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Crop photosynthesis and yield are limited by slow photosynthetic induction in sunflecks. We quantified variation in induction kinetics across diverse genotypes of wheat for the first time. Following a preliminary study that hinted at wide variation in induction kinetics across 58 genotypes, we grew 10 genotypes with contrasting responses in a controlled environment and quantified induction kinetics of carboxylation capacity (V cmax) from dynamic A versus ci curves after a shift from low to high light (from 50 μmol m–2 s–1 to 1500 μmol m–2 s–1), in five flag leaves per genotype. Within-genotype median time for 95% induction (t 95) of Vcmax varied 1.8-fold, from 5.2 min to 9.5 min. Our simulations suggest that non-instantaneous induction reduces daily net carbon gain by up to 15%, and that breeding to speed up V cmax induction in the slowest of our 10 genotypes to match that in the fastest genotype could increase daily net carbon gain by up to 3.4%, particularly for leaves in mid-canopy positions (cumulative leaf area index ≤1.5 m² m–2), those that experience predominantly short-duration sunflecks, and those with high photosynthetic capacities.

Abstract Suboptimal distribution of photosynthetic capacity in relation to light among leaves reduces potential whole-canopy photosynthesis. We quantified the degree of suboptimality in 160 genotypes of wheat by directly measuring photosynthetic capacity and daily irradiance in flag and penultimate leaves. Capacity per unit daily irradiance was systematically lower in flag than penultimate leaves in most genotypes, but the ratio (γ) of capacity per unit irradiance between flag and penultimate leaves varied widely across genotypes, from less than 0.5 to over 1.2. Variation in γ was most strongly associated with differences in photosynthetic capacity in penultimate leaves, rather than with flag leaf photosynthesis or canopy light penetration. Preliminary genome-wide association analysis identified nine strong marker-trait associations with this trait, which should be validated in future work in other environments and/or materials. Our modelling suggests canopy photosynthesis could be increased by up to 5 % under sunny conditions by harnessing this variation through selective breeding for increased γ. Plants invest nitrogen in photosynthetic enzymes in leaves. Although the optimal investment should be roughly proportional to how much light each leaf receives, plants tend to underinvest N in upper-canopy (sunlit) leaves. We examined, for the first time, whether this suboptimal pattern differs within species, by measuring light capture and photosynthetic capacity in flag and penultimate leaves across 160 wheat genotypes. We found wide variation in suboptimal N distribution, mostly driven by variation in plants’ ability to move N from penultimate to flag leaves as flag leaves develop. Selecting for less-suboptimal N distribution could increase canopy photosynthesis by several percent.

High temperatures account for major wheat yield losses annually and, as the climate continues to warm, these losses will probably increase. Both photosynthesis and respiration are the main determinants of carbon balance and growth in wheat, and both are sensitive to high temperature. Wheat is able to acclimate photosynthesis and respiration to high temperature, and thus reduce the negative affects on growth. The capacity to adjust these processes to better suit warmer conditions stands as a potential avenue toward reducing heat-induced yield losses in the future. However, much remains to be learnt about such phenomena. Here, we review what is known of high temperature tolerance in wheat, focusing predominantly on the high temperature responses of photosynthesis and respiration. We also identify the many unknowns that surround this area, particularly with respect to the high temperature response of wheat respiration and the consequences of this for growth and yield. It is concluded that further investigation into the response of photosynthesis and respiration to high temperature could present several methods of improving wheat high temperature tolerance. Extending our knowledge in this area could also lead to more immediate benefits, such as the enhancement of current crop models.

Simple and repeatable methods are needed to select for deep roots under field conditions. A large-scale field experiment was conducted to assess the association between canopy temperature (CT) measured by airborne thermography and rooting depth determined by the core-break method. Three wheat populations, C306×Westonia (CW), Hartog×Drysdale (HD), and Sundor×Songlen (SS), were grown on stored soil water in NSW Australia in 2017 (n=196–252). Cool and warm CT extremes (‘tails’) were cored after harvest (13–32% of each population). Rooting depth was significantly correlated with CT at late flowering (r= –0.25, –0.52, and –0.23 for CW, HD, and SS, respectively, P<0.05 hereafter), with normalized difference vegetation index (NDVI) at early grain filling (r=0.30–0.39), and with canopy height (r=0.23–0.48). The cool tails showed significantly deeper roots than the respective warm tails by 8.1 cm and 6.2 cm in CW and HD, and correspondingly, greater yields by an average 19% and 7%, respectively. This study highlighted that CT measured rapidly by airborne thermography or NDVI at early grain filling could be used to guide selection of lines with deeper roots to increase wheat yields. The remote measurement methods in this study were repeatable and high throughput, making them well suited to use in breeding programmes.

