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Ultra-early wheat growing systems based on soil temperature triggers for planting instead of arbitrary calendar dates can increase grain yield and overall growing system stability of spring wheat (Triticum aestivum L.) on the northern Great Plains. We conducted field trials at three sites in western Canada from 2017 to 2019 to evaluate the suitability of Canadian spring hexaploid wheat cultivars and market classes for use within ultra-early spring wheat growing systems. All cultivars and classes exhibited improved grain yield stability (lower adjusted coefficient of variation values) and optimal grain yield when planted ultra-early at 2 °C soil temperature rather than delaying planting to 8 °C.

AAC Oravena is a white-hulled spring oat (Avena sativa L.) cultivar selected and developed under organic management. AAC Oravena yields well under organic and conventional production systems, compared with check cultivars. AAC Oravena has good milling quality. AAC Oravena was registered (Reg. No. 7561) by the Variety Registration Office, Canada Food Inspection Agency, on 3 July 2014.

Stripe rust, caused by Puccinia striiformis Westend. f.sp. tritici Erikss. (Pst), is one of the most devastating diseases of wheat (Triticum aestivum L.) globally. Exploring and utilizing new sourc...

Using phenotypic data of four biparental spring wheat populations evaluated at multiple environments under two management systems, we discovered 152 QTL and 22 QTL hotspots, of which two QTL accounted for up to 37% and 58% of the phenotypic variance, consistently detected in all environments, and fell within genomic regions harboring known genes. Identification of the physical positions of quantitative trait loci (QTL) would be highly useful for developing functional markers and comparing QTL results across multiple independent studies. The objectives of the present study were to map and characterize QTL associated with nine agronomic and end-use quality traits (tillering ability, plant height, lodging, grain yield, grain protein content, thousand kernel weight, test weight, sedimentation volume, and falling number) in hard red spring wheat recombinant inbred lines (RILs) using the International Wheat Genome Sequencing Consortium (IWGSC) RefSeq v2.0 physical map. We evaluated a total of 698 RILs from four populations derived from crosses involving seven parents at 3–8 conventionally (high N) and organically (low N) managed field environments. Using the phenotypic data combined across all environments per management, and the physical map between 1058 and 6526 markers per population, we identified 152 QTL associated with the nine traits, of which 29 had moderate and 2 with major effects. Forty-nine of the 152 QTL mapped across 22 QTL hotspot regions with each region coincident to 2–6 traits. Some of the QTL hotspots were physically located close to known genes. QSv.dms-1A and QPht.dms-4B.1 individually explained up to 37% and 58% of the variation in sedimentation volume and plant height, respectively, and had very large LOD scores that varied from 19.0 to 35.7 and from 16.7 to 55.9, respectively. We consistently detected both QTL in the combined and all individual environments, laying solid ground for further characterization and possibly for cloning.

QTL analyses of two bi-parental mapping populations with AC Barrie as a parent revealed numerous FHB-resistance QTL unique to each population and uncovered novel variation near Fhb1. Fusarium head blight (FHB) is a destructive disease of wheat worldwide, leading to severe yield and quality losses. The genetic basis of native FHB resistance was examined in two populations: a recombinant inbred line population from the cross Cutler/AC Barrie and a doubled haploid (DH) population from the cross AC Barrie/Reeder. Numerous QTL were detected among the two mapping populations with many being cross-specific. Photoperiod insensitivity at Ppd-D1 and dwarfing at Rht-B1 and Rht-D1 was associated with increased FHB susceptibility. Anthesis date QTL at or near the Vrn-A1 and Vrn-B1 loci co-located with major FHB-resistance QTL in the AC Barrie/Reeder population. The loci were epistatic for both traits, such that DH lines with both late alleles were considerably later to anthesis and had reduced FHB symptoms (i.e., responsible for the epistatic interaction). Interestingly, AC Barrie contributed FHB resistance near the Fhb1 locus in the Cutler population and susceptibility in the Reeder population. Analyses of the Fhb1 candidate genes PFT and TaHRC confirmed that AC Barrie, Cutler, and Reeder do not carry the Sumai-3 Fhb1 gene. Resistance QTL were also detected at the expected locations of Fhb2 and Fhb5. The native FHB-resistance QTL detected near Fhb1, Fhb2, and Fhb5 do not appear to be as effective as Fhb1, Fhb2, and Fhb5 from Sumai-3. The presence of awns segregated at the B1 awn inhibitor locus in both populations, but was only associated with FHB resistance in the Cutler/AC Barrie population suggesting linkage caused the association rather than pleiotropy.

In previous studies, we reported quantitative trait loci (QTL) associated with the heading, flowering, and maturity time in four hard red spring wheat recombinant inbred line (RIL) populations but the results are scattered in population-specific genetic maps, which is challenging to exploit efficiently in breeding. Here, we mapped and characterized QTL associated with these three earliness traits using the International Wheat Genome Sequencing Consortium (IWGSC) RefSeq v2.0 physical map. Our data consisted of (i) 6526 single nucleotide polymorphisms (SNPs) and two traits evaluated at five conventionally managed environments in the ‘Cutler’ × ‘AC Barrie’ population, (ii) 3158 SNPs and two traits evaluated across three organic and seven conventional managements in the ‘Attila’ × ‘CDC Go’ population, (iii) 5731 SilicoDArT and SNP markers and the three traits evaluated at four conventional and organic management systems in the ‘Peace’ × ‘Carberry’ population, and (iv) 1058 SNPs and two traits evaluated across two conventionally and organically managed environments in the ‘Peace’ × ‘CDC Stanley’ population. Using composite interval mapping, the phenotypic data across all environments, and the IWGSC RefSeq v2.0 physical maps, we identified a total of 44 QTL associated with days to heading (11), flowering (10), and maturity (23). Fifteen of the 44 QTL were common to both conventional and organic management systems, and the remaining QTL were specific to either the conventional (21) or organic (8) management systems. Some QTL harbor known genes, including the Vrn-A1, Vrn-B1, Rht-A1, and Rht-B1 that regulate photoperiodism, flowering time, and plant height in wheat, which lays a solid basis for cloning and further characterization.

