Manipulating the ecosystem enables management of soilborne pathogen complexes in annual legume forage systems

Studies were undertaken to examine the potential for manipulating the ecosystem by altering forage species composition, intensity of grazing or by adding Rhizobium, to enhance productivity of subterranean clover (Trifolium subterraneum) forages affected by the soilborne pathogens Pythium irregulare and Rhizoctonia solani. Levels of tap and lateral root disease on clover and its productivity were differentially and significantly affected by the relative proportions of clover to annual ryegrass (Lolium rigidum). In the presence of P. irregulare, both tap and lateral root disease decreased as percentage clover composition increased (R² = 0.58, 0.59, respectively); there was no such significant effect in the presence of R. solani (R² = 0.08, 0.18, respectively). Increasing and maintaining high clover content in forage offers a means to both reduce root disease and increase productivity and forage legume stand persistence. With simulated grazing studies, continuous (i.e. intensive) grazing in the presence of P. irregulare resulted in the most severe tap and lateral root disease, poorest nodulation and smallest roots and shoots compared with intermittent grazing. Hence, reducing grazing intensity also offers potential for significantly increasing productivity of root-rot-affected clover forage. For Rhizobium studies, nodulation was reduced in the presence of P. irregulare or R. solani; the extent of this was dependent upon which pathogen and the clover variety. Overall, these different studies highlight significant potential for manipulating the ecosystem to better manage soilborne pathogen complexes and improve productivity and persistence in annual legume forage systems adversely affected by soilborne oomycete and fungal pathogens.     

Glucosinolate aglucones and analogues: insecticidal properties and a QSAR

Naturally occurring aglucones of three glucosinolates (sinigrin, glucotropaeolin, and epi-progoitrin) were tested for fumigation activity against the house fly, Musca domestica, and the lesser grain borer, Rhizopertha dominica. A total of eight natural aglucones were evaluated in the bioassays. Two aglucones of sinigrin showed efficacy against both species which was comparable with that of a commercial fumigant, chloropicrin. None of the aglucones tested was comparable in activity to dichlorvos. Aglucones of glucotropaeolin were also insecticidal, but not to the same level as the sinigrin aglucones. The aglucones of epi-progoitrin were only slightly effective as fumigants. A quantitative structure–activity relationship (QSAR) was developed for synthetic analogues of the sinigrin and glucotropaeolin aglucones. An electronic parameter, σ*, provided the best predictor of activity in R. dominica, whereas a hydrophobicity parameter, π, best predicted activity in M. domestica. © 1998 Society of Chemical Industry     

Mixtures of organic amendments and biochar promote beneficial soil microbiota and affect Fusarium oxysporum f. sp. lactucae,Rhizoctonia solani and Sclerotinia minor disease suppression

The use of soil fumigants and fungicides to control soilborne pathogens is reduced due to awareness of their negative drawbacks. Long-term application of such agrochemicals negatively affects soil microbiota and reduces natural soil suppressiveness. We investigated long-term impacts of biochar and not-pyrogenic organic amendment (OAs: manure, alfalfa straw and glucose), on disease suppression compared with conventional management in three pathosystems: Fusarium oxysporum f. sp. lactucae (FOL)–lettuce, Rhizoctonia solani–tomato and Sclerotinia sclerotiorum–lettuce, by conditioning soil for 2 years. Soil analyses included pH, electrical conductivity, organic carbon, total nitrogen, C:N ratio, N-NO₃⁻, N-NH₄⁺, cation exchange capacity, available phosphorus, Ca²⁺, Mg²⁺, K⁺, Na⁺, fluorescein diacetate (FDA), and total and active limestone. Soil microbiota was characterized by combining BIOLOG EcoPlates with next-generation sequencing of 16S and 18S rRNA genes. Soil amended with OAs generally suppressed disease by S. sclerotiorum and FOL compared to fumigants and synthetic fertilizers. However, the incidence of R. solani infection was lower in soil treated with synthetic fertilizers than soil amended with OAs. EC, pH, C:N, N-NO₃⁻, N-NH₄⁺, FDA and BIOLOG were significantly correlated with disease, depending on pathosystem. Bacterial richness and diversity, presence of some genera like Acidobacteria, Chloracidobacteria, Solibacteres, Anaerolineae, Nitrospira and Deltaproteobacteria were negatively related to disease incidence of FOL and S. sclerotiorum, whereas damping-off caused by R. solani was negatively affected by the presence of Flavobacterium and Chitinofagha. Therefore, we concluded that long-term application of OAs can effectively improve soil suppressiveness and reduce disease incidence against root pathogens, although the effects vary considerably depending upon pathosystem.     