Tillering (branching) is a major yield component and, therefore, a target for improving the yield of crops. However, tillering is regulated by complex interactions of endogenous and environmental signals, and the knowledge required to achieve optimal tiller number through genetic and agronomic means is still lacking. Regulatory mechanisms may be revealed through physiological and molecular characterization of naturally occurring and induced tillering mutants in the major crops. Here we characterize a reduced tillering (tin, for tiller inhibition) mutant of wheat (Triticum aestivum). The reduced tillering in tin is due to early cessation of tiller bud outgrowth during the transition of the shoot apex from the vegetative to the reproductive stage. There was no observed difference in the development of the main stem shoot apex between tin and the wild type. However, tin initiated internode development earlier and, unlike the wild type, the basal internodes in tin were solid rather than hollow. We hypothesize that tin represents a novel type of reduced tillering mutant associated with precocious internode elongation that diverts sucrose (Suc) away from developing tillers. Consistent with this hypothesis, we have observed upregulation of a gene induced by Suc starvation, downregulation of a Suc-inducible gene, and a reduced Suc content in dormant tin buds. The increased expression of the wheat Dormancy-associated (DRM1-like) and Teosinte Branched1 (TB1-like) genes and the reduced expression of cell cycle genes also indicate bud dormancy in tin. These results highlight the significance of Suc in shoot branching and the possibility of optimizing tillering by manipulating the timing of internode elongation.

Background and aims Nitrification is the first step in several pathways that lead to losses of nitrogen from agricultural systems. Biological nitrification inhibition (BNI) refers to the ability of some plant species to release chemicals from their roots that inhibit microbial ammonia oxidation thereby decreasing nitrification rates. BNI has been found in the wheat relative Leymus racemosus but not in Triticum aestivum. The aim of this work was to assess a number of landraces of Triticum aestivum for BNI ability. Methods Samples of root exudates and root tissue extracts, collected from hydroponically grown plants, were tested for their impact on nitrification rates when inoculated with pure cultures of two ammonia oxidising bacteria, Nitrosomonas europaea and Nitrosospira multiformis. Pot experiments were then conducted to confirm the results. Results The vast majority of the landraces tested caused some level of inhibition. However, of the 96 wheat landraces tested, 26 produced root exudates which caused a statistically significant reduction in nitrification rates of the two ammonia oxidising bacteria. Root exudates from four of the BNI positive landraces were shown to significantly inhibit nitrification rates in a sandy loam soil. Conclusions This is the first evidence of significant levels of BNI in Triticum aestivum. The discovery of landraces with BNI ability raises the potential for breeding this trait into modern, elite wheat cultivars.

Recent scientific approaches to aesthetics include evolutionary theories about the origin of art behavior, psychological investigations into human aesthetic experience and preferences, and neurophysiological explorations of the mechanisms underlying art experience. Critics of these approaches argue that they are ultimately irrelevant to a philosophical aesthetics because they cannot help us understand the distinctive conceptual basis and normativity of our art experience. This criticism may seem plausible given the piecemeal nature of these scientific approaches, but a more comprehensive naturalistic framework can help us understand the conceptual basis and normativity of art. In particular, the ecology of art, an understanding of how individuals interact within particular environments, can help us understand the engineered art niches in which we create and experience art. Each niche is associated with a particular deme, or set of individuals that interact within that niche, and a set of cognitive, epistemic, and pedagogical technologies that form the conceptual basis of a niche-dependent normativity. This is to be contrasted with the niche-independent normativity revealed by many of the scientific approaches. This framework, and the conflicting streams of normativity it reveals, allows us to better understand conflicts in normativity and the implausibility of unequivocal and universal normative principles.

The duration of pre-anthesis developmental phases is of interest in breeding for improved adaptation and yield potential in temperate cereals. Yet despite numerous studies on the genetic control of anthesis (flowering) time and floral initiation, little is known about the genetic control of other pre-anthesis phases. Furthermore, little is known about the effect that changes in the duration of pre-anthesis phases could have on traits related to leaf appearance and tillering, or dry matter accumulation before terminal spikelet initiation (TS). The genetic control of the leaf and spikelet initiation phase (LS; from sowing to TS), the stem elongation phase (SE; from TS to anthesis), and, within the latter, from TS to flag leaf appearance and from then to anthesis, was studied in two doubled-haploid, mapping bread wheat populations, Cranbrook×Halberd and CD87×Katepwa, in two field experiments (ACT and NSW, Australia). The lengths of phases were estimated from measurements of both TS and the onset of stem elongation. Dry weight per plant before TS, rate of leaf appearance, tillering rate, maximum number of tillers and number of leaves, and dry weight per plant at TS were also estimated in the Cranbrook×Halberd population. More genomic regions were identified for the length of the different pre-anthesis phases than for total time to anthesis. Although overall genetic correlations between LS and SE were significant and positive, independent genetic variability between LS and SE, and several quantitative trait loci (QTLs) with different effects on both phases were found in the two populations. Several of these QTLs (which did not seem to coincide with reported major genes) could be of interest for breeding purposes since they were only significant for either LS or SE. There was no relationship between LS and the rate of leaf appearance. LS was strongly and positively correlated with dry weight at TS but only slightly negatively correlated with early vigour (dry weight before TS). Despite significant genetic correlations between LS and some tillering traits, shortening LS so as to lengthen SE without modifying total time to anthesis would not necessarily reduce tillering capacity, as QTLs for tillering traits did not coincide with those QTLs significant only for LS or SE. Therefore, the study of different pre-anthesis phases is relevant for a better understanding of genetic factors regulating developmental time and may offer new tools for fine-tuning it in breeding for both adaptability and yield potential.