Competition from weeds can reduce grain yields in both conventional and organic systems. Plant height, tillering, and elevated photosynthetically active radiation interception are some of the traits thought to help confer competitive ability in cereal grains. Crop cultivars developed before the advent of modern, high‐input agriculture may be better suited to lower soil nutrient levels and elevated weed competition. Twenty‐seven spring bread wheat (Triticum aestivum L.) cultivars, representing 114 yr of Canadian wheat breeding, were grown at conventionally and organically managed sites in north central Alberta over a 3‐yr period. Average conventional yields were 63% greater than organic yields, and average overall weed biomass was significantly greater under organic management. Earlier flowering and maturity were more important for achieving high grain yield in organic fields than in conventional fields. Greater numbers of spikes m−2 were associated with increased grain yield in organic fields but were not in conventional fields. In organic fields, increased plant height and early maturity were associated with reduced weed biomass, while strong early season vigor was related to increased yield, increased spikes m−2, and reduced weed biomass. A competitive crop ideotype for organically grown spring wheat in northern growing regions of the Canadian Prairies should include taller plants, with fast early season growth, early maturity, and elevated fertile tiller number.

In the past, there have been drought events in different parts of the world, which have negatively influenced the productivity and production of various crops including wheat (Triticum aestivum L.), one of the world's three important cereal crops. Breeding new high yielding drought-tolerant wheat varieties is a research priority specifically in regions where climate change is predicted to result in more drought conditions. Commonly in breeding for drought tolerance, grain yield is the basis for selection, but it is a complex, late-stage trait, affected by many factors aside from drought. A strategy that evaluates genotypes for physiological responses to drought at earlier growth stages may be more targeted to drought and time efficient. Such an approach may be enabled by recent advances in high-throughput phenotyping platforms (HTPPs). In addition, the success of new genomic and molecular approaches rely on the quality of phenotypic data which is utilized to dissect the genetics of complex traits such as drought tolerance. Therefore, the first objective of this review is to describe the growth-stage based physio-morphological traits that could be targeted by breeders to develop droughttolerant wheat genotypes. The second objective is to describe recent advances in high throughput phenotyping of drought tolerance related physio-morphological traits primarily under field conditions. We discuss how these strategies can be integrated into a comprehensive breeding program to mitigate the impacts of climate change. The review concludes that there is a need for comprehensive high throughput phenotyping of physio-morphological traits that is growth stage-based to improve the efficiency of breeding drought-tolerant wheat.

BackgroundCommon bacterial blight (CBB), incited by Xanthomonas axonopodis pv. phaseoli (Xap), is a major yield-limiting factor of common bean (Phaseolus vulgaris L.) production around the world. Host resistance is practically the most effective and environmentally-sound approach to control CBB. Unlike conventional QTL discovery strategies, in which bi-parental populations (F2, RIL, or DH) need to be developed, association mapping-based strategies can use plant breeding populations to synchronize QTL discovery and cultivar development.ResultsA population of 469 dry bean lines of different market classes representing plant materials routinely developed in a bean breeding program were used. Of them, 395 lines were evaluated for CBB resistance at 14 and 21 DAI (Days After Inoculation) in the summer of 2009 in an artificially inoculated CBB nursery in south-western Ontario. All lines were genotyped using 132 SNPs (Single Nucleotide Polymorphisms) evenly distributed across the genome. Of the 132 SNPs, 26 SNPs had more than 20% missing data, 12 SNPs were monomorphic, and 17 SNPs had a MAF (Minor Allelic Frequency) of less than 0.20, therefore only 75 SNPs were used for association study, based on one SNP per locus. The best possible population structure was to assign 36% and 64% of the lines into Andean and Mesoamerican subgroups, respectively. Kinship analysis also revealed complex familial relationships among all lines, which corresponds with the known pedigree history. MLM (Mixed Linear Model) analysis, including population structure and kinship, was used to discover marker-trait associations. Eighteen and 22 markers were significantly associated with CBB rating at 14 and 21 DAI, respectively. Fourteen markers were significant for both dates and the markers UBC420, SU91, g321, g471, and g796 were highly significant (p ≤ 0.001). Furthermore, 12 significant SNP markers were co-localized with or close to the CBB-QTLs identified previously in bi-parental QTL mapping studies.ConclusionsThis study demonstrated that association mapping using a reasonable number of markers, distributed across the genome and with application of plant materials that are routinely developed in a plant breeding program can detect significant QTLs for traits of interest.