Germination response of Orobanche seeds subjected to conditioning temperature, water potential and growth regulator treatments

Broomrapes (Orobanche spp.) are parasitic weeds that cause significant losses of crop yield. Experiments were conducted to investigate the seed response to the artificial germination stimulant GR₂₄ in three species of Orobanche subjected to preconditioning under various temperatures, water potentials and with plant growth regulators. The highest germination percentages were observed in Orobanche ramosa, Orobanche aegyptiaca and Orobanche minor seeds conditioned at 18°C for 7 days followed by germination stimulation at 18°C. With the increase of the conditioning period (7, 14, 21 and 28 days), the germination percentage of O. ramosa and O. aegyptiaca progressively decreased. When conditioned at −2 MPa, the germination percentage was lower than at 0 and −1 MPa, especially at 13 and 28°C. Orobanche minor seeds could retain relatively high germination if conditioned at 18, 23 or 28°C, even after significantly extended conditioning periods (up to 84 days). GA₃ (30–100 mg L⁻¹), norflurazon and fluridone (10–100 mg L⁻¹), and brassinolide (0.5–1.0 mg L⁻¹) increased seed germination, while 0.01 mg L⁻¹ uniconazole significantly reduced germination rates of all three Orobanche spp. The promotional effects of GA₃ and norflurazon and the inhibitory effect of uniconazole were evident, even when they were treated for 3 days. Germination of Orobanche seeds was much lower when the unconditioned seeds were directly exposed to GR₂₄ at 10⁻⁶ m . This early GR₂₄-induced inhibition was however alleviated or even eliminated by the inclusion of GA₃ or norflurazon (10–50 mg L⁻¹) in the conditioning medium. On the contrary, the inclusion of uniconazole increased the inhibitory effect of GR₂₄, particularly in the case of O. ramosa.     

Characterization of triadimefon sorption in soils using supercritical fluid (SFE) and accelerated solvent (ASE) extraction techniques

Sorption–desorption of the fungicide triadimefon in field‐moist silt loam and sandy loam soils were determined using low‐density supercritical fluid extraction (SFE). The selectivity of SFE enables extraction of triadimefon from the soil water phase only, thus allowing calculation of sorption coefficients (K_d) at field‐moist or unsaturated conditions. Triadimefon sorption was influenced by factors such as soil moisture content and temperature; sorption increased with increased moisture content up to saturation, and decreased with increased temperature. For instance, K_d values for triadimefon on the silt loam and the sandy loam soils at 40 °C and 10% water content were 1.9 and 2.5 ml g⁻¹, respectively, and at 18% water content, 3.3 and 6.4 ml g⁻¹, respectively. Isosteric heats of sorption (ΔH_i) were −42 and −7 kJ mol⁻¹ for the silt loam and sandy loam soils, respectively. Sorption–desorption was also determined using an automated accelerated solvent extraction system (ASE), in which triadimefon was extracted from silt loam soil by 0.01 M CaCl₂. Using the ASE system, which is basically a fast alternative to the batch equilibration system, gave a similar ΔH_i value (−29 kJ mol⁻¹) for the silt loam soil (K_f = 27 µg^{1 − 1/n} ml^1/n g⁻¹). In order to predict transport of pesticides through the soil profile more accurately on the basis of these data, information is needed on sorption as a function of soil water content. © 2000 Society of Chemical Industry     

