Genotypic Differences in Photosynthetic Contributions of Plant Parts to Grain Yield in Oats1

The photosynthetic contribution of panicles, leaf sheaths and stems, flag‐leaf blade, and other leaf blades to grain yield was determined for two oat genotypes, 'A‐465' (large‐glumed, moderately dense leaf canopy with "drooping" leaf blades) and 'Goodfield' (small‐glumed, sparse leaf canopy with erect leaf blades). Contribution to yield was assessed by shading or removing the various plant parts and measuring the decrease in grain dry weight caused by the treatments over a 17‐day period. Photosynthesis in the panicle, leaf sheaths and stems, flag‐leaf blade, and other leaf blades accounted for 63, 15, 18, and 4% (ns) of the grain weight in A‐465 and 38, 26, 10 (ns), and 26% in Goodfield. The greater contribution of panicles in A‐465 is believed due to the large glume area of this genotype. The differential contribution of the genotypes from leaf canopy below the flag‐leaf blade (19% in A‐465, 52% in Goodfield) may be associated with either leaf canopy morphology (Goodfield has an erectophile canopy) or the earlier senescence of leaves of A‐465. It is suggested that a high panicle capacity for photosynthesis would be beneficial because (1) panicle tissue may be more efficient, (2) panicle tissue would still photosynthesize under conditions of leaf disease epiphytotic, and (3) panicle tissue may remain physiologically active longer than leaf tissue.