GROWTH AND FINAL WEIGHT OF CENTRAL AND LATERAL BARLEY GRAINS UNDER MEDITERRANEAN CONDITIONS AS INFLUENCED BY SINK STRENGTH

Grain weight largely determines the end-use quality of barley (Hordeum vulgare L.),In six-rowed types, central spikelets commonly bear heavi er grains than lateral spikelets. However, the extent to which such di fferences in weight are influenced by source availability remains uncl ear, Field experiments were carried out in nine rainfed trials of nort heastern Spain and showed large variability in grain weight Three six- rowed genotypes were used: Barberousse, Orria, and Plaisant. Sink stre ngth of mainstems was decreased by half at anthesis by sterilizing 50% of fertile central and lateral florets. Variation among spikelets in grain growth parameters [maximum grain filling rate (GFR) and grain fi lling duration (GFD)] and in final grain weight was evaluated in contr ol and sink-reduced spikes. Central gains outweighed lateral ones in c ontrol spikes from 7.3 to 14.8 mg across trials, Absolute differences in weight increased progressively in those trials favoring larger grai ns, although lateral to central grain weight ratios (L/C) remained fai rly constant, with an average value of 0.77. This advantage of central grains was mostly caused by higher GFR values. A 50%-reduced sink inc reased grain weight of both central and lateral spikelets similarly an d did not diminish the absolute differences in weight found in control spikes. This result suggests that central gains have a greater intrin sic potential weight While gain yield was partially source limited in all environments, lateral grains exhibited on average a major degree o f source limitation (24.2%) than central grains (19.1%). Sink reductio n increased gain weight of both central and lateral grains by stimulat ing GFR in all trials, and also by lengthening GFD in poor rainfed env ironments.