An integrated approach to the control of Lycoriella solani (Diptera:Sciaridae) during production of the cultivated mushroom (Agaricus bisporus)

Individual and combined effects of light‐trapping, biological and chemical control on Lycoriella solani (Winnertz) populations in experimental mushroom production cubicles were examined. During three weeks following the introduction of recorded numbers of adult L solani into experimental cubicles, light‐traps caught a maximum 74% of flies initially released. However, light‐trapping stimulated adult fly activity and immature stages in the growing substrate throughout the experiment. Consequently, no yield improvements, independently or in combination with biological control agents, were recorded. Incorporation of diazinon (25 mg AI kg⁻¹) to compost following pasteurisation did not significantly reduce subsequent emergence of adult sciarids. Additional drench application of diflubenzuron (1 g AI m⁻²) to the casing layer reduced the number of immature sciarids during the first cropping period by 99% (P < 0.001). However, inclusion of chemical insecticides reduced the mushroom yield during this period by 14% (P < 0.001). Introduction of the predatory mite Hypoaspis miles (Berlese) to the compost during its colonisation by mycelium of Agaricus bisporus (Lange) reduced emergence of adult sciarids by 87% (P < 0.05). Later introduction of H miles at the beginning of the case‐run period was less effective. Application of the parasitic nematode, Steinernema feltiae (Filipjev (=S bibionis Bovien, after Poinar, 1990)) to the compost during its colonisation by mycelium of A bisporus had no immediate effect on sciarid emergence and provided only limited reduction at later crop stages. Similar application immediately after casing reduced sciarid emergence at first flush by 82% (P < 0.05). Irrespective of application time, a formulation of Bacillus thuringiensis (Berliner) var israeliensis had no significant effect on sciarid emergence or mushroom yields at any production stage. © Crown copyright 2000. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.     

Cellulose-decomposing fungi in polder soils and their possible influence on pathogenic fungi

For a study of the colonisation of the IJsselmeerpolders by fungi, attention was fixed on the cellulose-decomposing fungi, since these are considered to represent the more stable part of the mycoflora of soils. If one assumes that in the North East Polder, cultivated for approximately 25 years, the fungal population is approaching stability, the progress of colonisation of the younger polders can be judged by comparison of the number of species found and their frequency.It is shown that the progress of fungal colonisation did not depend only on the time during which a soil has been dry, but also on the use that has been made of it. Of the species known as antagonists of other fungi,Trichoderma spp. provided an increasingly larger proportion of the total population as the soils were further from stability.It is concluded that the increase of fungal antagonists may well be one of the causes of the decline of such parasites asOphiobolus graminis andRhizoctonia solani. Special mention is made ofGliocladium roseum, the parasitism of which towardsR. solani could be demonstrated in paired cultures.     

Effects of isolate virulence and host susceptibility on development of early blight (Alternaria solani) on tomato*

Early blight of tomato (Lycopersicon esculentum) caused by Alternaria solani has the potential to become one of the most serious diseases throughout the tomato‐producing regions of Greece. Controlled environment experiments were conducted to study the virulence of A. solani isolates and the susceptibility of commercial tomato cultivars and hybrids to early blight. The isolates used, derived from naturally infected tomato plants during the period 1997/1998, differed significantly (P>0.05) in the rate of mycelial growth as well as in their ability to sporulate in vitro. No correlation (R²= 0.33) was found between mycelial growth and conidia production. Isolates of A. solani were virulent to young tomato plants (cv. Ace 55VF), although they differed significantly (P>0.05) in the intensity of symptoms produced on leaves, stems, petioles and flowers. Defoliation was linearly related (R²= 0.87) to the percentage of leaf area with symptoms. Twenty‐three tomato cvs. or F₁ hybrids were evaluated for their susceptibility to early blight. The cultivars or hybrids were arbitrarily categorized as immune, highly tolerant, tolerant, moderately tolerant, susceptible and highly susceptible based on a percent disease index range: 0%, 1‐9%, 10‐24%, 25‐49%, 50‐74% and 75% or more respectively. None of the cultivars or hybrids tested was immune or tolerant to A. solani infection.     

