First report of glyphosate-resistant downy brome (Bromus tectorum L.) in Canada.

Glyphosate is the most used herbicide worldwide, and is an important source of economical weed control in glyphosate-resistant crops, and conservation tillage systems, among other uses. Downy brome (Bromus tectorum L.), otherwise known as cheatgrass, is a highly invasive winter-annual grass weed in cropping systems, pastureland, and naturalized or ruderal areas in western North America. In 2021, a downy brome population remained uncontrolled following four applications of glyphosate in a glyphosate-resistant canola (Brassica napus L.) field located in Taber County, Alberta, Canada. All individuals from the subsequent generation of the population survived glyphosate treatment at the typical field rate (900 g ae ha-1). In dose-response bioassays, the putative glyphosate-resistant population exhibited 10.6- to 11.9-fold, 7.7- to 8.7-fold, 7.8- to 8.8-fold, and 8.3- to 9.5-fold resistance to glyphosate based on plant survival, visible control, and biomass fresh weight and dry weight, respectively, compared with two susceptible populations 21 days after treatment. Estimated glyphosate rates for 80% control of this population ranged from 2795 to 4511 g ae ha-1; well above common usage rates. This downy brome population represents the first glyphosate-resistant grass weed confirmed in Canada, and the second weed species exhibiting glyphosate resistance in the Canadian prairie region.

Multi-year and multi-site effects of recurrent glyphosate applications on the wheat rhizosphere microbiome.

Glyphosate (N-(phosphonomethyl)glycine) is broad-spectrum herbicide that is extensively used worldwide, but its effects on the soil microbiome are inconsistent. To provide a sound scientific basis for herbicide re-review and registration decisions, we conducted a four-year (2013-2016) study in which we consecutively applied glyphosate to a wheat (Triticum aestivum L.)-field pea (Pisum sativum L.)-canola (Brassica napus L.)-wheat crop rotation at five sites in the Canadian prairies. The glyphosate rates were 0, 1, 2, 4 and 8 kg ae ha-1, applied pre-seeding and post-harvest every year. The wheat rhizosphere was sampled in the final year of the study and analysed for microbial biomass C (MBC), the composition and diversity of the microbiome, and activities of ß-glucosidase, N-acetyl-ß-glucosiminidase, acid phosphomonoesterase and arylsulphatase. Glyphosate did not affect MBC, the composition and diversity of prokaryotes and fungi, and the activities of three of the four enzymes measured in the wheat rhizosphere. The one effect of glyphosate was a wave-like response of N-acetyl-ß-glucosaminidase activity with increasing application rates. The experimental sites had much greater effects, driven by soil pH and organic C, on the soil microbiome composition and enzyme activities than glyphosate. Soil pH was positively correlated with the relative abundance of Acidobacteriota but negatively correlated with that of Actinobacteriota and Basidiomycota. Soil organic C was positively correlated with the relative abundances of Proteobacteriota and Verrucomicrobiota, but negatively correlated with the relative abundance of Crenachaeota. The activity of acid phosphomonoesterase declined with increasing relative abundance of Acidobacteriota, but increased with that of Actinobacteriota and Basidiomycota. The activity of N-acetyl-ß-glucosaminidase also increased with increasing relative abundance of Actinobacteriota but decreased with that of Mortierellomycota. ß-glucosidase activity also decreased with increasing relative abundance of Mortierellomycota. The core fungal species observed in at least 90% of the samples were Humicola nigrescens, Gibberella tricincta and Giberella fujikuroi. Therefore, this multi-site study on the Canadian prairies revealed no significant effects of 4-year applications of glyphosate applied at different rates on most soil microbial properties despite differences in the properties among sites. However, it is important to keep evaluating glyphosate effects on the soil microbiome and its functioning because it is the most widely used herbicide worldwide.

Wheat and Cereal Rye Inter-Row Living Mulches Interfere with Early Season Weeds in Soybean.

Rapid growth of cool-season weeds in the spring exacerbates weed interference during early soybean (Glycine max (L.) Merr.) establishment in northern climates. This study tested the utility of spring-seeded inter-row living mulches in soybean for early season weed suppression using volunteer canola (Brassica napus L.) as a representative model weed species. The effects of the presence or absence of spring wheat (Triticum aestivum L.) or winter cereal rye (Secale cereale L.) living mulches (mulch type) that had been seeded simultaneously with soybean grown using 38 or 76 cm row spacing (spatial arrangement) and the presence or absence of herbicides used for mid-season mulch termination (herbicide regime) were evaluated in three environments in Manitoba, Canada, in 2013 and 2014. Soybean yield was similar in the presence and absence of the living mulches. In the environment that received the lowest precipitation (Carman 2013), the mulches terminated with post-emergence glyphosate resulted in a 55% greater soybean yield compared to the mulches that remained live throughout the growing season. Inter-row mulches that had been living or terminated mid-season reduced volunteer canola seed production by about one-third (up to 9000 seeds m-2). This study demonstrates the utility of wheat or cereal rye inter-row living mulches for enhanced interference with weeds during early soybean establishment.

