Abstract
Since starch is by far the major component of the mature wheat grain, it has been assumed that variation in the capacity for starch synthesis during grain filling can influence final grain weight. We investigated this assumption by studying a total of 54 wheat genotypes including elite varieties and landraces that were grown in two successive years in fields in the east of England. The weight, water content, sugars, starch, and maximum catalytic activities of two enzymes of starch biosynthesis, ADP-glucose pyrophosphorylase and soluble starch synthase, were measured during grain filling. The relationships between these variables and the weights and starch contents of mature grains were analysed. Final grain weight showed few or no significant correlations with enzyme activities, sugar levels, or starch content during grain filling, or with starch content at maturity. We conclude that neither sugar availability nor enzymatic capacity for starch synthesis during grain filling significantly influenced final grain weight in our field conditions. We suggest that final grain weight may be largely determined by developmental processes prior to grain filling. Starch accumulation then fills the grain to a physical limit set by developmental processes. This conclusion is in accord with those from previous studies in which source or sink strength has been artificially manipulated.
Highlights
The aim of this work was to establish whether final grain weight is dependent on the capacity for grain filling in field-grown wheat (Triticum aestivum)
When the whole panel of genotypes was considered together, final grain weights for the genotypes in 2013 were strongly correlated with their final grain weights in 2014.This suggests a relatively small influence of environment on grain weight between these two growing seasons (Fig. 1A; for genotype designations see Supplementary Fig. S1).The starch contents of mature grains varied little with either genotype or year, and there was no significant correlation between starch contents of developing grains in 2013 and 2014 [Fig. 1B; P=0.202 for grains at 20 d after anthesis (DAA), P=0.312 for 30 DAA]
Maximum catalytic activities of ADP-glucose pyrophosphorylase (AGPase) and sucrose content on a fresh-weight basis in developing grains showed little correlation between 2013 and 2014 (Fig. 1C, D). These data suggest that—across the two years of our experiment–final grain weight was under strong genetic control, while starch content, enzyme activity, and sucrose content were more susceptible to environmental modulation
Summary
The aim of this work was to establish whether final grain weight is dependent on the capacity for grain filling (the accumulation of storage products) in field-grown wheat (Triticum aestivum). Numbers of grains per unit land area is a complex, weakly inherited trait, but individual grain weight is more stably inherited (Kuchel et al, 2007; Sadras and Slafer, 2012). There is frequently a trade-off between individual grain weight and grain number, this relationship may not be due to competition (Acreche and Slafer, 2005; Ferrante et al, 2015). It is possible to produce wheat varieties that have both high grain numbers per unit land area and high individual grain weights. Robust quantitative trait loci (QTL) that increase grain weight without reducing grain number have been identified (Simmonds et al, 2014, Griffiths et al, 2015).
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