Lolium perenne L. (perennial ryegrass) shows variable levels of seed physiological dormancy (PD), which depends on the genotype and environmental condition during seed development. To analyse the effect of field temperature and precipitation during seed filling on the PD, two cultivars were sown on five dates in 2014 and 2015. After harvest, the level of seed PD was 4–28%. High-temperature stress (>29°C) in the field during seed development, measured as heat stress units (HSUs), reduced seed PD (increased germination) at harvest. After 9 months of dry afterripening under laboratory conditions, mean dormant seed values were reduced from 15 ± 8 to 8 ± 7%. An increment in the seed PD level reduced seedling emergence in the field. Seed with 20% PD produced only 50% of field emergence, under optimal environmental conditions. Different vigour tests were conducted and each was compared with field emergence. The speed of germination, through the first count at 5 d of the standard germination test, and the shoot length at 10 d were better associated with the seedling establishment in the field. The HSU could be useful to establish a possible PD range in the seed of perennial ryegrass after the growing season. The development of models considering the HSU and other climatic parameters could motivate future studies.

The field emergence ability of a total of 88 seed lots of spring barley (Hordeum vulgare L.) harvested serially during development in 2 years was compared, as was the size of the resultant seedlings. For seedsproduced in each year, field emergence and the mean dry weight of emerged seedlings were significantly greater for seed lots harvested some timeafter physiological maturity (end of the seed-filling period) than for those harvested at or before this developmental stage. This is compatiblewith results for the potential longevity of these lots. It is concluded that barley seed quality continues to increase after physiological maturity, and that the developing seeds attain maximum quality (however this is assessed) close to when the seed crop can be combine harvested. Positive correlations were detected between seedling emergence and seed dry weight (P<0.05) and between the mean dry weight of emerged seedlings and seed dry weight (P<0.005) among seed lots harvested close to when maximum quality was attained in four seed production environments.