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Growth and Final Weight of Central and Lateral Barley Grains under Mediterranean Conditions as Influenced by Sink Strength

Area de Conreus Extensius, Centre UdL-IRTA, Rovira Roure 177, Lleida 25198, Spain

J. L. Araus^*

Unitat de Fisiologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Barcelona 08028, Spain

^* Corresponding author (josel{at}porthos.bio.ub.es).

Grain weight largely determines the end-use quality of barley (Hordeum vulgare L.). In six-rowed types, central spikelets commonly bear heavier grains than lateral spikelets. However, the extent to which such differences in weight are influenced by source availability remains unclear. Field experiments were carried out in nine rainfed trials of northeastern Spain and showed large variability in grain weight. Three six-rowed genotypes were used: Barberousse, Orria, and Plaisant. Sink strength 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 filling duration (GFD)] and in final grain weight was evaluated in control and sink-reduced spikes. Central grains outweighed lateral ones in control spikes from 7.3 to 14.8 mg across trials. Absolute differences in weight increased progressively in those trials favoring larger grains, although lateral to central grain weight ratios (L/C) remained fairly constant, with an average value of 0.77. This advantage of central grains was mostly caused by higher GFR values. A 50%-reduced sink increased grain weight of both central and lateral spikelets similarly and did not diminish the absolute differences in weight found in control spikes. This result suggests that central grains have a greater intrinsic potential weight. While grain yield was partially source limited in all environments, lateral grains exhibited on average a major degree of source limitation (24.2%) than central grains (19.1%). Sink reduction increased grain weight of both central and lateral grains by stimulating GFR in all trials, and also by lengthening GFD in poor rainfed environments.

Received for publication February 3, 1997.