nodes below 5 cm at flowering were recorded. Replicated experiments were conducted with germination dates of 17 Aug. 1992 and 25 Feb. 1993. The regression of days to flowering and node at first flower on vernalization period was significant for Bigbee certified and breeder seed. Response slopes of Bigbee plants grown from certified and breeder seed differed from each other for all variables. As vernalization period decreased, plants from Bigbee breeder seed flowered later and at a higher node than plants from Bigbee certified seed. Vernalization had no effect on days to flowering or node at first flower for Multicut. Variation in vernalization response between Bigbee breeder seed and certified seed indicated that a change occurred during the production of certified seed. Multicut and Bigbee certified seed may have less winter grazing tolerance than Bigbee breeder seed since there were fewer nodes near the soil line to support regrowth.