Organically managed production systems often experience greater weed pressure than their conventional counterparts, potentially causing yield losses and increased weed seed build‐up. The use of competitive crop cultivars and the cultural practice of increasing seeding rates may moderate such production constraints. Field trials were conducted at two organically managed locations in Alberta, Canada for 2 yr to determine the effect of competition with tame oat (Avena sativa L.), cultivar, and crop seeding rate (300 and 600 seeds m−2) on the competitive ability and agronomic performance of Canadian spring wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Cultivars were selected based on their differing heights, tillering capacities, and times to maturity. Simulated weed competition from tame oat reduced grain yield by an average of 27%. Barley cultivars were generally more competitive than wheat cultivars. Height and early maturity were more closely associated with weed suppression and yield maintenance than tillering capacity. The modern semidwarf CDC Go was the highest yielding wheat cultivar, but was a poor weed suppressor. Doubling the seeding rate increased grain yield and weed suppression. This effect was not cultivar specific, which implies that doubling the seeding rate may be a generally effective method of overcoming yield losses and weed seed build‐up associated with increased weed populations under organic production.

1129 RESEARCH M any wheat (Triticum aestivum L.) breeding objectives for organically managed systems (including grain yield, resistance to abiotic and biotic stresses, and baking quality) are similar to conventionally managed systems. It may be, however, necessary to test the expression of these traits under low input, very weedy organic conditions to maximize gain from selection in organic environments. A few traits relevant to high input farming may have negative effects on organic lands. The breeding for semidwarf wheat cultivars as a result of the green revolution has resulted in (i) reduced depth and size of root systems, (ii) increased reliance on N fertilizers to attain satisfactory protein content, (iii) ABSTRACT 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.

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.

Earliness per se regulates flowering time independent of environmental signals and helps to fine tune the time of flowering and maturity. In this study, we aimed to map earliness per se quantitative trait loci (QTLs) affecting days to flowering and maturity in a population developed by crossing two spring wheat cultivars, Cutler and AC Barrie. The population of 177 recombinant inbred lines (RILs) was genotyped for a total of 488 SSR and DArT polymorphic markers on all 21 chromosomes. Three QTLs of earliness per se affecting days to flowering and maturity were mapped on chromosomes 1B (QEps.dms-1B1 and QEps.dms-1B2) and 5B (QEps.dms-5B1), in individual environments and when all the environments were combined. A QTL affecting flowering time (QFlt.dms-4A1) was identified on chromosome 4A. Two grain yield QTLs were mapped on chromosome 5B, while one QTL was mapped on chromosome 1D. The population segregated for the photoperiod insensitive gene, Ppd-D1a, and it induced earlier flowering by 0.69 days and maturity by 1.28 days. The photoperiod insensitive allele Ppd-D1a interacted in an additive fashion with QTLs for flowering and maturity times. The earliness per se QTL QFlt.dms-5B.1 inducing earlier flowering could help to elongate grain filling duration for higher grain yield. Hence, chromosome 5B possesses promising genomic regions that may be introgressed for higher grain yield with earlier maturity through marker-assisted selection in bread wheat.

Vernalization response (Vrn) genes play a major role in determining the flowering/maturity times of spring-sown wheat. We characterized a representative set of 40 western Canadian adapted spring wheat cultivars/lines for 3 Vrn loci. The 40 genotypes were screened, along with 4 genotypes of known Vrn genes, using previously published genome-specific polymerase chain reaction primers designed for detecting the presence or absence of dominant or recessive alleles of the major Vrn loci: Vrn-A1, Vrn-B1, and Vrn-D1. The dominant promoter duplication allele Vrn-A1a was present in 34 of 40 cultivars/lines, whereas the promoter deletion allele Vrn-A1b was present in only 1 of the western Canadian cultivars (Triticum aestivum L. 'Rescue') and 2 of its derivative chromosomal substitution lines. The intron deletion allele Vrn-A1c was not present in any line tested. Only 4 of the western Canadian spring wheat cultivars tested here carry the recessive vrn-A1 allele. The dominant allele of Vrn-B1 was detected in 20 cultivars/lines. Fourteen cultivars/lines had dominant alleles of Vrn-A1a and Vrn-B1 in combination. All cultivars/lines carried the recessive allele for Vrn-D1. The predominance of the dominant allele Vrn-A1a in Canadian spring wheat appears to be due to the allele's vernalization insensitivity, which confers earliness under nonvernalizing growing conditions. Wheat breeders in western Canada have incorporated the Vrn-A1a allele into spring wheats mainly by selecting for early genotypes for a short growing season, thereby avoiding early and late season frosts. For the development of early maturing cultivars with high yield potential, different combinations of Vrn alleles may be incorporated into spring wheat breeding programs in western Canada.