Zealand hard red spring wheat (Triticum aestivum L.) was developed using a modified bulk breeding method at the University of Alberta in Edmonton, AB. Zealand is an apically awn-letted, hollow-stemmed cultivar with a combination of high yield potential, tall plant type, large leaves, and early maturity. In three years of testing in the Western Bread Wheat Cooperative Registration Test during 2013–2015, Zealand exhibited grain yield similar to Glenn and Carberry and 5%–6% lower than Unity and AAC Viewfield, though this difference was not significant (p > 0.05). Zealand yielded 37% greater than the highest-yielding Canada Western Red Spring (CWRS) check, CDC Osler, in A-level testing at a certified organic farm. Zealand matured 1–4 d earlier and was taller than all the check cultivars, but exhibited lodging resistance better than Unity and similar to the other checks. The test weight of Zealand (79.1 kg hL−1) was lower than Glenn and similar to the other checks, while its seed mass was in the range of the check cultivars. Overall, Zealand was rated as resistant (R) to the prevalent races of leaf rust, moderately resistant (MR) to stripe rust and loose smut, intermediate (I) to stem rust and leaf spot, and moderately susceptible (MS) to common bunt and Fusarium head blight. Three years of end-use quality evaluation indicated that Zealand is acceptable for the CWRS class, with relatively few weaknesses. The tall plant type, large leaves, and early maturity render Zealand suitable for organic/high weed environments.

Visual diagnosis of plant disease following a visually evident epidemic results in untimely and excessive application of pesticide. Conventional nondestructive testing methods are difficult for early recognition before the onset of symptoms. In this study, tomato mosaic disease and wheat leaf rust were taken as examples. Infrared thermal imaging technology was used to continuously detect the temperature information of the two crops during the incubation period following the introduction of inoculum. Diseases of tomato and wheat were induced by rubbing inoculation and spray inoculation, respectively. Maximum temperature difference (MTD) was calculated to characterize the continuous temperature change during the incubation period. The results showed that the MTD of tomato mosaic disease ranged from 0.2°C ~ 1.7°C, and that of wheat leaf rust 0.4°C ~ 2°C. As the disease progresses, the MTD of both plants showed an increasing trend while the average temperature decreased. The time to observe the symptoms earlier than the naked eye for tomato mosaic and wheat leaf rust is 5d and 7d respectively. Studies showed that it is feasible to realize the early determination of disease through the combination of infrared thermal imaging and MTD calculation. It provides the theoretical basis and method basis for the early and accurate application of spraying.

Pyrenophora tritici-repentis (Ptr), the cause of tan spot of wheat, is a foliar pathogen of economic importance worldwide. Tan spot development is associated with the production of necrotrophic effectors (Ptr ToxA, Ptr ToxB and Ptr ToxC) that serve as fungal pathogenicity and/or virulence factors. The objective of this study was to investigate the sensitivity to each of these effectors in a collection of 100 Canadian wheat cultivars representing all wheat classes and developed over a century by various Canadian breeding programmes. Heterologously expressed, His-tagged Ptr ToxA and Ptr ToxB, and spore germination fluids possessing putative Ptr ToxC activity, were produced and used to screen the cultivars for sensitivity. Of the 100 wheat cultivars tested, 92 were sensitive to at least one effector, 68 were sensitive to Ptr ToxA, 63 were sensitive to Ptr ToxC and 24 were sensitive to Ptr ToxB. Only eight cultivars were insensitive to all three effectors. These results reflect the widespread sensitiv...

Growing resistant wheat (Triticum aestivum L) varieties is an important strategy for the control of leaf rust, caused by Puccinia triticina Eriks. This study sought to identify the chromosomal location and effects of leaf rust resistance loci in five Canadian spring wheat cultivars. The parents and doubled haploid lines of crosses Carberry/AC Cadillac, Carberry/Vesper, Vesper/Lillian, Vesper/Stettler and Stettler/Red Fife were assessed for leaf rust severity and infection response in field nurseries in Canada near Swift Current, SK from 2013 to 2015, Morden, MB from 2015 to 2017 and Brandon, MB in 2016, and in New Zealand near Lincoln in 2014. The populations were genotyped with the 90K Infinium iSelect assay and quantitative trait loci (QTL) analysis was performed. A high density consensus map generated based on 14 doubled haploid populations and integrating SNP and SSR markers was used to compare QTL identified in different populations. AC Cadillac contributed QTL on chromosomes 2A, 3B and 7B (2 loci), Carberry on 1A, 2B (2 loci), 2D, 4B (2 loci), 5A, 6A, 7A and 7D, Lillian on 4A and 7D, Stettler on 2D and 6B, Vesper on 1B, 1D, 2A, 6B and 7B (2 loci), and Red Fife on 7A and 7B. Lillian contributed to a novel locus QLr.spa-4A, and similarly Carberry at QLr.spa-5A. The discovery of novel leaf rust resistance QTL QLr.spa-4A and QLr.spa-5A, and several others in contemporary Canada Western Red Spring wheat varieties is a tremendous addition to our present knowledge of resistance gene deployment in breeding. Carberry demonstrated substantial stacking of genes which could be supplemented with the genes identified in other cultivars with the expectation of increasing efficacy of resistance to leaf rust and longevity with little risk of linkage drag.

Parata is a hard red spring wheat developed at the University of Alberta. In three years of testing in the Parkland Cooperative Registration Test, Parata was higher yielding (P −1, while seed mass was within the range of the check cultivars. Parata was rated resistant to the prevalent races of stem and stripe rust in three years of testing. It was rated R/MR in two years and MS in one year for leaf rust; and was I in two years and S in one year for common bunt. The FHB disease indices for Parata ranged from MS (1 rating) to MR in six station years. Three years of end-use quality evaluation has indicated that Parata is acceptable for the CWRS class, with improvements especially in flour yield and flour ash.

