The establishment of Taraxacum officinale plants in grassland

Factors involved in the establishment of Taraxacum officinale (dandelion) seedlings in grasslands and plant mortality in the first growing season were studied during 2008–2011. The study was conducted at 11 grassland sites that differed in the quantity of seed rain and the intensity of seedling predation by slugs. In April, of each study year, 10 plots open to the sedimentation of naturally dispersed seeds were established at each site, five plots of which were also sown with 250 T. officinale seeds each. The amount of natural seed rain, slug feeding activity and number of plants in each plot were then recorded at monthly intervals. Seed rain and seedling predation accounted for c. 50% of the variation in seedling establishment. Populations of established seedlings then declined through October, at which point they were at 25% of the original abundance on average. The percentage of plants that survived varied among sites and years. The temporal and spatial variation in T. officinale establishment and survival of young plants was enormous, even within a small area. Predation of seedlings by slugs can effectively prevent the establishment of T. officinale in grassland. This only occurred, however, at slug abundances not acceptable under conditions of public access.     

Behaviour of bentazon as influenced by water and tillage management in rice‐growing conditions

Bentazon is a widely used herbicide in rice agroecosystems that has commonly been found in water resources. To assess how tillage and water regimes affect sorption/desorption, dissipation and leaching of bentazon in Mediterranean rice‐growing conditions, field experiments were carried out using tillage and flooding (TF), tillage and sprinkler irrigation (TS), no‐tillage and sprinkler irrigation (NTS) and long‐term no‐tillage and sprinkler irrigation (NTS7). After 3 years, the K_d values in TS were 2.3, 1.6 and 1.7 times lower than the values in NTS7, NTS and TF respectively. Greater sorption of bentazon was related to higher contents in total organic carbon and, although to a lesser extent, in humic acids and dissolved organic carbon. The persistence of bentazon was significantly greater under anaerobic (half‐life DT₅₀ = 94.1–135 days) than under aerobic (DT₅₀ = 42.4–91.3 days) incubation conditions for all management regimes. Leaching losses of bentazon were reduced from 78 and 74% in TS and TF to 61 and 62% in NTS7 and NTS respectively. The mid‐ and long‐term implementation of sprinkler irrigation in combination with no‐tillage could be considered a management system that is effective at reducing water contamination by bentazon in Mediterranean rice‐growing agroecosystems. © 2017 Society of Chemical Industry     

Effect of distribution and concentration of topically applied neonicotinoid insecticides in buffalograss,Buchloe dactyloides,leaf tissues on the differential mortality of Blissus occiduus under field conditions

BACKGROUND: Neonicotinoid insecticides are generally efficacious against many turfgrass pests, including several important phloem‐feeding insects. However, inconsistencies in control of western chinch bugs, Blissus occiduus, have been documented in field efficacy studies. This research investigated the efficacy of three neonicotinoid insecticides (clothianidin, imidacloprid and thiamethoxam) against B. occiduus in buffalograss under field conditions and detected statistically significant differences in B. occiduus numbers among treatments. A subsequent study documented the relative quantity and degradation rate of these insecticides in buffalograss systemic leaf tissues, using HPLC. RESULTS: Neonicotinoid insecticides initially provided significant reductions in B. occiduus numbers, but mortality diminished over the course of the field studies. Furthermore, while all three neonicotinoids were present in the assayed buffalograss leaf tissues, imidacloprid concentrations were significantly higher than those of clothianidin and thiamethoxam. Over the course of the 28 day study, thiamethoxam concentrations declined 700‐fold, whereas imidacloprid and clothianidin declined only 70‐fold and 60‐fold respectively. CONCLUSIONS: Field studies continued to verify inconsistencies in B. occiduus control with neonicotinoid insecticides. This is the first study to document the relative concentrations of topically applied neonicotinoid insecticides in buffalograss systemic leaf tissues. Copyright © 2012 Society of Chemical Industry     

Allelopathy and the active metabolites of the endophytic fungus,Alternaria J46, from Platycladus orientalis

The endophytic fungus, Alternaria J46, was isolated from the stem of the medicinal plant, Platycladus orientalis. A suspension of Alternaria J46 mycelial segments and the culture filtrates of the fungi exhibited marked seed germination inhibition against the monocot wheat, large crabgrass, bromegrass, rice and barnyardgrass and weak inhibition against the dicot redroot pigweed and morning glory, but it was safe for use on soybean, rape, cucumber, tomato, lettuce and radish crops. It is possible to use J46 culture filtrates in order to prevent monocot weeds in dicot cropland. Three active metabolites were isolated from an extract of the fungus cultures and elucidated as 3‐acetyl‐5‐sec‐butyltetramic acid (1, tenuazonic acid), 3‐acetyl‐5‐iso‐butyltetramic acid (2, vivotoxin II) and cyclo‐(L‐leucyl‐L‐proline) (3). Among these three compounds, compounds 1 and 2 showed significant phytotoxic effects on the seed germination of large crabgrass, while compound 3 exhibited weak activity, and all were safe for lettuce at 100 μg mL^?1. Accordingly, compounds 1 and 2 were the main active metabolites that were responsible for endophytic fungus Alternaria J46's strong seed germination inhibition against monocotyledons.     

Concepts and Direction of Induced Systemic Resistance in Plants and its Application

Resistance to plant disease is often specific and metabolites and receptors contributing to this specificity may have specific structures. However, simple, structurally-unrelated compounds induce systemic resistance in unrelated plants to diverse pathogens including fungi, bacteria and viruses. Both resistance and induced systemic resistance (ISR) are associated with the rapid accumulation of the same structurally unrelated putative defense compounds that have diverse functions. It has been suggested that cultivar (race)-specific resistance is initiated by the specific interaction of a pathogen product (or pathogen induced product) and a plant receptor. However, restricted infection by pathogens can result in ISR and many different compounds can cause ISR. It is thus evident that there are both specific and non-specific routes to the master switch for ISR and there may be more than one master switch. Are reactive oxygen species and free radicals regulating the master switch(es) via both routes? It is also evident there are many switches, other than the master switch. Adding to the complexity of resistance and ISR are the observations that different compounds and pathways may mediate different biochemical resistances. Activation of one of the pathways may antagonize or enhance the activation or effectiveness of another. The review will address these complexities and questions and propose directions of research which require high priority. Factors which encourage and suppress the application of ISR in agriculture will also be addressed.     

Factors affecting seed dormancy and germination of Johnsongrass, Sorghum halepense (L.) Pers.

Seeds of Johnsongrass [Sorghum halepense (L.) Pers.] germinated to higher percentages (20–30% higher) when incubated at 28 and 35° C than at 10 or 22° C. After-ripening was accelerated by dry storage of these seeds at 50°C. Seeds pre-chilled at 6°C for 2–4 weeks followed by incubation at 28°C germinated 40–60%. Light effects on germination were related to incubation temperatures; inhibitory at 22°C; no response at 28°C; and stimulatory at 35°C. Effects of gibberellin A₃ (GA₃) also varied depending on incubation temperature, sodium hypochlorite (NaOCl) immersion and light conditions. Immersion of dry seeds in either 700 mM NaOCl, 900 mM H₂O₂ or concentrated H₂SO₄ before incubation in water was effective in breaking dormancy. This result suggests the modes of action of H₂SO₄ in the termination of dormancy may be similar to those of NaOCl and H₂SO₄ as previously suggested by Hsiao & Quick (1984), that is by modification or scarification of the hull or seed coat membranes, and also by the supply of additional oxygen to the seed.