Weak population differentiation and high diversity in Salsola tragus in the inland Pacific Northwest, USA.

BACKGROUND: Salsola tragus is a widespread and problematic weed of semi-arid wheat production globally, and in the inland Pacific Northwest region of the USA. The species exhibits high levels of phenotypic diversity across its range and, at least in California USA, previous work has described cryptic diversity comprising a multi-species complex. Such cryptic diversity could suggest the potential for a differential response to management inputs between groups, and have important implications for the spread of herbicide resistance or other adaptive traits within populations. We used a genotyping-by-sequencing approach to characterize the population structure of S. tragus in the inland Pacific Northwest. RESULTS: Our results indicated that the population in this region is comprised of a single, tetraploid species (S. tragus sensu latu) with weak population structure on a regional scale. Isolation-by-distance appears to be the primary pattern of structure, but an independent set of weakly differentiated clusters of unknown origin were also apparent, along with a mixed mating system and high levels of largely unstructured genetic diversity. CONCLUSIONS: Despite considerable phenotypic variability within S. tragus in the region, agronomic weed managers can likely consider it as a single entity across the region, rather than a collection of cryptic subgroups with possible differential responses to management inputs or agroecosystem conditions. A lack of strong barriers to migration and gene flow mean that adaptive traits, such as herbicide resistance, can be expected to spread rapidly through populations across the region. © 2022 Society of Chemical Industry.

Toward a Better Understanding of Genotype × Environment × Management Interactions-A Global Wheat Initiative Agronomic Research Strategy.

The Wheat Initiative (WI) and the WI Expert Working Group (EWG) for Agronomy (www.wheatinitiative.org) were formed with a collective goal to "coordinate global wheat research efforts to increase wheat production, quality, and sustainability to advance food security and safety under changing climate conditions." The Agronomy EWG is responsive to the WI's research need, "A knowledge exchange strategy to ensure uptake of innovations on farm and to update scientists on changing field realities." The Agronomy EWG aims to consolidate global expertise for agronomy with a focus on wheat production systems. The overarching approach is to develop and adopt a systems-agronomy framework relevant to any wheat production system. It first establishes the scale of current yield gaps, identifies defensible benchmarks, and takes a holistic approach to understand and overcome exploitable yield gaps to complement genetic increases in potential yield. New opportunities to increase productivity will be sought by exploiting future Genotype × Environment × Management synergies in different wheat systems. To identify research gaps and opportunities for collaboration among different wheat producing regions, the EWG compiled a comprehensive database of currently funded wheat agronomy research (n = 782) in countries representing a large proportion of the wheat grown in the world. The yield gap analysis and research database positions the EWG to influence priorities for wheat agronomy research in member countries that would facilitate collaborations, minimize duplication, and maximize the global impact on wheat production systems. This paper outlines a vision for a global WI agronomic research strategy and discusses activities to date. The focus of the WI-EWG is to transform the agronomic research approach in wheat cropping systems, which will be applicable to other crop species.

Opportunities and challenges for harvest weed seed control in global cropping systems.

The opportunity to target weed seeds during grain harvest was established many decades ago following the introduction of mechanical harvesting and the recognition of high weed-seed retention levels at crop maturity; however, this opportunity remained largely neglected until more recently. The introduction and adoption of harvest weed seed control (HWSC) systems in Australia has been in response to widespread occurrence of herbicide-resistant weed populations. With diminishing herbicide resources and the need to maintain highly productive reduced tillage and stubble-retention practices, growers began to develop systems that targeted weed seeds during crop harvest. Research and development efforts over the past two decades have established the efficacy of HWSC systems in Australian cropping systems, where widespread adoption is now occurring. With similarly dramatic herbicide resistance issues now present across many of the world's cropping regions, it is timely for HWSC systems to be considered for inclusion in weed-management programs in these areas. This review describes HWSC systems and establishing the potential for this approach to weed control in several cropping regions. As observed in Australia, the inclusion of HWSC systems can reduce weed populations substantially reducing the potential for weed adaptation and resistance evolution. © 2017 Society of Chemical Industry.