LEAF POSTURE, GRAIN-YIELD, GROWTH, LEAF STRUCTURE, AND CARBON-ISOTOPE DISCRIMINATION IN WHEAT

The purpose of this study was to examine how differences in leaf angle may affect grain yield of wheat by changes in the relative contribution of yield components or changes in the pattern of crop growth. Leaf structural changes and their influence on plant water status and carbon isotope discrimination were also studied. A collection of pairs of bread wheat (Triticum aestivum L.) lines (PL) differing in leaf angle were grown under irrigation during two consecutive years at Sonora, Mexico. Erect leaf lines did not have higher yields than droopy leaf lines, but erect lines did have 5 to 16% greater number of kernels per unit of ground area. Droopy lines had a lower number of spikes per unit ground area, a greater number of kernels per spike, and a greater weigh of mature kernels than droopy lines. Therefore, the lack of differences in yield apparently was associated with yield component compensation. Differences between PL in discrimination against C-13 (Delta) in mature kernels, relative water content of flag leaves, canopy temperature, leaf area, and degree of leaf tip burning suggested higher transpiration rates (and thus lower water use efficiency) in the erect lines. For example, Delta in kernels was consistently higher in the erect lines than in the droopy lines. In addition there was a significant (r = - 0.85, P < 0.05) negative correlation between canopy temperature during grain filling and Delta. Grain yield was positively correlated (r = 0.50, P < 0.05) with h of kernels. Although wheat genotypes with erect leaves did not show conclusive superiority, nevertheless selection for a more erect growth habit may result in increased yield. However, the possible existence of allometric relationships among leaf erectness and smaller leaves, spikes, and stems make progress in increasing yield a complex task.