Persistence of pyrazosulfuron in rice-field and laboratory soil under Indian tropical conditions

BACKGROUND: Pyrazosulfuron ethyl, a new rice herbicide belonging to the sulfonylurea group, has recently been registered in India for weed control in rice crops. Many field experiments revealed the bioefficacy of this herbicide; however, no information is available on the persistence of this herbicide in paddy soil under Indian tropical conditions. Therefore, a field experiment was undertaken to investigate the fate of pyrazosulfuron ethyl in soil and water of rice fields. Persistence studies were also carried out under laboratory conditions in sterile and non‐sterile soil to evaluate the microbial contribution to degradation. RESULTS: High‐performance liquid chromatography (HPLC) of pyrazosulfuron ethyl gave a single sharp peak at 3.41 min. The instrument detection limit (IDL) for pyrazosulfuron ethyl by HPLC was 0.1 µg mL^?1, with a sensitivity of 2 ng. The estimated method detection limit (EMDL) was 0.001 µg mL^?1 and 0.002 µg g^?1 for water and soil respectively. Two applications at an interval of 10 days gave good weed control. The herbicide residues dissipated faster in water than in soil. In the present study, with a field‐soil pH of 8.2 and an organic matter content of 0.5%, the pyrazosulfuron ethyl residues dissipated with a half‐life of 5.4 and 0.9 days in soil and water respectively. Dissipation followed first‐order kinetics. Under laboratory conditions, degradation of pyrazosulfuron ethyl was faster in non‐sterile soil (t_1/2 = 9.7 days) than in sterile soil (t_1/2 = 16.9 days). CONCLUSION: Pyrazosulfuron ethyl is a short‐lived molecule, and it dissipated rapidly in field soil and water. The faster degradation of pyrazosulfuron in non‐sterile soil than in sterile soil indicated microbial degradation of this herbicide. Copyright © 2012 Society of Chemical Industry     

Virulence of ‘Dickeya solani’ and Dickeya dianthicola biovar‐1 and ‐7 strains on potato (Solanum tuberosum)

Studies were conducted to explain the relative success of ‘Dickeya solani’, a genetic clade of Dickeya biovar 3 and a blackleg‐causing organism that, after recent introduction, has spread rapidly in seed potato production in Europe to the extent that it is now more frequently detected than D. dianthicola. In vitro experiments showed that both species were motile, had comparable siderophore production and pectinolytic activity, and that there was no antagonism between them when growing. Both ‘D. solani’ and biovar 1 and biovar 7 of D. dianthicola rotted tuber tissue when inoculated at a low density of 10³ CFU mL^?1. In an agar overlay assay, D. dianthicola was susceptible to 80% of saprophytic bacteria isolated from tuber extracts, whereas ‘D. solani’ was susceptible to only 31%, suggesting that ‘D. solani’ could be a stronger competitor in the potato ecosystem. In greenhouse experiments at high temperatures (28°C), roots were more rapidly colonized by ‘D. solani’ than by biovar 1 or 7 of D. dianthicola and at 30 days after inoculation higher densities of ‘D. solani’ were found in stolons and progeny tubers. In co‐inoculated plants, fluorescent protein (GFP or DsRed)‐tagged ‘D. solani’ outcompeted D. dianthicola in plants grown from vacuum‐infiltrated tubers. In 3 years of field studies in the Netherlands with D. dianthicola and ‘D. solani’, disease incidence varied greatly annually and with strain. In summary, ‘D. solani’ possesses features which allow more efficient plant colonization than D. dianthicola at high temperatures. In temperate climates, however, tuber infections with ‘D. solani’ will not necessarily result in a higher disease incidence than infections with D. dianthicola, but latent seed infection could be more prevalent.     

