Impacts of a sub-lethal dose of glyphosate on water hyacinth nutrients and its indirect effects on Neochetina weevils

A sub-lethal dose of a herbicide under field conditions was applied to determine if it stimulates an increase in water hyacinth nutrients, thereby increasing feeding intensity by Neochetina spp. weevils used as biocontrol agents of the weed. Nitrogen (N) and carbon (C) were measured and compared between sprayed plants and control plants. At one site (Delta Park), N levels were lower in the sprayed plants compared to the control plants both in the leaves and the crown. At the second site (Farm Dam), leaf N was also lower in the sprayed plants than in the control plants, while no difference was found in crown N. Mean number of feeding scars per cm² at Delta Park was significantly higher on the sprayed plants compared to the control plants, while no significant difference was found at Farm Dam. At Delta Park, there was no correlation, however, between the number of weevil feeding scars and leaf N or C:N ratio in sprayed plants. In conclusion, the sub-lethal dose of glyphosate did not directly result in an increase in weevil feeding intensity but it can be recommended in an integrated control system to retard water hyacinth growth while conserving the weevil population.     

Occurrence and metabolism of sphagnum acid in the cell walls of bryophytes

Sphagnum acid was detected in all 30 Sphagnum species investigated. The content declines in older stem segments. Investigations have so far failed to detect this cinnamic acid derivative outside the Sphagnales. In all the Sphagnum species analysed, a second, conspicuous substance was detected, apparently identical with a degradation product of sphagnum acid produced by enzymatic reaction with peroxidase in vitro. A casual correlation between the sphagnum acid content and peroxidase activity in vivo is discussed. Glyphosate (0.5 mM) inhibits the synthesis of sphagnum acid and shikimate accumulates. Exogenously supplied phenylalanine is able to produce up to 65% reversal of the glyphosate-mediated inhibition of sphagnum acid synthesis. A mixed effect of glyphosate was found on amino acid levels. The content of sphagnum acid is also reduced by daily application of 0.1 mM l-α-aminooxy-β-phenylpropionic acid.     

Residual herbicide treatments reduce Andropogon gayanus (Gamba Grass) recruitment for mine site restoration in northern Australia

Weed invasion is a major threat to Australian tropical savannas, and controlling weeds is essential for successful re‐establishment of native species on disturbed sites. Gamba Grass (Andropogon gayanus) is an African grass which has invaded large areas of tropical savanna across northern Australia. Current management strategies in northern Australia focus on fire and glyphosate to effectively control mature plants; however, re‐establishment of infestations from the soil seed bank remains a major challenge to eradication efforts. This study focused on the effects of soil seed bank treatments on Gamba Grass recruitment on a mine site in northern Australia. Adult Gamba Grass plants within test plots were killed with glyphosate to exclude resource competition. Chemical, physical and biological treatments were then applied, and the treatment effects on subsequent Gamba Grass seedling emergence and survival quantified. Seedling emergence was significantly reduced by three of the four residual herbicide treatments tested. The most effective herbicide treatments, dalapon and sulfometuron, reduced emergence by 90% compared to the standard glyphosate treatment alone. This equated to a reduction in Gamba Grass seedling emergence from 1 seedling/m² to 1 seedling 10 m^?2, a major improvement for Gamba Grass management. These residual herbicide treatments significantly reduced the population density of Gamba Grass for at least 5 months after emergence. The physical and biological treatments did not have a significant effect on seedling emergence. This significant reduction in Gamba Grass seedling emergence and survival can substantially improve Gamba Grass management. Reducing re‐colonisation from the soil seed bank using residual herbicides provides a valuable management tool for land managers, integrating readily with established strategies for controlling the mature plants.     

An individual‐based model of seed‐ and rhizome‐propagated perennial plant species and sustainable management of Sorghum halepense in soybean production systems in Argentina

Perennial plants which propagate through both seeds and rhizomes are common in agricultural and nonagricultural systems. Due to their multifaceted life cycle, few population models are available for studying such species. We constructed a novel individual‐based model to examine the effects of ecological, evolutionary, and anthropogenic factors on the population dynamics of perennial species. To exemplify the application of the model, we presented a case study of an important weed, Sorghum halepense (L.) Pers. (Johnsongrass), in soybean productions in Argentina. The model encompasses a full perennial weed life cycle with both sexual (seeds) and asexual (rhizomes) propagations. The evolution of herbicide resistance was modeled based on either single genes or quantitative effects. Field experiments were conducted in the species' native environment in Argentina to parameterize the model. Simulation results showed that resistance conferred by single‐gene mutations was predominantly affected by the initial frequency of resistance alleles and the associated fitness cost. Population dynamics were influenced by evolved resistance, soil tillage, and rhizome fecundity. Despite the pivotal role of rhizomes in driving the population dynamics of Johnsongrass, most herbicides target the aboveground biomass, and chemical solutions to control rhizomes are still very limited. To maintain effective (short‐term) and sustainable (long‐term) weed management, it is recommended to combine soil tillage with herbicide applications for suppressing the rhizomes and delaying the evolution of resistance. This novel model of seed‐ and rhizome‐propagated plants will also be a useful tool for studying the evolutionary processes of other perennial weeds, cash crops, and invasive species.     

