Effects of elevated temperature during grain development of seed quality of barley (Hordeum vulgare L.)
Syankwilimba, Ian S. K.
In order to investigate the effects of elevated temperatures during grain development on seed quality, a series of experiments was carried out using both controlled environment and glasshouse conditions. Plants of several cultivars of barley (Hordeum vulgare L.) were subjected to different temperature regimes during grain development. Temperature treatments ranged from 18°C to 38°C and plants were subjected to elevated temperatures at different stages of grain growth and for different lengths of time. After harvest, the seeds were tested for vigour.Grains which had experienced elevated temperatures for part or all of their developmental period were lighter and had smaller embryos than grains which experienced 18°C for most or all of their developmental period. There was a significant positive correlation between grain dry weight and embryo dry weight. When eleven genotypes were grown in a glasshouse at approximately 18°C/13°C (day/night) and a day length of 18 h, grain dry weight and embryo dry weight varied according to genotype. Genotypes with heavier grains had larger embryos than those with lighter grains.The viability of grains harvested from all temperature regimes was > 94 %. Grains which had experienced elevated temperatures during grain development had a higher percentage germination in tests using 8 ml and 10 ml of water per 100 grains than grains which had experienced 18°C throughout grain development. It was observed that grains harvested from ears grown in elevated temperature regimes had a higher proportion of pre-germinated grains than grains harvested from ears grown at 18°C.Seedlings grown in the dark from grains grown in elevated temperatures had fewer roots, shorter seminal roots and longer plumules than had seedlings from grains which had experienced 18°C throughout development. Root number, length of seminal roots and seedling dry matter showed a strong positive correlation with grain dry weight. There was no statistically significant correlation between plumule length and grain dry weight.When seeds were sown at a depth o f 4 cm in fine sand in pots, seedlings from grains grown at elevated temperatures emerged earlier than those from grains grown at 18°C. However, grains grown at elevated temperatures had a higher proportion of germinated grains whose seedlings failed to emerge to the surface than did grains grown at 18°C.The mean dry weights of the roots and plumules of seedlings from grains grown at 18°C were higher than those of seedlings from grains grown at elevated temperatures. The root dry weight/shoot dry weight ratios (R/S) for seedlings of cultivars normally grown in sub-tropical/tropical climates were lower than those for seedlings of temperate region cultivars, the grains having been grown under the same conditions.Genotypic variations in seedling vigour characteristics were observed in glasshouse- grown material.When grown for five days on 1 % agar, embryos extracted from grains which had been subjected to elevated temperature regimes during grain development produced seedlings with longer plumules and longer roots than did embryos extracted from grains which experienced 18°C throughout development. These differences were not observed when the embryos were grown on an agar/glucose medium.The A-type and B-type starch granules in grains grown in elevated temperature regimes were fewer in number and smaller than those in grains grown at 18°C. Starch from grains which experienced a particular sequence of high temperatures during development had a triphasic size distribution of starch granules.Estimates o f ∝-amylase activity made 48 h after the start of imbibition showed that cc-amylase production was greater in grains grown at elevated temperatures than in grains grown at 18°C.