Genetic variation is prerequisite for wheat improvement. High grain yield and protein content and early maturity are some of the major objectives in global as well as Canadian wheat breeding programs. We investigated genetic diversity for earliness related and plant height reducing (Rht) genes in 82 spring wheat cultivars, registered in western Canada, through eight diagnostic DNA markers. Allelic variation was observed at the Vrn-A1, Vrn-B1, Vrn-D1 and Ppd-D1 loci but not at Ppd-A1 and Ppd-B1 loci in the 82 cultivars. Spring type allele of Vrn-A1 was present in 94 % cultivars, whereas only two cultivars carried spring allele of Vrn-D1. Among the four earliness related genes, the most frequent combination was Vrn-A1a, Vrn-B1, vrn-D1 and Ppd-D1b, which was found in 32 cultivars. As for the Rht genes, eight cultivars had Rht-B1b and 13 cultivars had Rht-D1b. All cultivars carrying dominant allele of Vrn-B1, photoperiod-insensitive allele of Ppd-D1 and height reducing allele of Rht-1 had shorter plants and higher grain yield but lower grain protein content. Days to heading and maturity showed positive genetic (rg = 0.65) and phenotypic (rp = 0.44) correlation, and were also positively correlated with grain yield and kernel weight but negatively correlated with test weight and protein content. Plant height was positively correlated with grain protein content (rg = 0.53; rp = 0.42), but negatively correlated with grain yield (rg = −0.47; rp = −0.14). Grain yield and protein content showed negative genetic correlation (rg = −0.57). Among the sixty cultivars from Canada Western Red Spring Class released over 100 years, the newest cultivar yielded 23 % more grain and had 15 % higher grain protein than the oldest cultivar ‘Red Fife’. Breeders in western Canada have incorporated vernalization and photoperiod insensitive and Rht genes in modern cultivars to promote early maturity, to make use of off-season nurseries abroad, and to improve lodging tolerance.

Kubota, H., Quideau, S. A., Hucl, P. J. and Spaner, D. M. 2015. The effect of weeds on soil arbuscular mycorrhizal fungi and agronomic traits in spring wheat (Triticum aestivum L.) under organic management in Canada. Can. J. Plant Sci. 95: 615–627. Understanding the influence of weeds in agroecosystems may aid in developing efficient and sustainable organic wheat production systems. We examined the effect of weeds on soil microbial communities and the performance of spring wheat (Triticum aestivum L.) under organic management in Edmonton, AB, Canada. We grew 13 Canadian spring wheat cultivars in organically managed hand-weeded less-weedy and weedy treatments in 2010 and 2011. The less-weedy treatment exhibited greater grain yield and tillers per square meter, while kernel weight, test weight, days to maturity, plant height, grain P and protein content were not altered by weed treatment. Canada Western Red Spring (CWRS) wheat cultivars CDC Go and CDC Kernen were the most yield-stable because they minimized fertile tiller reduction in response to weed pressure (10 and 13% reduction, respectively, compared with the average reduction of 20%). Other cultivars exhibited yield stability through increased kernel weight. The contribution of arbuscular mycorrhizal fungi (AMF) to the total phospholipid fatty acid increased in both treatments; however, the rate of this increase was greater in the weedy treatment than the less-weedy treatment (from 2.9 to 3.9%, from 2.8 to 3.1%, respectively). Weed dry biomass was positively correlated with AMF% in the less-weedy treatment only. Organic systems tend to be weedier than conventional systems. We found that weeds are important determinants of AMF proliferation in soil. In addition, choosing wheat cultivars that maintain important yield components under severe weed stress is one strategy to maximize yields in organic systems.

A randomly derived recombinant inbred line (RIL) population (n = 163) from a cross between CIMMYT spring wheat ‘Attila’ and the Canadian ‘CDC Go’ was used to map quantitative trait loci (QTL) affecting various agronomic and quality traits. The experiment was also designed to investigate the feasibility of organic wheat breeding by determining selection differentials and the effect of Rht-B1 in paired organic and conventional management systems. Heritability estimates differed between systems for five of nine traits measured; including grain yield, number of tillers, plant height, kernel weight, and grain protein content. Direct selection in each management system resulted in 50% or fewer selected individuals in common between the two systems, for eight of the nine (except for flowering time) studied traits. Most QTL were specific to either the organic or the conventional management system. However, consistent QTL for grain yield, grain volume weight, kernel weight, and days to flowering were mapped in both systems on chromosomes 6A, 1B, 3A, and 5B, respectively. The effect of Rht-B1 was more pronounced in organic systems, where RILs carrying the wild-type allele were taller, produced more grain yield with higher grain protein content, and suppressed weed biomass to a greater extent than those carrying dwarfing alleles. Results of the present study suggest that differences exist between the two management systems for QTL effects. Indirect selection of superior genotypes from one system to another will not result in the advancement of the best possible genotypes. Therefore, selection of spring wheat cultivars for organic systems should be conducted on organically managed lands.

Spring wheat (Triticum aestivum L.) breeding goals in western Canada include good agronomic characteristics and good end-use quality, and also moderate to elevated resistance to diseases of economic importance. In this study, we aimed to identify quantitative trait loci (QTL) associated with resistance to common bunt (Tilletia tritici and Tilletia laevis), tan spot (Pyrenophora tritici-repentis), leaf rust (Puccinia triticina), and stripe rust (Puccinia striiformis f. sp. tritici). A total of 167 recombinant inbred lines (RILs) derived from a cross between two spring wheat cultivars, ‘Attila’ and ‘CDC Go’, were evaluated for reactions to the four diseases in nurseries from three to eight environments, and genotyped with the Wheat 90K SNP array and three gene-specific markers (Ppd-D1, Vrn-A1, and Rht-B1). The RILs exhibited transgressive segregation for all four diseases, and we observed several lines either superior or inferior to the parents. Broad-sense heritability varied from 0.25 for leaf rust to 0.48 for common bunt. Using a subset of 1203 informative markers (1200 SNPs and 3 gene-specific markers) and average disease scores across all environments, we identified two QTLs (QCbt.dms-1B.2 and QCbt.dms-3A) for common bunt, and three QTLs each for tan spot (QTs.dms-2B, QTs.dms-2D, and QTs.dms-6B), leaf rust (QLr.dms-2D.1, QLr.dms-2D.2, and QLr.dms-3A), and stripe rust (QYr.dms-3A, QYr.dms-4A, and QYr.dms-5B). Each QTL individually explained between 5.9 and 18.7% of the phenotypic variation, and altogether explained from 21.5 to 26.5% of phenotypic and from 52.2 to 86.0% of the genetic variation. The resistance alleles for all QTLs except one for stripe rust (QYr.dms-5B) were from CDC Go. Some of the QTLs are novel, while others mapped close to QTLs and/or genes reported in other studies.