Herbicide treatment alters the effects of water hyacinth on larval mosquito abundance

Invasive aquatic weeds are managed with herbicides to reduce their negative impacts on waterways in many areas, including the California Delta Region. Herbicides create a dynamic environment of living and decomposing plant matter that could affect larval mosquitoes and other invertebrates, such as their predators and competitors. Our objective was to compare the number of larval mosquitoes in water or water hyacinth, before and after an herbicide treatment. We created replicated pond mesocosms with water hyacinth, water hyacinth treated with glyphosate and an oil adjuvant, open water, and water with glyphosate plus adjuvant. We sampled for larval mosquitoes and other aquatic invertebrates. Before herbicide addition, there was a trend for more larval mosquitoes in open water tanks than in tanks with water hyacinth. Herbicide application resulted in an immediate decrease of larval mosquitoes. As decay progressed, larval mosquitoes became most abundant in mesocosms with herbicide‐treated hyacinth and very few larval mosquitoes were found in other habitat treatments. Although the numbers of predatory and competitor insects had some variation between treatments, no clear pattern emerged. This information on how invasive weed management with herbicides affects larval mosquitoes will allow control practices for larval mosquitoes and invasive weeds to be better integrated.     

Isolation and characterization of endophytic bacteria from soybean (Glycine max) grown in soil treated with glyphosate herbicide

Endophytic bacteria are ubiquitous in most plant species influencing the host fitness by disease suppression, contaminant degradation, and plant growth promotion. This endophytic bacterial community may be affected by crop management such as the use of chemical compounds. For instance, application of glyphosate herbicide is common mainly due to the use of glyphosate-resistant transgenic plants. In this case, the bacterial equilibrium in plant–endophyte interaction could be shifted because some microbial groups are able to use glyphosate as a source of energy and nutrients, whereas this herbicide may be toxic to other groups. Therefore, the aim of this work was to study cultivable and noncultivable endophytic bacterial populations from soybean (Glycine max) plants cultivated in soil with and without glyphosate application (pre-planting). The cultivable endophytic bacterial community recovered from soybean leaves, stems, and roots included Acinetobacter calcoaceticus, A. junii, Burkholderiasp., B. gladioli, Enterobacter sakazaki, Klebsiella pneumoniae, Pseudomonas oryzihabitans, P. straminea, Ralstonia pickettii,and Sphingomonassp. The DGGE (Denaturing Gradient Gel Electrophoresis) analysis from soybean roots revealed some groups not observed by isolation that were exclusive for plants cultivated in soil with pre-planting glyphosate application, such as Herbaspirillum sp., and other groups in plants that were cultivated in soil without glyphosate, such as Xanthomonas sp. and Stenotrophomonas maltophilia. Furthermore, only two bacterial species were recovered from soybean plants by glyphosate enrichment isolation. They were Pseudomonas oryzihabitans and Burkholderia gladioliwhich showed different sensibility profiles to the glyphosate. These results suggest that the application at pre-planting of the glyphosate herbicide may interfere with the endophytic bacterial communitys equilibrium. This community is composed of different species with the capacity for plant growth promotion and biological control that may be affected. However, the evaluation of this treatment in plant production should be carried out by long-term experiments in field conditions.     

草甘膦对叶绿体能量转换的影响

除草剂草甘膦抑制植物叶绿体光合磷酸化活力,促进希尔反应活力,表现出明显的解偶联效应。它对叶绿体膜上腺三磷酶(ATPase)活力也起抑制效应,说明ATP合成被抑制不是由ATP酶活力变化所引起。这种解偶联现象主要是因光下质子转移受到抑制,在较低浓度的草甘膦影响下,先抑制质醌转移的质子进入膜内腔,浓度增加到20 mM,对水释放质子也有抑制。所以草甘膦对叶绿体能量转换的影响主要反映在质子转移被抑制,引起磷酸化活力受抑制。