Evolved resistance to the herbicide glyphosate has been reported in eleven weed species, including Lolium multiflorum. Two glyphosate-resistant L. multiflorum populations were collected, one from Chile (SF) and one from Oregon, USA (OR), and the mechanisms conferring glyphosate resistance were studied. Based on a Petri dish dose-response bioassay, the OR and the SF populations were two and fivefold more resistant to glyphosate when compared to the susceptible (S) population, respectively; however, based on a whole-plant dose-response bioassay, both OR and SF populations were fivefold more resistant to glyphosate than the S population, implying that different resistance mechanisms might be involved. The S population accumulated two and three times more shikimic acid in leaf tissue 96 h after glyphosate application than the resistant OR and SF populations, respectively. There were no differences between the S and the glyphosate-resistant OR and SF populations in 14C-glyphosate leaf uptake; however, the patterns of 14C-glyphosate translocation were significantly different. In the OR population, a greater percentage of 14C-glyphosate absorbed by the plant moved distal to the treated section and accumulated in the tip of the treated leaf. In contrast, in the S and in the SF populations, a greater percentage of 14C-glyphosate moved to non-treated leaves and the stem. cDNA sequence analysis of the EPSP synthase gene indicated that the glyphosate-resistant SF population has a proline 106 to serine amino acid substitution. Here, we report that glyphosate resistance in L. multiflorum is conferred by two different mechanisms, limited translocation (nontarget site-based) and mutation of the EPSP synthase gene (target site-based).
A suspected glyphosate-resistant Italian ryegrass biotype was collected from a filbert orchard near Portland, OR, where glyphosate was applied multiple times per year for about 15 yr. Greenhouse studies were conducted to determine if this biotype was glyphosate resistant. The plants were sprayed with glyphosate (0.01 to 3.37 kg ae ha Ϫ1 ) 14 d after planting and shoot biomass was determined 3 wk after herbicide treatment. Based on the dose-response experiments conducted in the greenhouse, the suspected Italian ryegrass biotype was approximately fivefold more resistant to glyphosate than the susceptible biotype. Plants from both susceptible and resistant biotypes were treated with glyphosate (0.42 and 0.84 kg ha Ϫ1 ) and shikimic acid was extracted 12, 24, 48, and 96 h after treatment. The susceptible biotype accumulated between three and five times more shikimic acid than did the resistant biotype. Leaf segments from both susceptible and resistant biotypes were incubated with different glyphosate concentrations (0.5 to 3000 M) for 14 h under continuous light. Shikimic acid was extracted from each leaf segment and quantified. At a concentration up to 100 M, leaf segments from the susceptible biotype accumulated more shikimic acid than leaf segments from the resistant biotype. The epsps gene was amplified and sequenced in both susceptible and resistant biotypes; however, no amino acid change was found in the resistant biotype. The level of resistance in this biotype is similar to that reported for a glyphosate-resistant Italian ryegrass biotype from Chile.Nomenclature: Glyphosate; Italian ryegrass, Lolium multiflorum Lam. LOLMU; filbert, Corylus avellana L.
Weeds of the genus Orobanche parasitize many dicotyledonous species, causing severe damage to vegetable and field crops worldwide. In Oregon, the number of red clover fields contaminated with small broomrape has increased in recent years. Small broomrape parasitism in red clover is temperature related. In this study, the temperature-dependent relationship was developed into a predictive model based on growing degree-days (GDD) for small broomrape parasitism in red clover. The model was developed in greenhouse studies and validated in the field during three growing seasons. A strong relationship between GDD and parasite size allowed for the creation of a simple predictive model for tubercle number based on GDD. The proposed model is based on a temperature range realistic to western Oregon climatic conditions and predicts lag, log, and maximum phases for four parasitism sizes in relation to GDD. Small broomrape parasitism in red clover began at about 400 GDD, but red clover biomass accumulation was not affected by parasitism before 1,200 GDD. Small broomrape flower stalk emergence began at about 1,100 GDD. Field studies validated that GDD could be a predictive parameter for small broomrape parasitism and could be used to time detection surveys and herbicide applications.
Although discussion of the role of urban agriculture in developing nations has occurred over the past decade, dialogue relating to urban agriculture in industrialized countries, including the United States (US) has only recently begun to attract significant attention. The unique factors that influence urban agriculture, including limited and non-traditional land access, use of reclaimed soils and alternative growing mediums, local legal and political environments, social and community-based missions, and involvement of non-traditional farmers, create a production system distinct from rural agricultural enterprises. In many cases, specific local environmental and external factors drive urban farms to develop unique innovations for space-intensive production systems, often creating a dominant paradigm for urban farming for a given location. Furthermore, non-production-related organizational goals are often the primary focus of urban agricultural operations, with the food production becoming a secondary objective. In order to address this information gap regarding the status of urban agriculture in the US, our project, centered at the University of Wisconsin-Madison, gathered data through site visits to and interviews of organizations in seven cities, examining how structural and strategic food system factors shape urban agricultural efforts. A broad range of operations are considered, including diverse business and production models based on both commercial and community-based management strategies and production in parking and vacant lots, warehouses, public land and peri-urban locations. Based on these observations, the unique innovations in space-intensive agricultural production that have arisen in response to urban food system factors are discussed. We conclude with an assessment of the most significant challenges continuing to face urban agriculture.following: community gardens, commercial gardens, community supported agriculture, farmers' markets, personal gardens, and urban farms'. The focus of this paper will be on agricultural production efforts that are located within, or are closely proximate to, a metropolitan area and strive to produce food to be consumed in the same area. Primary attention will be given to projects producing at the commercial or community level rather than solely for personal household consumption.Urban agriculture integrates a wide variety of production systems, ranging from models familiar to a typical rural farmer to techniques that push the limits of the definition of agriculture. This diversity includes both very high-tech approaches, such as nutrient film technology, and low-tech methods, such as planting into soil-filled recycled buckets. Although many aspects of urban agricultural production are similar to those of small-scale rural farms, several factors set it apart from traditional agricultural operations. Limited and non-traditional land access, use of urban soils and alternative growing media, unique legal and political environments, non-production-related missions and i...
Broomrapes (Orobanche spp.) are chlorophyll-lacking root parasites of many dicotyledonous species and cause severe damage to vegetable and field crops from several botanic families such as Fabaceae, Solanaceae, Compositae, and Umbelliferae. In Oregon, small broomrape has been identified as a parasite of red clover. In Oregon field studies, small broomrape control was excellent when imazamox was applied postemergence to red clover but preemergence to small broomrape. Temperature is one of the main factors that affect broomrape development. The objective of this study was to optimize small broomrape chemical control in red clover based on growing degree days (GDD). The study was conducted in controlled temperature conditions. Red clover plants were grown in soil artificially infested with small broomrape seeds. Imazamox was applied at 800, 1,000, 1,200, and 1,400 GDD. There was no injury to red clover from any imazamox treatment at any of the application timings. Small broomrape shoot emergence was reduced where imazamox was applied compared to the untreated control. Early imazamox applications reduced small broomrape biomass more than later applications. Control was greatest when imazamox was applied at 20 g ai ha−1 at 1,000 GDD. This application controlled small broomrape for 800 GDD after initial treatment. However, season-long control would require an additional treatment. This model predicts the optimal timing and rate of imazamox application for small broomrape control in red clover.
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