We recently reported genomic regions associated with resistance to four wheat diseases and insensitivity to three Pyrenophora tritici-repentis toxins in an association mapping panel consisting of 81 diverse Canadian western spring wheat (Triticum aestivum L.) cultivars. Here, we report genomic regions and SNPs associated with days to heading, plant maturity, plant height, test weight (grain volume weight), grain yield, and grain protein content in the same population using genome-wide association studies (GWAS). The 81 spring wheat cultivars were evaluated for the above six traits across six environments and genotyped with 19,919 polymorphic SNPs and 14 gene-specific markers. Using mixed liner model and a threshold of p ≤ 3.1 × 10−4, we identified a total of 139 significant marker-trait associations that were mapped at 19 genomic regions on 11 chromosomes for heading (3 regions), maturity (2), plant height (3), test weight (3), grain yield (6), and grain protein (2). Each region consisted of clusters of markers ranging from 2 to 33 and individually explained from 4.5 to 26.1% of the phenotypic variation averaged over six environments. Some the genomic regions identified in the present study are novel, while others, such as the regions for grain protein on 1B, days to heading on 5A, plant height on 4B, and test weight on 7A, were located close to either known genes or QTLs reported in previous studies, but direct comparisons in some cases were challenging due to lack of common set of markers and reliable physical positions among the different studies. Results from this study provide additional information to wheat researchers developing improved spring wheat cultivars.

Recently, we mapped genomic regions associated with resistance to wheat diseases and insensitivity to Pyrenophora tritici-repentis (Ptr) toxins using 81 historical and modern Canadian western spring wheat cultivars genotyped with genome-wide single nucleotide polymorphic (SNP) markers. Here, we investigate the frequency and effects of allelic variants of 50 markers associated with 16 candidate genes that regulate resistance to leaf rust (Puccinia triticina), yellow or stripe rust (P. striiformis f. sp. tritici), tan spot (P. tritici-repentis), and Ptr ToxA reaction in a subset of 70 of the 81 spring wheat cultivars. We evaluated the 70 cultivars in the field for all diseases except Ptr ToxA, which was evaluated in a greenhouse. Using Spearman rank correlation, stepwise discriminant analysis, and partial least squares regression, we identified between 4 and 11 markers as best predictors of each phenotypic trait. Overall, 23 of the 50 markers were associated with one or more of the phenotypic traits of which analysis of variance showed significant differences between allelic variants of 19 markers. In most analyses, markers for Lr34/Yr18 and Tsn1 loci were identified consistently as the best predictor of disease resistance and Ptr ToxA sensitivity, respectively. The same alleles from two Lr34/Yr18 diagnostic SNP markers (wMAS000003 and wMAS000004) not only decreased stripe rust scores up to 1.6 (on a 1 to 9 scale), but also increased grain yield up to 196 kg ha−1 without affecting maturity. Results from this study could aid spring wheat breeders in selecting the best parental combinations and/or marker-assisted selection to integrate disease resistance with early maturity and short stature.

There is debate regarding direct or indirect selection for organic conditions. Our objective was to evaluate the progress of indirectly selecting organic cultivars in conventional environments. Canadian spring wheat (Triticum aestivum L.) cultivars, developed for conventional environments from 1885 to 1999 and from 1975 to 2009, respectively, were grown in two separate experiments to assess progress of yield and associated agronomic traits due to breeding. The first experiment evaluated 27 cultivars in organic and conventional conditions for 3 yr (2002, 2003, and 2004), on three sites in western Canada. In the second experiment, eight cultivars were evaluated in organic conditions in 2010 and 2011 at the University of Alberta, Canada. The first experiment showed that breeding had improved yield and most associated traits only in conventional systems and a few associated traits in organic conditions. The second experiment showed that breeding had made significant improvements in yield and test weight in organic conditions. This study suggests that with sufficient quality and disease resistance criteria in place for the breeding of wheat in conventional environments, it may be possible to concomitantly improve wheat yield destined for organic growing conditions. However, fewer associated traits showed significant improvement in organic conditions and improvement rates were lower than in conventional conditions. This suggests that optimizing trait performance in organic conditions should include organic conditions during breeding and selection.

For reproductive success, flowering time must synchronize with favourable environmental conditions. Vernalization genes play a major role in accelerating or delaying the time to flowering. We studied how different vernalization (VRN1) gene combinations alter days to flowering and maturity and consequently the effect on grain yield and other agronomic traits. The study focussed on the effect of the VRN1 gene series (Vrn-A1, Vrn-B1 and Vrn-D1) and their combinations. The Vrn gene group Vrn-A1a, Vrn-B1, vrn-D1 was the earliest to flower and mature, while Vrn-A1b, Vrn-B1, vrn-D1 was the latest to flower. Spring wheat lines with vrn-A1, Vrn-B1, Vrn-D1 were the highest yielding and matured at a similar time as those having vernalization genes Vrn-A1a, Vrn-B1 and Vrn-D1. The findings of this study suggest that the presence of Vrn-D1 has a direct or indirect role in producing higher grain yield. We therefore suggest the introduction of Vrn-D1 allele into higher-yielding classes within Canadian spring wheat germplasm.

Wheat is one of the most widely cultivated crops and, being the staple diet of more than 40 countries, it plays an imperative role in food security. Wheat has remarkable genetic potential to synchronize its flowering time with favourable environmental conditions. This ability to time its flowering is a key factor for its global adaptability and enables wheat plant to produce satisfactory grain yield under very diverse temperature and soil moisture conditions. Vernalization (Vrn), photoperiod (Ppd) and earliness per se (Eps) are the three genetic systems controlling flowering time in wheat. The objective of this review is to provide comprehensive information on the physiological, molecular and biological aspects of the three genetic constituents of flowering and maturity time in wheat. Reviews written in the past have covered either one of the aspects; and generally focused on one of the three genetic constituents of the flowering time. The current review provides (a) a detailed overview of all three gene systems (vernalization, photoperiod and earliness per se) controlling flowering time, (b) details of the primer sequences, their annealing temperatures and expected amplicon sizes for all known markers of detecting vernalization and photoperiod alleles, and (c) an up to date list of QTLs affecting flowering and/or maturity time in wheat.