Burial Environment Drives Seed Mortality of Kochia (Bassia scoparia), Wild Oat (Avena fatua), and Volunteer Canola (Brassica napus) Irrespective of Crop Species.

Models of weed population demography are critical to understanding the long-term viability of management strategies. The driving factors of weed seedbank persistence are often underrepresented in demographic models due to the cumbersome nature of seedbank research. Simplification of weed seedbank dynamics may induce substantial error in model simulations. A soil bioassay was conducted to determine whether growth of different crop species, including wheat (Triticum aestivum L.), canola (Brassica napus L.), and field pea (Pisum sativum L.), differentially impact seed mortality of kochia [Bassia scoparia (L.) A.J. Scott], wild oat (Avena fatua L.), and volunteer canola in seven burial environments in western Canada. Weed seed survival after the 7 week burial period varied widely among burial environments (from 8% to 88% when averaged among weed and crop species), whereas growth of the different crop species had negligible impact on seedbank persistence. Among environments, wild oat seed survived the greatest (79%), followed by kochia (20%), and volunteer canola (6%). Weed seed survival was associated with soil physical properties (texture) and seed microsite characteristics (temperature), but not crop species or soil chemical properties. Overall, these data support the need for greater integration of soil and environmental parameters into models of weed population demography.

qPCR assay targeting Bradyrhizobium japonicum shows that row spacing and soybean density affects Bradyrhizobium population.

The ability for a soybean plant to be efficiently nodulated when grown as a crop is dependent on the number of effective Bradyrhizobium japonicum that can be found in close proximity to the developing seedling shortly after planting. In Manitoba, the growing of soybean as a crop has increased from less than 500 000 acres in 2008 to over 2.3 million acres in 2017. Since the large increase in soybean production is relatively recent, populations of B. japonicum have not yet developed. In response to this, we developed a primer pair that can identify B. japonicum, and be used to determine the titre found in field soil. Their utility was demonstrated by being used to determine whether row spacing of soybean affects B. japonicum populations, as well as to follow B. japonicum populations in a soybean field over the course of a field season. The data show that plant density can affect B. japonicum populations. Moreover, evidence is presented that suggests plant development affects overall B. japonicum populations.

A Systematic Review of Durum Wheat: Enhancing Production Systems by Exploring Genotype, Environment, and Management (G × E × M) Synergies.

According to the UN-FAO, agricultural production must increase by 50% by 2050 to meet global demand for food. This goal can be accomplished, in part, by the development of improved cultivars coupled with modern best management practices. Overall, wheat production on farms will have to increase significantly to meet future demand, and in the face of a changing climate that poses risk to even current rates of production. Durum wheat [Triticum turgidum L. ssp. durum (Desf.)] is used largely for pasta, couscous and bulgur production. Durum producers face a range of factors spanning abiotic (frost damage, drought, and sprouting) and biotic (weed, disease, and insect pests) stresses that impact yields and quality specifications desired by export market end-users. Serious biotic threats include Fusarium head blight (FHB) and weed pest pressures, which have increased as a result of herbicide resistance. While genetic progress for yield and quality is on pace with common wheat (Triticum aestivum L.), development of resistant durum cultivars to FHB is still lagging. Thus, successful biotic and abiotic threat mitigation are ideal case studies in Genotype (G) × Environment (E) × Management (M) interactions where superior cultivars (G) are grown in at-risk regions (E) and require unique approaches to management (M) for sustainable durum production. Transformational approaches to research are needed in order for agronomists, breeders and durum producers to overcome production constraints. Designing robust agronomic systems for durum demands scientific creativity and foresight based on a deep understanding of constitutive components and their innumerable interactions with each other and the environment. This encompasses development of durum production systems that suit specific agro-ecozones and close the yield gap between genetic potential and on-farm achieved yield. Advances in individual technologies (e.g., genetic improvements, new pesticides, seeding technologies) are of little benefit until they are melded into resilient G × E × M systems that will flourish in the field under unpredictable conditions of prairie farmlands. We explore how recent genetic progress and selected management innovations can lead to a resilient and transformative durum production system.