Grain size and nitrogen accumulation in sink-reduced barley under Mediterranean conditions

In rainfed Mediterranean environments, grain growth of barley is often hindered by the occurrence of unpredictable terminal stresses such as drought or high temperature. To study the effect of an enhancement in the assimilate availability on final grain size, a 50% sink-reduction was done in the mainstems of three six-row barley cultivars (Hordeum vulgare L.). The study was conducted in 11 field trials during four years in northeast Spain. The average grain size of control spikes varied significantly among trials between 26.4 mg and 49.1 mg. The average increase of grain size in response to a 50% sink-reduction was 20%. These increments were progressively greater in trials with small grains of control spikes, indicating a major degree of source Limitation in low-yielding rainfed environments. Total N content per grain showed a larger average increase (47.6%) in sink-reduced spikes. N accumulated uniformly across trials in response to sink manipulation, indicating that environmental conditions did not limit protein synthesis during gain filling. Dry matter increments in response to sink halving were mainly due to protein accumulation when environmental conditions determined large grains, suggesting that a sink limitation for carbohydrate accumulation may also occur under Mediterranean conditions. (C) Elsevier Science B.V. All rights reserved.