Published in Agron. J. 105:1695–1706 (2013) doi:10.2134/agronj2013.0192 Available freely online through the author-supported open access option. Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. W production in the prairies of Canada has spanned almost 120 yr. The crop has served producers and end users well, as advancements in cultivar development have produced high-performing, well-adapted, premium quality cultivars. The bread wheat class, or Canada western red spring (CWRS), remains an important export commodity, but other classes of wheat such as Canada prairie spring (CPS) have been developed to serve markets with lower or alternative quality specifications. Some milling markets such as cookie and pastry flour specify low protein and higher starch, which resulted in the creation of the Canada western soft white spring (CWSWS) wheat class. The contrasting quality profiles mean that producers must first decide on a market class and then select cultivars within that class for cultivation. The lack of marketing choice, however, can jeopardize net returns if the wheat produced does not meet quality specifications and is downgraded to feed wheat status. The problem is compounded if the demand for a specific class diminishes due to competition or changes to customer dietary preferences. The latter occurred with the CWSWS class in southern Alberta: the market that once supported >200,000 ha has been reduced to 10,000 ha. As the bioeconomy evolves, opportunities for dual grain markets are emerging. One example is the dramatic expansion of ethanol production in western Canada and the rising demand for a feedstock with high grain yield, low grain protein concentration, and high starch. There are currently seven ethanol plants operating in western Canada with a collective annual output capacity of 509,000,000 L (Collier et al., 2013). Today, a producer of CWSWS and CPS wheat, which are preferred wheat ethanol feedstocks, can now choose to either sell their wheat into a milling market or contract their production to an ethanol plant. This has shifted almost all production of CWSWS away from southern ABSTRACT

Producing higher yields under organic conditions is generally hampered by weeds and lesser nutrient supply. In wheat certain adaptive traits like early season vigour, taller plants, and shorter life cycle have been reported to help plants compete with weeds and produce satisfactory yields. In this experiment we tested the hypothesis ‘that early flowering and maturity conferred by insensitive vernalization alleles Vrn-A1a and/or Vrn-B1 has a yield advantage under organic conditions’ in Canadian spring wheat germplasm. We genotyped 32 cultivars for their vernalization gene composition (Vrn-A1a, Vrn-B1 and Vrn-D1) and studied these cultivars in organic and conventional management systems. We found 88 % of the cultivars possessed vernalization (Vrn) insensitive allele Vrn-A1a either alone or in combination with Vrn-B1. There were no differential affects between the cultivars having insensitive Vrn allele at either single locus (Vrn-A1a) or two (Vrn-A1a, Vrn-B1) under organic and conventional field conditions; except for days to maturity, where cultivars having only Vrn-A1a allele matured earlier. This earlier maturity did not translate to any yield advantage under organic field conditions. Overall, the cultivars grown under organic conditions were earlier flowering, lower yielding with lower test weight compared to the conventional management system. Significant cultivar × environment interactions were found for grain yield, grain protein content and grain fill rate. For grain protein content, cross-over interactions of the cultivars between the management systems were observed. Three cultivars (Marquis, Unity and Minnedosa) exhibited minimal comparative loss in grain yield and grain protein content under organic field conditions, and hence could potentially serve as parents for organic wheat breeding programs.

Isolated microspore culture (IMC) has been used to develop doubled haploid lines and to generate homozygous lines in a single generation for varietal development. Phytosulfokine has been previously used in promoting cell growth and embryo development in various systems. In this study, phytosulfokine alpha (PSK-α) supplemented IMC induction medium was evaluated in triticale and wheat cultivars, and the production of embryo-like structures (ELS), green and albino plants were recorded. In addition, the contribution of ovary co-culture was also evaluated in IMC on a NPB99 + 10F induction medium. Over a range of concentrations up to 10−7M, PSK-α yielded more ELS and green plants in wheat and triticale cultivars at the highest dose, when compared to the control. It also minimized albinism in wheat cultivars, but not in triticale. Interestingly, 10−7M PSK-α also supported the formation of a large number of embryos and a few green plants in the absence of nursing ovaries.

The objective of this study was to determine the effect of induction medium osmolality on embryogenesis and green plant production in wheat and triticale. Isolated microspores of wheat and triticale were subjected to a range of osmolality (300–500 mOsm kg−1) using mannitol. In both species, the maximum number of embryo-like structures (ELS) and green plants were obtained at 350 mOsm kg−1 when the induction medium was supplemented with 9.1 g L−1 of mannitol. A sharp decline in microspore response was observed at higher osmolality. These results demonstrate the effect of osmolality on induction of ELS and production of green plants indicating that the process of microspore embryogenesis can be improved in wheat and triticale by increasing osmolality of the induction medium to 350 mOsm kg−1.

Low frequency of green plant production and albinism limits the use of isolated microspore culture (IMC) in cereal breeding programs. The present study was conducted in triticale and bread wheat IMC to increase the production of green plants and minimize albinism. NPB-99 + 10% Ficoll induction medium was supplemented with mitochondrial or plastid antioxidants, in a completely random design, to evaluate their contribution to successful microspore embryogenesis and green plant production. Each group of antioxidants was tested independently: first in triticale and then validated in various spring wheat genotypes. While the response differed by wheat genotype, induction medium supplemented with proline (10 mM) yielded a greater number of embryos/embryo-like structures and green plants in both triticale and wheat. No differences were found with respect to albinism in triticale or wheat except for the cv. Sadash. Among plastid antioxidants tested, glutathione (2 μM) proved to be the best antioxidant to increase embryo and green plant production. Salicylic acid also helped to reduce the number of albino plants in triticale and the wheat genotype SWS366. Overall, induction medium supplemented with proline or glutathione enhanced microspore embryogenesis in both triticale and wheat and increased the number of green plants in the recalcitrant genotypes.

Recently, we investigated the effect of the wheat 90K single nucleotide polymorphic (SNP) array and three gene-specific (Ppd-D1, Vrn-A1 and Rht-B1) markers on quantitative trait loci (QTL) detection in a recombinant inbred lines (RILs) population derived from a cross between two spring wheat (Triticum aestivum L.) cultivars, 'Attila' and 'CDC Go', and evaluated for eight agronomic traits at three environments under organic management. The objectives of the present study were to investigate the effect of conventional management on QTL detection in the same mapping population using the same set of markers as the organic management and compare the results with organic management. Here, we evaluated 167 RILs for number of tillers (tillering), flowering time, maturity, plant height, test weight (grain volume weight), 1000 kernel weight, grain yield, and grain protein content at seven conventionally managed environments from 2008 to 2014. Using inclusive composite interval mapping (ICIM) on phenotypic data averaged across seven environments and a subset of 1203 informative markers (1200 SNPs and 3 gene specific markers), we identified a total of 14 QTLs associated with flowering time (1), maturity (2), plant height (1), grain yield (1), test weight (2), kernel weight (4), tillering (1) and grain protein content (2). Each QTL individually explained from 6.1 to 18.4% of the phenotypic variance. Overall, the QTLs associated with each trait explained from 9.7 to 35.4% of the phenotypic and from 22.1 to 90.8% of the genetic variance. Three chromosomal regions on chromosomes 2D (61-66 cM), 4B (80-82 cM) and 5A (296-297 cM) harbored clusters of QTLs associated with two to three traits. The coincidental region on chromosome 5A harbored QTL clusters for both flowering and maturity time, and mapped about 2 cM proximal to the Vrn-A1 gene, which was in high linkage disequilibrium (0.70 ≤ r2 ≤ 0.75) with SNP markers that mapped within the QTL confidence interval. Six of the 14 QTLs (one for flowering time and plant height each, and two for maturity and kernel weight each) were common between the conventional and organic management systems, which suggests issues in directly utilizing gene discovery results based on conventional management to make in detail selection (decision) for organic management.

