837 PB 355 A COMPARISON OF BROCCOLI SEED PRIMING TREATMENTS

Abstract

Various osmotic solutions and solid carriers have been used to prime (controlled hydration followed by drying) seeds. Broccoli (Brassica oleracea L., var. italica, cvs. Brigadier and Earlidawn) seeds were primed in solutions of polyethylene glycol, potassium nitrate (KNO3), and mannitol or calcium silicate (Micro-ccl E) and vermiculite to determine which treatment provided the greatest enhancement of germination. Germination percentage and rate as well as head yield were determined in a series of laboratory, glasshouse, and field experiments over a three year period. Water potentials (Y) ranged from -0.8 to -2.6 MPa at 20°C for both osmotic solutions and carriers. The duration of the priming treatments were 3, 7, or 10 days. All priming treatments, except KNO3 and mannitol, consistently reduced the mean time to germination in the laboratory, reduced the mean time to field emergence, increased final stands, but did not affect the mean time to harvest. However, solid phase was more effective than osmotic priming at each Ψ tested. The best solid priming mixture was 1.0:0.8:1.8 (seed:carrier:water) for 7 days at 20°C using Micro-cel E. This treatment was measured to have a Y = -1.2 MPa, and other types of priming at the same Y were less effective. The Y threshold below which no priming effect was obtained was Ψ= -2.4 MPa. Priming response was closely associated with, but not entirely dependent on, the Ψ of the treatment.