Ear and flag leaf photosynthesis of awned and awnless Triticum species

SUMMARY The net photosynthetic rates of ears and flag leaves of awned and awnless wheats were measured by infra‐red gas analysis in a controlled environment experiment. At 107 W m ‐2 the rates of net photosynthesis of the ears of two awned Triticum aestivum lines were two to three times greater than those of their isogenic awnless counterparts. The net rates of photosynthesis of the flag leaves of all four lines were, however, similar. Net photosynthetic rates of ears of T. durum and T. turgidum , which have much larger awns, were considerably higher than those of T. aestivum. Between 70 and 90% of carbon‐14 assimilated by the flag leaves and by the ears of T. aestivum was translocated to the grains, with no effect of awns in this respect. In a glasshouse experiment with detached shoots the contributions of the component organs to gross photosynthesis were determined by carbon‐14 labelling. Ears of awnless lines of T. aestivum contributed about 10% to the photosynthesis of the organs above the node of the penultimate leaf and awns increased this to about 18%. Fixation by awned ears of T. durum and T. turgidum was 21–29% and of this 78–86% was contributed by the awns. In both experiments the contribution of the flag leaf to shoot photosynthesis was greater in T. aestivum than in the other species.