We recently reported three earliness per se quantitative trait loci (QTL) associated with flowering and maturity in a recombinant inbred lines (RILs) population derived from a cross between the spring wheat (Triticum aestivum L.) cultivars ‘Cutler’ and ‘AC Barrie’ using 488 microsatellite and diversity arrays technology (DArT) markers. Here, we present QTLs associated with flowering time, maturity, plant height, and grain yield using high density single nucleotide polymorphic (SNP) markers in the same population. A mapping population of 158 RILs and the two parents were evaluated at five environments for flowering, maturity, plant height and grain yield under field conditions, at two greenhouse environments for flowering, and genotyped with a subset of 1809 SNPs out of the 90K SNP array and 2 functional markers (Ppd-D1 and Rht-D1). Using composite interval mapping on the combined phenotype data across all environments, we identified a total of 19 QTLs associated with flowering time in greenhouse (5), and field (6) conditions, maturity (5), grain yield (2) and plant height (1). We mapped these QTLs on 8 chromosomes and they individually explained between 6.3 and 37.8% of the phenotypic variation. Four of the 19 QTLs were associated with multiple traits, including a QTL on 2D associated with flowering, maturity and grain yield; two QTLs on 4A and 7A associated with flowering and maturity, and another QTL on 4D associated with maturity and plant height. However, only the QTLs on both 2D and 4D had major effects, and they mapped adjacent to well-known photoperiod response Ppd-D1 and height reducing Rht-D1 genes, respectively. The QTL on 2D reduced flowering and maturity time up to 5 days with a yield penalty of 436 kg ha-1, while the QTL on 4D reduced plant height by 13 cm, but increased maturity by 2 days. The high density SNPs allowed us to map eight moderate effect, two major effect, and nine minor effect QTLs that were not identified in our previous study using microsatellite and DArT markers. Results from this study provide additional information to wheat researchers developing early maturing and short stature spring wheat cultivars.

The locus Lr34/Yr18 plays an important role in conferring resistance to a number of fungal diseases and is thus an important component of global wheat breeding efforts. We investigated the differences in disease response and agronomic traits of the ‘CDC Teal’ × ‘CDC Go’ spring wheat population of 187 recombinant inbred lines (RILs) in relation to the presence/absence of the rust resistance gene Lr34/Yr18. Lines carrying the resistant allele of Lr34/Yr18 were taller, matured earlier, and yielded less grain with lower test weights than lines without Lr34/Yr18. Lines with or without the resistant allele of Lr34/Yr18 did not differ for grain protein content, SDS sedimentation volume, and for resistance to leaf spotting and common bunt. Lines with Lr34/Yr18 exhibited lower leaf and stripe rust infection than lines without it. We selected superior lines from the population based on high yield, protein content, SDS sedimentation, and the presence of the resistant allele of Lr34/Yr18 and grew them with continued selection in replicated yield trials over nine site-years. We attempted to combine Lr34/Yr18 with high yield, protein content, and SDS sedimentation suitable for the Canadian western red spring wheat class. Our results suggested that the population size we used was not large enough to obtain recombinants with high yield potential, high grain protein, and acceptable quality attributes. Moreover, selection for Lr34/Yr18 resulted in the elimination of lines with high yield potential. We therefore suggest using a population size of at least 310 to increase the potential of pooling Lr34/Yr18 with high grain yield and desirable agronomic and end-use quality attributes.

Photoperiod response impacts the adaptation of spring wheat (Triticum aestivum L.) to specific areas of the world. Both photoperiod sensitive (PS) and photoperiod insensitive (PI) cultivars are grown successfully in the northern regions of the western United States and the Canadian plains. The goal of the present experiment was to determine the relative performance of PI and PS genotypes as related to planting date and to interpret results in view of climate trends for the region. Three sets of near-isogenic lines that differed for alleles at the Ppd-D1 locus for photoperiod sensitivity were tested at three planting dates in 15 environments in Montana, Washington, Saskatchewan, and Alberta. Results showed that PS lines headed later than PI lines at all planting dates. Grain yield was significantly greater for PS lines at the first two planting dates although no difference between PS and PI lines occurred for the latest planting date. Our results suggest that PS lines are superior to PI lines for this region. This difference is likely to be significant for regional adaptation as planting date becomes earlier due to increasing spring temperatures.

Environmentally smart nitrogen (ESN) is a polymer-coated form of N that provides controlled-release, allowing higher seedplaced safe rates of urea fertilizer. Th e infl uence of coating integrity on the rate of N release in fi eld conditions is unknown. Field studies were conducted from 2008 to 2011 near Lethbridge, AB, Canada, to determine the impact of handling methods on the polymer coating of ESN when seed-placed with canola (Brassica napus L.), wheat (Triticum aestivum L.), or triticale (X Triticosecale Wittmack). Abrasion levels were created through laboratory simulation (0–80% N release aft er 7d in 23°C water, calibrated in increments of 10%; Exp. 1), or from handling by collecting ESN from exit points on nine implements, which was subjected to two methods of loading and unloading at the retail point and farm (9 × 2 × 2 factorial; Exp. 2). Nitrogen release data was related to plant responses in the fi eld by seed placing the ESN at rates of 45 kg N ha –1 with canola and 90 kg N ha –1 for cereals. At the highest N release treatment in Exp. 1, winter cereal and canola stands were reduced by ~30% and spring cereals by 18%. Grain yield was unaff ected in winter wheat but reduced in canola and spring cereals by 20 and 10%, respectively. In Exp. 2, abrasion from transferring ESN in equipment containing scaly deposits or seeders confi gured with header-manifold systems operating at high fan speeds corresponded to higher N release treatments, which reduced winter wheat and canola stands. Crop injury and grain yield, however, was usually mitigated through proper equipment maintenance and settings.