Acaricidal activities of the active component of Lycopus lucidus oil and its derivatives against house dust and stored food mites (Arachnida: Acari)

BACKGROUND: Recent studies have focused on materials derived from plant extracts as mite control products against house dust and stored food mites because repeated use of synthetic acaricides had led to resistance and unwanted activities on non‐target organisms. The aim of this study was to evaluate the acaricidal activity of materials derived from Lycopus lucidus against Dermatophagoides farinae, D. pteronyssinus and Tyrophagus putrescentiae. RESULTS: The LD₅₀ values of L. lucidus oil were 2.19, 2.25 and 8.45 µg cm^?2 against D. farinae, D. pteronyssinus and T. putrescentiae. The acaricidal constituent of L. lucidus was isolated by chromatographic techniques and identified as 1‐octen‐3‐ol. In a fumigant method against D. farinae, the acaricidal activity of 1‐octen‐3‐ol (0.25 µg cm^?2) was more toxic than N,N‐diethyl‐m‐toluamide (DEET) (36.84 µg cm^?2), followed by 3,7‐dimethyl‐1‐octen‐3‐ol (0.29 µg cm^?2), 1‐octen‐3‐yl butyrate (2.32 µg cm^?2), 1‐octen‐3‐yl acetate (2.42 µg cm^?2), 3,7‐dimethyl‐1‐octene (9.34 µg cm^?2) and benzyl benzoate (10.02 µg cm^?2). In a filter paper bioassay against D. farinae, 1‐octen‐3‐ol (0.63 µg cm^?2) was more effective than DEET (20.64 µg cm^?2), followed by 3,7‐dimethyl‐1‐octen‐3‐ol (1.09 µg cm^?2). CONCLUSION: 1‐Octen‐3‐ol and 3,7‐dimethyl‐1‐octen‐3‐ol could be useful as natural agents for the management of three mite species. Copyright © 2011 Society of Chemical Industry     

Methyl isothiocyanate volatilization from fields treated with metam‐sodium

Emission of methyl isothiocyanate (MITC) from fields treated with metam‐sodium (sodium N‐methyldithiocarbamate) is a potential environmental and human safety hazard. Concentrations of MITC at three heights above four arable fields were measured following the application of metam‐sodium at a rate of 480 litre ha⁻¹ (166 kg AI ha⁻¹). Two of these fields were treated by injection into a center‐pivot irrigation system (chemigation), while in the other two fields the fumigant was applied through injection directly into the soil. Generally, higher MITC air concentrations were observed above chemigated than above injected fields. Maximum MITC air concentrations were 11.2 and 7.4 µg m⁻³ recorded 10 cm above ground 6–8 h following application and the minimum concentrations were 0.7 and 0.2 µg m⁻³ observed at 200 cm 30–35 h after application above chemigated and injected fields, respectively. The estimated MITC respiratory exposure a worker might encounter during the re‐entry period ranged between 1.37 and 0.03 mg day⁻¹ in chemigated fields and between 0.35 and 0.02 mg day⁻¹ in the injected fields. These results suggest that application of the fumigant through injection reduced MITC volatilization losses in comparison with the chemigation method, thus posing a relatively lower risk of exposure to MITC emissions. © 2000 Society of Chemical Industry     

In vitro and in vivo antifungal activity of synthetic pure isothiocyanates against Sclerotinia sclerotiorum

BACKGROUND: Isothiocyanates (ITCs) released by the enzymatic hydrolysis of glucosinolates in the Brassicaceae are potentially useful for controlling fungal pathogens. In vitro activity of pure ITCs against Sclerotinia sclerotiorum (Lib.) de Bary was studied by adding them to glass filters in petri dishes and dissolving them in the growing media. RESULTS: Methyl, allyl and benzyl ITCs were the most fungitoxic of the compounds in bioassays with S. sclerotiorum isolate Ss31. In the volatile phase, mycelial growth was completely inhibited by these three compounds. Aromatic ITCs were less toxic in the petri dishes but were more toxic than aliphatic ITCs when dissolved in the agar. Benzyl ITC exhibited the highest inhibitory effect on sclerotial germination, with an EC₅₀ value of 75.1 µmol L^?1. Butyl and benzyl ITCs reduced apothecial production of S. sclerotiorum by 92.5% at the highest concentration. In in vivo assay, only allyl and 2‐phenylethyl ITCs reduced disease incidence (by 76.7 and 70% respectively) at low concentrations. CONCLUSION: Sclerotinia sclerotiorum in the soil might be suppressed by the higher concentrations of allyl and benzyl ITCs released from decomposition of Brassica juncea, B. carinata, B. nigra and Sinapis spp. Copyright © 2011 Society of Chemical Industry     

