The development of seed quality in spring barley in four environments. I. Germination and longevity

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Abstract
Seed development and changes in germination ability and longevity were monitored in control and shaded spring barley (Hordeum vulgareL.)crops grown in two contrasting years. Shading reduced seed dry matter accumulation rates by 24–28% and delayed maturation drying slightly, but had little effect (0–2 d) on the timing of physiological maturity (end of the seed-filling period); final seed dry weights were 76–85% of controls. Moisture contents (wb) at physiological maturity were 48–55%; final mean seed dry weights in the controls were 40.9 mg(S.E. 0.6) in 1988 and 35.2 mg (S.E. 0.5) in 1989. Shading had little orno effect on germination ability or longevity in either year. Seeds fromthe first harvest were viable when dried below 15% moisture content despite being only 34% (1988) to 63% (1989) filled; desiccation promoted germination. Maximum germination achieved after forced desiccation occurredin seeds harvested 7–10 d (1989) to 11–13 d (1988) after physiological maturity, with little subsequent change during the following 14 (1988) or 27 d (1989). Longevity continued to increase during development until a maximum was reached 18–20 d (1988) to 27 d (1989) after physiological maturity (at moisture contents on the mother plant of 18–19% and 14–15%, respectively). In both years, the longevity of these seeds was greater (P<0.005) than that of seeds harvested either subsequently or earlier at physiological maturity. The results contradict the hypothesis that maximum seed quality coincides with physiological maturity and thereafter declines. Rather, maximum seed quality was attained close to when barley seed crops can be combine harvested The subsequent decline in potential longevity on the maternal plant in the field was quantitatively similar to that expected during post-harvest storage.