Rate of photosynthetic induction in fluctuating light varies widely among genotypes of wheat.

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 (Vcmax) 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 (t95) 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 Vcmax 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

Rust resistance in faba bean (Vicia faba L.) : status and strategies for improvement

Faba bean (Vicia faba L.) is an important grain legume used as food and feed. Its production is threatened by abiotic stresses and diseases, of which rust (Uromyces viciae-fabae) is one of the major diseases in East and North Africa, China and the northern grain growing region of Australia. Understanding the genetic and physiological mechanisms of rust resistance in faba bean is in an early phase. The presence of seedling and adult plant resistance genes has been observed. The resistance most frequently utilised in applied plant breeding is race-specific, where the interaction between resistance genes in the host and avirulence genes in the pathogen confers resistance. The main drawback of using race-specific resistance is lack of durability, when deployed singly. Slow rusting or partial resistance, controlled by multiple genes of small effect, is generally non-race specific, so it can be more durable. We present the current knowledge of host resistance and pathogen diversity and propose rational breeding approaches aided with molecular markers to breed durable rust resistance in faba bean.Peer reviewe

Wheat photosystem II heat tolerance: evidence for genotype‐by‐environment interactions

High temperature stress inhibits photosynthesis and threatens wheat production. One measure of photosynthetic heat tolerance is Tcrit – the critical temperature at which incipient damage to photosystem II (PSII) occurs. This trait could be improved in wheat by exploiting genetic variation and genotype-by-environment interactions (GEI). Flag leaf Tcrit of 54 wheat genotypes was evaluated in 12 thermal environments over 3 years in Australia, and analysed using linear mixed models to assess GEI effects. Nine of the 12 environments had significant genetic effects and highly variable broad-sense heritability (H2 ranged from 0.15 to 0.75). Tcrit GEI was variable, with 55.6% of the genetic variance across environments accounted for by the factor analytic model. Mean daily growth temperature in the month preceding anthesis was the most influential environmental driver of Tcrit GEI, suggesting biochemical, physiological and structural adjustments to temperature requiring different durations to manifest. These changes help protect or repair PSII upon exposure to heat stress, and may improve carbon assimilation under high temperature. To support breeding efforts to improve wheat performance under high temperature, we identified genotypes superior to commercial cultivars commonly grown by farmers, and demonstrated potential for developing genotypes with greater photosynthetic heat tolerance

Crop Updates 2000 - Cereals part 1

This session covers eleven papers from different authors: PLENARY PAPERS 1. New Wheat for a Secure, Sustainable Future, Timothy G. Reeves, Sanjaya Rajaram, Maarten van Ginkel, Richard Trethowan, Hans-Joachim Braun, and Kelly Cassaday, International Maize and Wheat Improvement Centre (CIMMYT) 2. Managing Cereal Rusts - a National Perspective, R.A. McIntosh, University of Sydney Plant Breeding Institute, New South Wales 3. Managing Cereal Rusts in 2000 - a regional imperative, R. Loughman, Agriculture Western Australia 4. Is nutrition the answer to wheat after canola problems?Ross Brennan1, Bill Bowden1, Mike Bolland1, Zed Rengel2 and David Isbister2 1 Agriculture Western Australia 2University of Western Australia 5. Improved Sandplain Cropping Systems by Controlled Traffic, Dr Paul Blackwell, Agriculture Western Australia 6. Raised bed farming for improved cropping of waterlogged soils, Derk Bakker, Greg Hamilton, David Houlbrooke, Cliff Spann and Doug Rowe, Agriculture Western Australia 7. Banded Urea increased wheat yields, Patrick Gethin, Stephen Loss, Frank Boetel, and Tim O’Dea, CSBP futurefarm 8. Flexi N is as effective as Urea on wheat and canola, Frank Boetel, Stephen Loss, Patrick Gethin, and Tim O’Dea CSBP futurefarm 9. Why potassium may reduce cereal leaf disease, Noeleen Edwards, Agriculture Western Australia 10, Trace elements, Wayne Pluske CSBP futurefarm, and Ross BrennanAgriculture Western Australia 11. Historical Nutrient Balance at Paddock and Whole Farm scales for typical wheatbelt farms in the Dowerin - Wongan Hills area, M.T.F. Wong, K. Wittwer and H. Zhang Precision Agriculture Research Group, CSIRO Land and Wate

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

Relationship between root morphology and grain yield of wheat in north-western NSW, Australia

Abstract Roots are crucial for water up take and nutrient supply both under water limiting and non-limiting conditions, thus influencing crop water-use-efficiency (WUE) and grain yield. The field experiments were conducted in relatively dry conditions in 2009 to assess the impact of genotypic variation for root traits on WUE and yield. Fifteen wheat genotypes were planted in alpha-lattice designs with three replications and tested under high and low moisture regimes. Genetic variability in root length, root diameter and root length density was determined and the impact of these root traits on above ground traits, water use, water use efficiency and productivity assessed. Significant variation in all root traits was observed among wheat genotypes in both high and low moisture environments. A significant reduction in the overall expression of these root traits was observed in response to water stress. Maximum root trait values were observed near the surface (0-15 cm depth) and these decreased with depth with the exception of root diameter in non-water limiting conditions. Mean root length density in both environments was greater than 0.5 cm 3 cm -3 which was considered sufficient to extract all the moisture from the soil. All root traits were highly heritable and the synthetic derived genotypes were generally superior for all root traits and produced higher grain yield and superior WUE. Stronger relationships between root and above ground traits were observed when water was not limiting. Root traits collectively contributed between 31 and 45% of total variance in improved WUE and grain yield, respectively under water stress and genotypes were identified that extracted water more efficiently under drought resulting in improved WUE and grain yield. It is concluded that under water stress, crop water extraction and adaptation depends on root distribution. The genotypes with superior root characteristics can be combined in crosses with sources of resistance to root diseases, such as crown rot, to improve the adaptation of wheat in north-western NSW. Key words: water deficit, drought, genetic variation, root traits, water use efficiency, wheat. Abbreviations: TRL_total root length (cm) in 0-60 cm soil depth; TRD_total root diameter (mm) in 0-60 cm soil depth; RLD_root length density (cm cm -3 ) in 0-60 cm soil depth; WU a _crop water use at anthesis; WU m _crop water use at maturity; WUE DM _Maturity_water use efficiency for dry matter production at maturity; WUE Grain _water use efficiency for grain yield

Rate of photosynthetic induction in fluctuating light varies widely among genotypes of wheat.

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 (Vcmax) 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 (t95) 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 Vcmax 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

Wide variation in the suboptimal distribution of photosynthetic capacity in relation to light across genotypes of wheat

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

Variation in mesophyll conductance among Australian wheat genotypes

CO2 diffusion from substomatal intercellular cavities to sites of carboxylation in chloroplasts (mesophyll conductance; gm) limits photosynthetic rate and influences leaf intrinsic water-use efficiency (A/gsw). We investigated genotypic variability of g