EMERGENCE OF TEMPERATE PASTURE GRASSES FROM DIFFERENT SOWING DEPTHS -IMPORTANCE OF SEED WEIGHT, COLEOPTILE PLUS MESOCOTYL LENGTH AND SHOOTSTRENGTH

Inter-specific relationships between mean seed weight, coleoptile + me socotyl (sub-coleoptile internode) length and width, shoot strength an d emergence from different sowing depths were examined for timothy (Ph leum pratense L., mean seed weight 0.33-0.48 mg depending on seed line ), cocksfoot (Dactylis glomerata L., 0.65-0.78 mg), perennial ryegrass (Lolium perenne L., 1.71-2.19 mg), tall fescue (Festuca arundinacea S chreb., 1.73-2.60 mg), annual ryegrass (Lolium multiflorum Lam., 5.10- 5.20 mg) and prairie grass (Bromus willdenowii Kunth., 10.5-12.2 mg). Across species at 10, 30 and 60 mm sowing depths in the field and 10, 15 and 30 mm sowing depths under controlled environment conditions, th ere was a significant (P < 0.05) positive correlation between emergenc e % and mean seed weight. Across species at 10-30 mm sowing depth unde r controlled environment conditions, emergence % was not significantly correlated with coleoptile + mesocotyl length but there were signific ant positive correlations between emergence % and coleoptile and mesoc otyl width: shoot strength increased with increased coleoptile width a cross species. For seed Lines of timothy of different mean seed weight (0.21-0.81 mg), emergence %, coleoptile + mesocotyl length and coleop tile and mesocotyl width increased with increased seed weight at 10 an d 15 mm sowing depth. Shoot strength increased with increased coleopti le width for timothy. For emerged and non-emerged cocksfoot and timoth y seedlings regardless of seed weight, mean coleoptile + mesocotyl len gth was > 10 mm at 10 mm sowing depth. It is concluded that at 10-30 m m sowing depth, increased emergence % with increased seed weight acros s species is not due to increased coleoptile + mesocotyl length. It is proposed that increased emergence % with increased seed weight across species at 10-30 mm sowing depths and across seed lines of timothy at 10 mm sowing depth is primarily due to increased coleoptile and mesoc otyl width resulting in increased shoot strength and hence an increase d ability to penetrate the substrate.