The wheat stem sawfl y (Cephus cinctus Norton (Hymenoptera: Cephidae)) is a serious threat to wheat (Triticum aestivum L.) and other cereal grains in the northern Great Plains. Wheat cultivars with high expression of pith in the culm of the stem (stem solidity) can minimize losses associated with sawfl y infestations and subsequent stem boring of the larva. Based on the widespread area now sown to solid- stemmed wheat, our objective was to develop an integrated nutrient and planting strategy specifi c to solid-stemmed spring wheat using modern farming techniques. Five levels of banded N fertilizer (0, 30, 60, 90, and 120 kg N ha −1 ) were arranged in a factorial combination with three levels of sowing density (100, 300, and 500 seeds m −2 ) and grown at three sites in southern Alberta, Canada, from 2007 to 2009. Increased planting densities optimized yield, but an inverse relationship with pith expression (stem solidness) was observed. Low plant populations (100 seeds m −2 ) were often most effective at maximizing pith expression in solid-stemmed wheat and reducing sawfl y cutting damage. However, this usually required the highest rates of N fertilizer, so a system of low seeding rates and high N may not be economical based on fertilizer input costs and the generally lower grain yield response (−9%). An integrated planting and nutrient strategy for solid-stemmed spring wheat cultivars consists of seeding rates no greater than 300 seeds m −2 and basal N applications in the range of 30 to 60 kg N ha −1 .

Th e wheat stem sawfl y (Cephus cinctus Norton (Hymenoptera: Cephidae)) (WSS) has been a serious pest of wheat (Triticum aesti- vum L.) since the late 19th century. Adoption of solid-stemmed cultivars, which are available only in the spring bread wheat class in Canada, can mitigate damage but the trait that confers resistance tends to be variable. Five other classes of wheat are grown within the geographical range of C. cinctus and are vulnerable to WSS infestation, and the entire production area for durum (T. turgidum L.) in western Canada, Montana, and western North Dakota lies within the geographic range of C. cinctus. Our objective was to test the hypothesis that the response of hollow- and solid-stemmed cultivars to sowing density (150, 250, 350, or 450 seeds m -2 ) would diff er and subsequently aff ect infestation patterns of WSS and an endemic parasitoids. Th e lowest rates of infestation occurred in the hollow-stemmed durum cultivar AC Avonlea and declined with increased sowing density. Wheat pith expression was optimized at the lowest sowing density but the same level produced low and variable grain yield. In the solid- stemmed cultivar Lillian, pith expression was most stable at 250 or 350 seeds m -2 . For all cultivars, grain yield was optimized at the higher seeding rates of 350 and 450 seeds m -2 . Solid-stemmed wheat should be seeded at low to moderate density to maximize resistance to WSS, but hollow-stemmed cultivars should be seeded at higher seeding rates to optimize yield, lower WSS infesta- tion, and to increase overall crop competitiveness.

Most semiarid regions of the northern Great Plains are prone to wheat stem sawfl y (Hymenoptera: Cephidae, Cephus cinctus Norton) attack. As an alternative to the wheat (Triticum aestivum L.)–fallow system, our objective was to determine if continuous cropping infested wheat stubble would inhibit wheat stem sawfl y (WSS) emergence. Adult sawfl y emergence from undisturbed stubble was compared to stubble harrowed with heavy tine or rotary drum harrows before recropping. Adult emergence from a control of “no recropping” was compared to direct seeding infested stubble with (i) air drills confi gured with knife-type openers spaced 23 or 30 cm apart, (ii) an air drill confi gured with high disturbance shovel-type sweep openers, and (iii) a low disturbance air drill equipped with disc openers. Pre-seed heavy tine harrowing reduced adult sawfl y emergence but usually required a high tension setting. No-till planting into infested spring wheat stubble also lowered WSS emergence compared to leaving the fi eld fallow. A system of heavy tine harrows and an air drill equipped with knife openers spaced 30 cm apart reduced WSS adult emergence in spring by 50 to 70%. Grain yield was optimized in spring wheat with air drills equipped with narrow knife openers; in winter wheat optimal yield was obtained with the low disturbance disc drill confi gurations. Our results indicate incremental benefi ts from continuous cropping rather than fallowing fi elds infested with WSS, which is a sustainable alternative to conventional tillage. A systems approach is recommended that integrates these practices with diversifi ed nonhost crop phases and resistant cultivars.

Interest in native species is growing across the tropics as reforestation of degraded lands becomes more widespread. In this study four tree species native to Panama – Cedrela odorata , Pachira quinata , Samanea saman , and Tabebuia rosea – were grown on rural farms at two dry tropical sites in Panama for up to five years. Survivorship and growth data at these “on-farm” trials are compared to data recorded from nearby experimental or “species selection” trial sites and evaluated in terms of soil fertility and management. Participant farmers were also asked about their interest in planting trees in general as well as their interest in 61 species grown in the species selection trial. Although, on-farm survivorship was variable and generally lower than that found on the species selection trial, one species ( S. saman ) experienced high and consistent survivorship. High survivorship combined with growth data from farms at both sites for this species suggests it would be a good candidate for extension projects working with rural farmers. Survivorship of other species appears more sensitive to farmer management and/or local site conditions. Generally lower growth on the Los Santos farms as compared to the species-selection trial is attributed to the lower soil fertility (plant available P) at the on-farm sites compared to the species selection trial. In contrast, only one species – P. quinata – had a growth variable found to be significantly lower between the on-farm and species selection trial sites in Rio Hato. C. odorata , P. quinata T. rosea can all be used in on-farm conditions with consideration to specific site and management conditions. By 2009, approximately 80% of the farmers planting trees still wished to participate in tree planting activities. All of the farmers no longer wishing to continue with the project expressed slow growth rates of trees as a principal reason. All but one of these farmers had growth rates for his/her trees markedly below those of the species selection trial nearby. Some farmers wishing to continue had very high mortality rates (>70% for all species), suggesting non-tangible benefits for participating in project activities. Other species that were not tested on-farm but grew well in the species-selection trials and were of interest to local farmers are discussed. As long as specific site and management conditions are carefully considered, data from species selection trials can be useful in informing tree planting projects with rural farmers; however, care should be taken to manage expectations.