Factors affecting the activity of ethephon in stimulating seed germination of Striga hermonthica (Del.) Benth.

Ethephon (2-chloroethylphosphonic acid), which generates ethylene, stimulated the germination of pre-conditioned seeds of Striga hermonthica when it was added to the alkaline Gezira clay soil at concentrations of 2.5 to 30 mg kg^?1. As little as 5 min contact with treated soil was enough to stimulate germination. Ethephon in soil did not cause germination of unconditioned seeds for periods of up to 12 days and also had an adverse effect on seed germination when such seeds were given a second ethephon exposure after a storage period which was adequate, in untreated soil, to give the necessary pre-conditioning. Ethephon activity persisted in air-dry soil but declined over a 14 day period in moist soil. In the field ethephon at 0.6 to 4.8 kg ha^?1 decreased the number of Striga shoots and increased sorghum height and flowering.     

The mode of action of RH‐1965: a new phenylpyrimidinone bleaching herbicide

RH‐1965 is a new bleaching herbicide which causes newly developing leaf tissue to emerge devoid of photosynthetic pigments. Mode‐of‐action studies revealed that RH‐1965 inhibited the accumulation of both total chlorophyll and β‐carotene. Concomitantly, it induced the accumulation of the β‐carotene precursors, phytoene, phytofluene and, in particular, ξ‐carotene. Inhibition of chlorophyll accumulation by RH‐1965 is attributed to the photo‐oxidative destruction of chlorophyll in the absence of β‐carotene because RH‐1965 blocked chlorophyll accumulation to a greater extent under high light (50–330 µE m⁻² s⁻¹) than under low light (0.8 µE m⁻² s⁻¹) conditions. Radish (Raphanus sativus L) and barnyardgrass (Echinochloa crus‐galli (L) Beauv) were very senstive to RH‐1965. Under high light (330 µE m⁻² s⁻¹), the I₅₀ values for inhibition of chlorophyll accumulation were 0.10 and 0.15 µM , respectively. Wheat (Triticum aestivus L), on the other hand, was much less sensitive to RH‐1965 (I₅₀ = 1.4 µM ). It is concluded that the mode of action of RH‐1965 involves the inhibition of ξ‐carotene desaturation. © 2000 Society of Chemical Industry     

Antagonismus in vivo von fluoreszierenden Pseudomonaden gegenüber Rhizoctonia solani und Pythium aphanidermatum an Gurken und Buschbohnen

Fluoreszierende Pseudomonaden, die sich als Antagonistenin vitro gegenüberRhizoctonia solani undPythium aphanidermatum erwiesen haben, wurden an Gurken und Bohnen auf Antagonismusin vivo untersucht. Die Effizienz der Antagonisten in Auflaufversuchen gegenüberR. solani war niedriger als beiP. aphanidermatum. Die besten Isolate konnten in mitR. solani verseuchter Erde Auflaufraten von 30–40% erzielen, gegenüberP. aphanidermatum dagegen 40–60%. Die Wirkung der Antagonisten zur Verhütung von Spätinfektionen der Pflanzen war deutlich besser. So konnten 16 Isolate eine Schädigung durchR. solani an Bohnen zwischen 90 und 100% reduzieren. An Gurken konnten 12 Isolate eine Schädigung durchP. aphanidermatum auf 70–80% reduzieren.Fluorescent pseudomonads, which showed antagonism in vitro against Rhizoctonia solani and Pythium aphanidermatum, were investigated for antagonism in vivo using bean and cucumber. The efficiency of the antagonists in germination tests against Rhizoctonia solani was lower than against Pythium aphanidermatum. In soil infected with Rhizoctonia solani the germination rates of the seeds remained between 30 and 40%, whereas against Phytium aphanidermatum some Pseudomonas-strains caused germination rates of 40–60%. The preventive effect of the antagonists against fungal infection after the germination was better. 16 isolates reduced the damage caused by Rhizoctonia solani to bean between 90 and 100%. Damage caused by Pythium aphanidermatum to cucumber was reduced by 12 antagonists between 70 and 80%.

