Cereal production systems are increasingly threatened by suboptimal water supply or intermittent drought spells early in the planting season. Seed coated with hydrophilic materials or hydro-absorbers that increase the amount of water available for germination and seedling development is a promising approach to improving stand establishment under changing conditions. Barley, rye and wheat grains with combinations of hydro-absorber, humic acid and Biplantol in different shares of the total seed mass were germinated in plates at 25°C on moist filter paper. Germination rates, resource partitioning and mobilization efficiency were assessed and compared with those of uncoated seeds. Results show a strong influence of coat thickness and composition on the germination rate and the efficiency of mobilization of carbohydrates stored in the endosperm. In general, coating significantly reduced germination rate and total germination as compared to uncoated seeds in all cereals tested. Differences in coating thickness had a distinct effect on germination rate for most combinations of coatings and species. Germination rates increased with increasing coat size. This effect was most pronounced for coatings containing hydro-absorbers and least pronounced for coatings containing humic acid or Biplantol. Coating generally increased the amount of carbohydrates partitioned to the roots, and thick coating increased the efficiency of grain reserve mobilization compared with the uncoated seeds. Differences between species and the implications for coating-related changes in germination metabolism are discussed.
