Evolved polygenic herbicide resistance in Lolium rigidum by low-dose herbicide selection within standing genetic variation

The interaction between environment and genetic traits under selection is the basis of evolution. In this study, we have investigated the genetic basis of herbicide resistance in a highly characterized initially herbicide-susceptible Lolium rigidum population recurrently selected with low (below recommended label) doses of the herbicide diclofop-methyl. We report the variability in herbicide resistance levels observed in F1 families and the segregation of resistance observed in F2 and back-cross (BC) families. The selected herbicide resistance phenotypic trait(s) appear to be under complex polygenic control. The estimation of the effective minimum number of genes (NE), depending on the herbicide dose used, reveals at least three resistance genes had been enriched. A joint scaling test indicates that an additive-dominance model best explains gene interactions in parental, F1, F2 and BC families. The Mendelian study of six F2 and two BC segregating families confirmed involvement of more than one resistance gene. Cross-pollinated L. rigidum under selection at low herbicide dose can rapidly evolve polygenic broad-spectrum herbicide resistance by quantitative accumulation of additive genes of small effect. This can be minimized by using herbicides at the recommended dose which causes high mortality acting outside the normal range of phenotypic variation for herbicide susceptibility

Mechanical and Chemical Control of Smooth Cordgrass in Waillapa Bay, Washington

We evaluated four methods to control smooth cordgrass (Spartina alterniflora Loisel), hereafter spartina, in Willapa Bay, Washington: mowing, mowing plus herbicide combination, herbicide only for clones, and aerial application of herbicide for meadows. (PDF has 7 pages.

Fitness costs associated with evolved herbicide resistance alleles in plants

Predictions based on evolutionary theory suggest that the adaptive value of evolved herbicide resistance alleles may be compromised by the existence of fitness costs. There have been many studies quantifying the fitness costs associated with novel herbicide resistance alleles, reflecting the importance of fitness costs in determining the evolutionary dynamics of resistance. However, many of these studies have incorrectly defined resistance or used inappropriate plant material and methods to measure fitness. This review has two major objectives. First, to propose a methodological framework that establishes experimental criteria to unequivocally evaluate fitness costs. Second, to present a comprehensive analysis of the literature on fitness costs associated with herbicide resistance alleles. This analysis reveals unquestionable evidence that some herbicide resistance alleles are associated with pleiotropic effects that result in plant fitness costs. Observed costs are evident from herbicide resistance-endowing amino acid substitutions in proteins involved in amino acid, fatty acid, auxin and cellulose biosynthesis, as well as enzymes involved in herbicide metabolism. However, these resistance fitness costs are not universal and their expression depends on particular plant alleles and mutations. The findings of this review are discussed within the context of the plant defence trade-off theory and herbicide resistance evolution

FARM-LEVEL EFFECTS OF ADOPTING HERBICIDE-TOLERANT SOYBEANS IN THE U.S.A.

This paper estimates the on-farm impacts of adopting herbicide-tolerant soybean on herbicide use, yields, and farm profits, using an econometric model that corrects for self-selection and simultaneity and is consistent with profit maximization. The model is estimated using nationwide farm-level survey data for 1997. Given that the use of herbicide-tolerant soybeans involves the substitution of a particular herbicide - primarily glyphosate - for other herbicides, we explicitly consider this substitution process in the model.Genetically engineered soybeans, herbicide tolerance, herbicide use, farm profits, technology adoption, yields, Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

Field Evaluation of Herbicides on Vegetables and Small Fruits 2004

Herbicide evaluation studies on vegetables and small fruits were conducted in 2004 at the Arkansas Agricultural Experiment Station at Fayetteville, AR, in an effort to evaluate new herbicides, herbicide mixtures, and their application timings for weed control efficacy and crop tolerance. Results of these studies, in part, provide useful information to producers, fellow researchers, the Crop Protection Industry, and the IR-4 Minor Crop Pest Management Program in the development of potential new herbicide uses in vegetable, and fruit