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Mit 4 Abbildungen     

Acaricidal activity of triketone analogues derived from Leptospermum scoparium oil against house‐dust and stored‐food mites

BACKGROUND: Various attempts to control the populations of house‐dust and stored‐food mites have been implemented using synthetic chemicals. Although effective, the repeated use of these chemicals has led to resistance owing to the mite's high reproductive potential and short life cycle. Therefore, this study aimed to develop natural acaricides using oils derived from Leptospermum scoparium JR & G Forst., which may affect the overall biological activity of a mite without adverse effects. Results were compared with those from using benzyl benzoate and N,N‐diethyl‐3‐methylbenzamide (DEET). RESULTS: The LD₅₀ values of L. scoparium oil were 0.54, 0.67 and 1.12 µg cm^?2 against Dermatophagoides farinae (Hughes), D. pteronyssinus (Troussart) and Tyrophagus putrescentiae (Schrank) respectively. The active constituent isolated from L. scoparium was identified as leptospermone (6‐isovaleryl‐2,2,4,4‐tetramethyl‐1,3,5‐cyclohexanetrione) by spectroscopic analysis. Based on the LD₅₀ values of leptospermone and its derivatives, the most toxic compound against D. farinae was leptospermone (0.07 µg cm^?2), followed by 2,2,4,4,6,6‐hexamethyl‐1,3,5‐cyclohexanetrione (1.21 µg cm^?2), benzyl benzoate (10.03 µg cm^?2) and DEET (37.12 µg cm^?2). Furthermore, similar results were observed when the leptospermone and its derivatives were tested against D. pteronyssinus and T. putrescentiae. CONCLUSIONS: These results indicate that L. scoparium oil‐derived materials, particularly leptospermone and 2,2,4,4,6,6‐hexamethyl‐1,3,5‐cyclohexanetrione, have potential for development as new agents for the control of three species of mite. Copyright © 2008 Society of Chemical Industry     

Control of morningglory species using Fusarium solani and its extracts

Abstract

Natural products of an isolate of Fusarium solani App. & Wr. NRRL 18883 grown on rice medium were discovered to be phytotoxic to morningglory. This isolate was evaluated for biocontrol potential on morningglory species including ivyleaf [Ipomoea hederacea (L.) Jacq.], multicoloured (I. tricolor Cav.), paimleaf (I. wrightii Gray), pitted (I. lacunosa L.), purple moonflower (I. turbinata Lag.), red (I. coccinea L.), sharppod (I. cordatotriloba Dennstedt), smallflower (Jacquemontia tamnifolia (L.) Griseb], and tall [I. purpurea (L.) Roth] morningglory. When sprayed at a concentration of 10 g fungus‐infested rice per 50 ml of water, this isolate caused phytotoxic damage including necrosis, chlorosis, growth inhibition, and mortality. Deleterious effects were recorded in all species, ranging from necrotic spots to death, depending on the species. Mortality ranged from 0% at 3 weeks for purple moonflower to 89% for smallflower morningglory. Soil‐drench application (10–20 ml fungal material per 150 g soil) caused wilting and death. Root lengths of 7‐ and 10‐day‐old plants were reduced between 19 and 89% by soil‐drench application and 17–84% by spray application. Whole plant length reduction of 7‐ and 10‐day‐old plants ranged from 0 to 96%, and 39 to 96% for soil‐drench and spray applications, respectively. Testing of F. solani on weed and crop species showed that most broadleaved species were sensitive but monocotyledons were immune. Tests of the phytotoxic extract for known phytotoxins such as common trichothecene (deoxynivalenol) and non‐trichothecene compounds (fusaric acid, moniliformin, fumonisins) were negative. This is the first report of the use of F. solani against morningglory.     

