| Summary: | High quality seed is essential for the establishment of a good crop. New Zealand grown brassica seeds usually have high germination but often have variable seed vigour. The latter can result in poor crop establishment and storability. High temperature stress during seed development is known to reduce seed vigour in some species, but whether temperature stress is responsible for seed vigour loss in brassica species was not known. The effects of high temperature during seed development on forage rape (Brassica napus) seed quality were determined by assessing seed mass, germination and vigour using a sowing date trial and field and controlled environment experiments. A time of sowing trial was conducted in the 2011-12 season. A late flowering forage rape cultivar “Greenland” was sown on 25 March and 13 April, 2011 with sowings replicated four times in a randomized complete block design. Seed quality was assessed at three seed development stages (determined by seed moisture content (SMC)): at physiological maturity (PM) (≈50% SMC), pre-desiccation final stage (≈25% SMC) and harvest maturity (≈14% SMC). Seed had attained PM at between 47-52% SMC which was similar to other brassica species. The seed quality testing results demonstrated that sowing time had no effect on seed germination in the prevailing environmental conditions in that season, and at PM there were no differences in seed vigour. However, seed vigour was significantly reduced in seeds harvested at the pre-desiccation (≈25% SMC) and harvest maturity (HM) (≈14% SMC) stages for the early sowing. This was explained by a longer time of exposure to conditions which caused weathering during maturation for the March sowing. In a controlled growth room, set at 30/25 ˚C (day/night, 12 hours each, R.H 70%), plants received heat stress for four days (240 ˚Ch) at (i) seed filling ii) PM and iii) seed filling plus PM before being returned to the field until seed harvest for two consecutive seasons, 2011-12 and 2012-13. Heat stress decreased seed quality in all three ...
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