Grain number and grain weight in wheat lines contrasting for stem water soluble carbohydrate concentration

In wheat, the ability to store and remobilise large amounts of stern water soluble carbohydrates (WSC) to grain constitutes a desirable trait to incorporate into germplasm targeted to regions with frequent terminal drought. The main aim of this paper was to examine the relationships between WSC storage, grain number and grain weight across several environments. A small set of recombinant inbred lines (2-4) contrasting in stem WSC were grown in six field trials where water availability, sowing date and/or N level were manipulated, with line yields ranging from 400 to 850 g m(-2) across experiments. Biomass, N and WSC concentration (WSCc, mg g(-1) dry weight) and amount (WSCa, g m(-2)) were monitored. A resource-oriented area-based model [Fischer, R.A., 1984. Growth and yield of wheat. In: Smith, W.H., Bante, S.J. (Eds.), Potential Productivity of Field Crops Under Different Environments. International Rice Research Institute, Los Banos, pp. 129-154] and intrinsic rates of organ growth were used to investigate the consequences on grain number of potential competition between spike and stem around flowering. Early sown irrigated trials allowed consistent genotypic discrimination for WSCc and WSCa. High WSC lines had similar or higher yields compared to low WSC lines. High WSC lines had consistently lower grain number m(-2) linked to a lower number of spikes and sterns m(-2), higher individual grain weight under irrigated or more limited conditions, and individual sterns with less structural biomass. The changes in plant type associated with the high WSC phenotype, mainly fewer steins and a high individual grain weight, may contribute to its moderate yield advantage despite the lower grain number m(-2). A model based on resource capture per unit area around flowering was not sufficient alone to explain the differences between lines in grain number m(-2). We propose that linking a resource-based model with additional understanding of controls of crop morphology would improve the prediction of differences in yield components in related genetic material. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.