Acaricidal properties of piperazine and its derivatives against house‐dust and stored‐food mites

BACKGROUND: Piperazine derivatives possess pharmacological properties, yet the acaricidal activity of these compounds has not been investigated. This study was conducted to evaluate the colour alteration and acaricidal activity of piperazine derivatives against Dermatophagoides spp. and Tyrophagus putrescentiae (Schrank) using filter paper and fumigant methods. RESULTS: In a fumigant bioassay, 1‐phenylpiperazine (7.83 µg cm^?2) against D. farinae (Hughes) was found to be 4.7 times more toxic than DEET (36.84 µg cm^?2), followed by benzyl benzoate (9.72 µg cm^?2), piperazine (11.41 µg cm^?2), 1‐ethoxycarbonylpiperazine (20.14 µg cm^?2) and 1‐(2‐methoxyphenyl)piperazine (22.14 µg cm^?2). In a filter paper bioassay, 1‐(2‐methoxyphenyl)piperazine (3.65 µg cm^?2) was 5.7 times more toxic than DEET (20.64 µg cm^?2), followed by 1‐ethoxycarbonylpiperazine (4.02 µg cm^?2), 1‐phenylpiperazine (4.75 µg cm^?2), benzyl benzoate (7.83 µg cm^?2) and piperazine (10.59 µg cm^?2). Similar results have been exhibited with piperazine derivatives against D. pteronyssinus (Troussart). However, no activity against T. putrescentiae was observed for piperazine derivatives, except for piperazine. CONCLUSIONS: These results indicate that piperazine derivatives may be suitable as vapour‐phase acaricide fumigants owing to their high volatility, acaricidal activity and safety. 1‐Phenylpiperazine was found to be an excellent mite indicator based on the colour change it induced. Taken together, these findings indicate that piperazine derivatives may be used to replace existing problematical acaricides owing to their activity and ability to act as a mite indicator. Copyright © 2009 Society of Chemical Industry     

Influence of environmental factors on seed germination and emergence of Iresine diffusa

Iresine diffusa has become more abundant under no‐till soyabean in Argentina. The influence of temperature, light, cold‐wet storage, osmotic potential, dry storage and depth of seed burial on germination and emergence of I. diffusa was examined in a growth chamber experiment. Iresine diffusa seeds germinated at the highest proportion (>0.80) in all fluctuating day/night temperatures tested. Conversely, under a constant temperature regime, maximum germination rates occurred at 15 (0.78) and 20°C (0.82), and minimum germination rates occurred at 10 (0.19) and 30°C (0.36). Seed germination was not influenced by light exposure. However, germination decreased after 12 (0.76) and 16 (0.65) weeks in cold‐wet storage. To reduce germination significantly, ?0.4 MPa of osmotic potential (induced by PEG‐6000) or 120 mmol L^?1 of salt (NaCl) concentration was required. Seeds of I. diffusa showed high viability (0.85) after 720 days of dry storage. Low emergence was recorded for seeds buried at 2 cm, and seedling emergence was completely inhibited when seeds were buried at 5 and 10 cm. Iresine diffusa seeds had high viability and were capable of emerging in a broad range of environmental conditions. The thermal germination conditions, shallow soil depths and high moisture conditions in germination phase for I. diffusa are congruent with the conditions in Argentina no‐tillage soyabean. Thus, no‐tillage could provide better conditions for germination than conventional tillage systems. However, due to the fact that I. diffusa can reproduce by rhizomes, further research should be conducted to understand the relative importance of the vegetative reproductive strategy in relation to the presence and persistence of this weed in fields.