Awns reduce grain number to increase grain size and harvestable yield in irrigated and rainfed spring wheat.

Genotypic variation in ear morphology is linked to differences in photosynthetic potential to influence grain yield in winter cereals. Awns contribute to photosynthesis, particularly under water-limited conditions when canopy assimilation is restricted. We assessed performance of up to 45 backcross-derived, awned-awnletted NILs representing four diverse genetic backgrounds in 25 irrigated or rainfed, and droughted environments in Australia and Mexico. Mean environment grain yields were wide-ranging (1.38-7.93 t ha(-1)) with vegetative and maturity biomass, plant height, anthesis date, spike number, and harvest index all similar (P >0.05) for awned and awnletted NILs. Overall, grain yields of awned-awnletted sister-NILs were equivalent, irrespective of yield potential and genetic background. Awnletted wheats produced significantly more grains per unit area (+4%) and per spike (+5%) reflecting more fertile spikelets and grains in tertiary florets. Increases in grain number were compensated for by significant reductions in grain size (-5%) and increased frequency (+0.8%) of small, shrivelled grains ('screenings') to reduce seed-lot quality of awnletted NILs. Post-anthesis canopies of awnletted NILs were marginally warmer over all environments (+0.27 °C) but were not different and were sometimes cooler than awned NILs at cooler air temperatures. Awns develop early and represented up to 40% of total spikelet biomass prior to ear emergence. We hypothesize that the allocation of assimilate to large and rapidly developing awns decreases spikelet number and floret fertility to reduce grain number, particularly in distal florets. Individual grain size is increased to reduce screenings and to increase test weight and milling quality, particularly in droughted environments. Despite the average reduction in grain size, awnless lines could be identified that combined higher grain yield with larger grain size, increased grain protein concentration, and reduced screenings.

A paradigm shift towards low-nitrifying production systems: the role of biological nitrification inhibition (BNI).

BACKGROUND: Agriculture is the single largest geo-engineering initiative that humans have initiated on planet Earth, largely through the introduction of unprecedented amounts of reactive nitrogen (N) into ecosystems. A major portion of this reactive N applied as fertilizer leaks into the environment in massive amounts, with cascading negative effects on ecosystem health and function. Natural ecosystems utilize many of the multiple pathways in the N cycle to regulate N flow. In contrast, the massive amounts of N currently applied to agricultural systems cycle primarily through the nitrification pathway, a single inefficient route that channels much of this reactive N into the environment. This is largely due to the rapid nitrifying soil environment of present-day agricultural systems. SCOPE: In this Viewpoint paper, the importance of regulating nitrification as a strategy to minimize N leakage and to improve N-use efficiency (NUE) in agricultural systems is highlighted. The ability to suppress soil nitrification by the release of nitrification inhibitors from plant roots is termed 'biological nitrification inhibition' (BNI), an active plant-mediated natural function that can limit the amount of N cycling via the nitrification pathway. The development of a bioassay using luminescent Nitrosomonas to quantify nitrification inhibitory activity from roots has facilitated the characterization of BNI function. Release of BNIs from roots is a tightly regulated physiological process, with extensive genetic variability found in selected crops and pasture grasses. Here, the current status of understanding of the BNI function is reviewed using Brachiaria forage grasses, wheat and sorghum to illustrate how BNI function can be utilized for achieving low-nitrifying agricultural systems. A fundamental shift towards ammonium (NH4(+))-dominated agricultural systems could be achieved by using crops and pastures with high BNI capacities. When viewed from an agricultural and environmental perspective, the BNI function in plants could potentially have a large influence on biogeochemical cycling and closure of the N loop in crop-livestock systems.

Molecular mapping of genes for Coleoptile growth in bread wheat (Triticum aestivum L.).

Successful plant establishment is critical to the development of high-yielding crops. Short coleoptiles can reduce seedling emergence particularly when seed is sown deep as occurs when moisture necessary for germination is deep in the subsoil. Detailed molecular maps for a range of wheat doubled-haploid populations (Cranbrook/Halberd, Sunco/Tasman, CD87/Katepwa and Kukri/Janz) were used to identify genomic regions affecting coleoptile characteristics length, cross-sectional area and degree of spiralling across contrasting soil temperatures. Genotypic variation was large and distributions of genotype means were approximately normal with evidence for transgressive segregation. Narrow-sense heritabilities were high for coleoptile length and cross-sectional area indicating a strong genetic basis for differences among progeny. In contrast, heritabilities for coleoptile spiralling were small. Molecular marker analyses identified a number of significant quantitative trait loci (QTL) for coleoptile growth. Many of the coleoptile growth QTL mapped directly to the Rht-B1 or Rht-D1 dwarfing gene loci conferring reduced cell size through insensitivity to endogenous gibberellins. Other QTL for coleoptile growth were identified throughout the genome. Epistatic interactions were small or non-existent, and there was little evidence for any QTL x temperature interaction. Gene effects at significant QTL were approximately one-half to one-quarter the size of effects at the Rht-B1 and Rht-D1 regions. However, selection at these QTL could together alter coleoptile length by up to 50 mm. In addition to Rht-B1b and Rht-D1b, genomic regions on chromosomes 2B, 2D, 4A, 5D and 6B were repeatable across two or more populations suggesting their potential value for use in breeding and marker-aided selection for greater coleoptile length and improved establishment.