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is historically one of the most important economic insect pests in the northern Great Plains of North America. Within this geographical region, the areas subjected to greatest attack are southern Alberta and Saskatchewan, southwestern Manitoba, eastern and northern Montana, North Dakota, northern South Dakota, and western Minnesota. Cumulative grain-yield losses and annual economic losses associated with this pest can exceed 30% and $350 million, respectively. Solid-stemmed cultivars of common wheat, Triticum aestivum L. (Poaceae), tolerant of infestation, are critical for C. cinctus management, but outbreaks of this pest continue to occur even after six decades of cultivar development. Furthermore, chemical control (a primary control option for other cereal (Poaceae) insect pests) has proven ineffective; this underscores the need to integrate resistant cultivars into a comprehensive integrated pest management program. We provide overviews of wheat stem sawfly biology, recent advances in applied research, the efficacy and integration of cultural and biological management strategies, and future directions for global research activities to manage wheat stem sawfly.

Micronutrient deficiencies in the diet of many people are common and wheat is a staple food crop, providing a carbohydrate and micronutrient source to a large percentage of the world’s population. We conducted a field study to compare five Canadian red spring wheat cultivars (released over the last century) grown under organic and conventional management systems for yield, grain micronutrient concentration, and soil phospholipid fatty acid (PLFA) profile. The organic system had higher grain Zn, Fe, Mg and K levels, but lower Se and Cu levels. There was no trend in the results to suggest that modern western Canadian hard red spring cultivars have lower grain micronutrient content than historical cultivars. Wheat cultivar choice is important for maximizing grain nutrient levels, which was influenced by management system. It is evident that the emphasis on elevated grain quality in the western Canadian hard red spring class has resulted in the retention of micronutrient quality characters. Three fungal PLFAs were indicators for the organic system, and all three of these indicators were positively correlated with grain Cu concentration. In the organic system, percent arbuscular mycorrhizal fungi were negatively correlated with grain Zn and Fe concentrations, and positively correlated with grain Mn, Cu, K concentrations and grain yield. The organic system had higher levels of fungi in the soil, including arbuscular mycorrhizal fungi. Organic management practices appear to result in elevated levels of grain micronutrient concentration. The hard red spring breeding effort in and for the black soil zone of the northern Great Plains also appears to have led to no diminishment of grain micronutrient concentration. It is evident that both the agronomic system and breeding strategies in this region can be exploited for future increases in grain micronutrient concentration.

Breeding spring wheat (Triticum aestivum L.) specifically for organic production has been suggested by producers and researchers alike. To investigate the effects of management systems on selected spring wheat breeding line performance in multi-location tests in the northern Great Plains, we used a randomly derived population of 79 F6-derived recombinant inbred lines (RILs) from a cross between the Canadian hard red spring wheat cultivar AC Barrie and the CIMMYT derived cultivar Attila. The population, including the parents, was grown on conventionally and organically managed land in 12 environments over 3 years. Direct selection in each management system (10% selection intensity based on grain yield) resulted in three lines being retained in each management system, over the multi-location testing. Gains from 10% selection for grain yield in a ‘selection’ year were 3.4 times greater in conventional multi-site yield trials than in organically managed trials. Two lines (BA 05 and BA 36) ranked in the top 10% of both the conventional and organic selection trial of 2005, remained ranked 2nd and 1st, respectively, under conventional management in multi-site yield trials. However, these lines ranked 53rd and 21st, respectively, for grain yield in the multi-site organic yield trials. Selected lines were each yield stable within the management system in which they were selected. Following replicated multi-location yield trials, three lines from the population (BA 02, 29 and 58) ranked within the highest 10% yielding lines in both conventional and organic systems. The results of this study suggest that selection differences occur across multi-location tests, and that selection for grain yield in organic systems should be conducted within organic systems. It is evident, however, that data obtained from conventional yield trials also has some relevance towards breeding for organic environments.

Establishing trees in pastures can have production and conservation benefits, but is complicated by the presence of livestock. The need to protect seedlings from livestock increases tree establishment costs, which in turn, can deter landowners from planting trees. Living fences are a ubiquitous feature of pasture landscapes in the tropics that could help protect newly planted trees by preventing livestock trampling and browsing. This study quantified the effectiveness of a living fence in protecting tree seedlings during the first 2 years after planting. The four native tree species evaluated were: Cedrela odorata L., Pachira quinata (Jacq.) W.S. Alverson, Samanea saman (Jacq.) Merr., and Tabebuia rosea (Bertol.) A. DC. Results show that the living fence provided protection from livestock except in cases where tree species were highly palatable as forage (i.e. P. quinata). Trees planted into the living fence generally had greater survival (62 vs. 28%), relative growth (10.3 times initial height vs. 5.8 times initial height), and final height (191 cm vs. 108 cm) compared to those planted in open pasture after 2 years. However, survival and growth of trees planted into the fence remained lower than that observed at a nearby plantation with no livestock, regular weeding and no living fences. This study indicates that use of living fences as a protective barrier could be an effective low-cost approach for establishing trees in tropical pasture landscapes.

Competition with weeds decreases crop yields globally. Breeding for competitive ability against elevated weed pressure can be difficult because the selection for specific traits which contribute to competitive ability may result in yield losses. The widely studied International Triticeae Mapping Initiative (ITMI) population was used to study the genetics of traits associated with competitive ability in a high latitude (52-53ºN) wheat-growing environment in central Alberta, Canada. Grain yield without weed competition and under experimentally sown cultivated oat competition exhibited similar heritability. Grain yield was positively correlated with early season vigour, and negatively correlated with days to maturity in the competitive treatment only. In this study, similar heritability estimates between competition treatments suggest that selection in a weed free environment can lead to improvements in a weedy environment, but some high-yielding lines under competition would be eliminated during selection.Key words: Wheat, weed competition, competitive ability, International Triticeae Mapping Initiative, genetic correlation

Drought stress is the most important abiotic factor limiting upland rice yields. Identification of quantitative trait loci (QTL) conferring improved drought resistance may facilitate breeding progress. We previously mapped a QTL with a large effect on grain yield under severe drought stress (qtl12.1) in the Vandana/Way Rarem population. In the current paper, we present results from a series of experiments investigating the physiological mechanism(s) by which qtl12.1 affects grain yield under drought conditions. We performed detailed plant water status measurements on a subset of lines having similar crop growth duration but contrasting genotypes at qtl12.1 under field (24 genotypes) and greenhouse (14 genotypes) conditions. The Way Rarem-derived allele of qtl12.1 was confirmed to improve grain yield under drought mainly through a slight improvement (7%) in plant water uptake under water-limited conditions. Such an apparently small increase in water uptake associated with this allele could explain the large effect on yield observed under field conditions. Our results suggest that this improvement of plant water uptake is likely associated with improved root architecture.