Horseweed (Marestail) Resistance

Horseweed has documented resistance to EPSPS inhibitors, PSII inhibitors, ALS inhibitors, and PSI inhibitor (Heap, 2018). Glyphosate resistant horseweed moves the herbicide into a vacuole preventing the herbicide from damaging the plant (Ge, 2010). The objective of the this experiment was to determine if nine different horseweed populations were resistant or not to six different herbicide. Experimental design was a randomized complete block with six herbicides, nine locations, and five replications. Heights were recorded for each population before spraying. Each herbicide was sprayed on October 5, 2018, and rates were paraquat (840 g ai/ha), glyphosate (1260 g ae/ha), glufosinate (738 g ai/ha), Atrazine (560 g ai/ha), chlorimuron (13.1 g ai/ha), and dicamba (560 g ai/ha). Horseweed showed the most resistance to atrazine and glyphosate across all locations, and paraquat in some locations. No herbicide had total control fourteen days after spraying. Dicamba had the greatest control of horseweed across all nine locations. Resistance was difficult to identify because horseweed plants were too mature to effectively be control

Adoption of No-Tillage Practices, Other Conservation-Tillage Practices and Herbicide-Resistant Cotton Seed, and Their Synergistic Environmental Impacts

If adoption of herbicide-resistant seed and adoption of conservation-tillage practices are determined simultaneously, adoption of herbicide-resistant seed could indirectly reduce soil erosion and adoption of conservation-tillage practices could indirectly reduce residual herbicide use and increase farm profits. Our objective was to evaluate the relationship between these technologies for Tennessee cotton production. Evidence from simultaneous estimation of a trinomial logit model for adoption of no-tillage, other conservation-tillage, and conventional-tillage practices and a binomial logit model for adoption of herbicide-resistant and conventional cotton seed suggests a simultaneous relationship. The elasticity for acreage in herbicide-resistant seed with respect to the probability of adopting conservation-tillage practices was 3.98. The elasticities for acreages in no-tillage practices and other conservation-tillage practices with respect to the probability of adopting herbicide-resistant cotton seed were 0.34 and 0.10, respectively. Adoption of herbicide-resistant cotton seed in Tennessee reduced soil erosion by 9.2 million tons through its effects on adoption of conservation-tillage practices. By 2004, increases in adoption of conservation-tillage practices increased adoption of herbicide-resistant cotton seed by 445 thousand acres, substituting non-residual herbicides for residual herbicides on those cotton acres.Environmental Economics and Policy,

Evidence for an ecological cost of enhanced herbicide metabolism in Lolium rigidum

1. In some cases, evaluation of resource competitive interactions between herbicide resistant vs. susceptible weed ecotypes provides evidence for the expression of fitness costs associated with evolved herbicide-resistant gene traits. Such fitness costs impact in the ecology and evolutionary trajectory of resistant populations. 2. Neighbourhood experiments were performed to quantify competitive effects and responses between herbicide-susceptible (S) and resistant (R) Lolium rigidum individuals in which resistance is due to enhanced herbicide metabolism mediated by cytochrome P450. 3. In two-way competitive interactions between the S and R phenotypes, individuals of the S phenotype were the stronger effect competitors on both a per capita and per unit-size basis. The S phenotype also exhibited a stronger competitive response to wheat plants than did the R phenotype, displaying significantly greater (30%) above-ground biomass at the vegetative stage. When subjected to competition from wheat, R individuals produced significantly fewer reproductive tillers and allocated fewer resources to reproductive traits than individuals of the S phenotype. 4. The role of potential mechanisms underlying this resistance cost driven by traits such as plant size and tolerance to low resource availability, as well as the evolutionary implications of the results are discussed. 5. Synthesis. Evolved herbicide resistance due to enhanced-herbicide metabolism mediated by cytochrome-P450 in L. rigidum has been shown to be accompanied with an impaired ability to compete for resources. These results are consistent with the resource-based theory that predicts a negative trade-off between growth and plant defence

The Benefits and Beneficiaries of "Public" Investment in Herbicide Use Research and Development

The allocation of benefits from research and development of new herbicide uses is dependent on patent status. The agricultural chemical industry will preferentially invest in herbicide R&D that increases the use of on-patent herbicides from which a company can capture a price premium. The distribution of benefits from increased use of on-patent herbicide will alter over time, with grain growers benefiting at the expense of agrichemical companies once the patent expires. Public sector investment in herbicide R&D may also benefit the agrichemical industry. The size and allocation of the benefits from R&D into on-patent herbicides is analyzed using economic surplus techniques. Two case studies are examined. One involves research into the choice and application of herbicide for new wheat varieties. The second case study involves returns from R&D investment in research into an alternative for the commonly used off-patent herbicide trifluralin. The results from the case studies show that herbicide patent status may not have important implications for "public" R&D investment decisions.Research and Development/Tech Change/Emerging Technologies, Q16, Q18, Q28,