The enantiomeric composition of triadimenol produced during metabolism of triadimefon by fungi: III. Relationship with sensitivity to triadimefon

Fifteen species of fungi, grown in shake culture in a liquid nutrient medium containing a 50:50 mixture of the 1R and 1S enantiomers of triadimefon, reduced triadimefon to triadimenol, the extent of reduction varying from <1% to >95% according to species. Each produced its own characteristic pattern of two or more of the four possible enantiomers of triadimenol and the stereoselectivity and stereospecificity of the reduction is discussed. The sensitivity of each fungus to individual enantiomers and a mixture of enantiomers of triadimefon and of triadimenol was assessed. Three broadly defined groups of fungi were found: (i) sensitive to both triadimefon and tridimenol, (ii) insensitive to both, and (iii) insensitive to triadimefon but moderately sensitive to triadimenol. In many cases it was possible to predict, at least semiquantitatively, the sensitivity of an organism to triadimefon from a knowledge of its characteristic metabolism to triadimenol and its sensitivity to the individual triadimenol enantiomers. No evidence for synergism or antagonism was found.     

The enantiomeric composition of triadimenol produced during metabolism of triadimefon by fungi. Part I: Influence of dose and time of incubation

Botrytis cinerea, grown in shake culture in a liquid nutrient medium containing different amounts of triadimefon (4–40 mg litre^?1), produced triadimenol as the sole major metabolite. Analysis by gas-liquid chromatography (g.l.c.) showed the presence of (1R,2S) and (1S,2S)-triadimenol, but no (1S,2R) or (1R,2R)-enantiomer. The proportion of (1R,2S) to (1S,2S)-triadimenol decreased over the period 6 to 168 h and with increased amounts of applied triadimefon. The implications of these patterns of metabolism are discussed in terms of overall fungitoxicity, the stereospecificity of the reduction process and the shortcomings of conventional, non-chiral analysis of diastereoisomers by g.l.c. for assessing the sensitivity of fungi to such fungicides as triadimefon.     

The diastereomeric ratio in the triadimenol produced by fungal metabolism of triadimefon,and its role in fungicidal selectivity

The ratio of the two diastereomeric forms of triadimenol, produced by the reduction of triadimefon in various fungi, was studied. The reduction of triadimefon in fungi seems to be a concentration-dependent process, the virtual irreversibility of which is proved. Not only the degree of triadimefon reduction, but also the ratio of the triadimenol diastereomers produced, was characteristic for each of the fungal species. A direct correlation, between the production of the more active diastereomeric form and the sensitivity of the fungal species to triadimefon, was observed.     

Effect of triadimefon and triadimenol on growth of various plant species as well as on gibberellin content and sterol metabolism in shoots of barley seedlings

The fungicides triadimefon and triadimenol markedly reduced growth of coleoptiles, primary leaves, and roots of barley seedlings when grown for 7 days in petri dishes in the dark. The addition of gibberellins (A₁, A₃, A₄, A₇, A₉) alleviated growth retardation of primary leaves and coleoptiles induced by the fungicides. While fungicide-induced growth retardation of the shoots was partly relieved by kinetin, IAA did not show an alleviating activity. Triadimefon and triadimenol also substantially retarded the elongation of shoots of tomato and cotton plants and simultaneous application of GA₃ nullified the retardation. The fungicides only slightly interfered with both α-amylase production of intact germinating barley seed and the GA₃-induced α-amylase synthesis in barley endosperm. On the other hand, extracts of triadimefon- and triadimenol-treated shoot tissue of 10- to 12-day-old barley plants contained substantially lower gibberellin-like activity than control shoots. Both compounds also interfered in sterol metabolism of shoots of barley seedlings when compared to control plants, treatment resulted in lower amounts and altered proportions of C-4,4-desmethyl sterols. While both fungicides inhibited synthesis of C-4,4-desmethyl sterol fraction, sterols possessing C-4 and C-14-methyl groups were accumulated. It is assumed that triadimefon and triadimenol interfere in gibberellin and sterol biosynthesis in barley seedlings by inhibiting oxidative demethylation reactions.     

The relationship between antifungal diene levels and fungal inhibition during quiescent infection of unripe avocado fruits by Colletotrichum gloeosporioides

Quantitative changes in the antifungal compound, 1-acetoxy-2-hydroxy-4-oxo-heneicosa-12.15-diene, in freshly harvested avocado fruits during the initial stages of fungal development were investigated to determine the possible involvement of the compound in quiescent infections of Colletotrichum gloeosporioides. The concentration of the antifungal compound in the peel decreased to subfungitoxic concentrations 16 h after harvest. Fifty-six hours later the antifungal diene had increased to c . 3800 μg/g fresh weight. At this stage, germinated appressoria had penetrated the cuticle to the epidermal cells but no fungal development was observed until 7 days later when the concentration of the diene had decreased to 100-110μg/g fresh weight. Following a dip treatment at 55°C for 5 or 10 min, the antifungal diene concentration decreased as in the controls, but it remained at subfungitoxic concentrations for a longer period enabling fungal development and early symptom expression.
The concentration of the diene in the flesh of freshly harvested fruit decreased to 120 μg/g fresh weight 24 h after harvest. Inoculation of peeled fruits with spores of C. gloeosporioides showed germination without appressoria formation and symptom expression occurred 24-48 h later. Symptom expression was delayed if fruits were inoculated after coating the flesh with epicuticular wax extracts or if the flesh was inoculated 3 days after harvest when the antifungal diene had regained a fungitoxic concentration. Disease symptoms were expressed in soft fruits containing subfungitoxic concentrations of the diene.
We conclude that the diene in unripe avocado fruits inhibits fungal development of germinated appressoria or conidia. The quiescent structure of C. gloeosporioides in unripe avocado fruit is a subcuticular hypha.     

Differences in the extent of fungal development, host cell necrosis and symptom expression during race-cultivar interactions between Phaseolus vulgaris and Colletotrichum lindemuthianum

The cellular reactions of excised hypocotyl segments of 31 cultivars of Phaseolus vulgaris to infection by two races of Colletotrichum lindemuthianum were surveyed. Consistent differences in the extent of fungal development and host cell necrosis were used to establish six infection categories.
Extreme susceptibility (category 5) involved initial formation of infection vesicles in living epidermal cells and a prolonged period of intracellular biotrophic development prior to necrotrophic growth and production of spreading lesions. Extreme resistance (category 0) involved rapid death and browning of penetrated epidermal cells, without formation of infection vesicles or a detectable biotrophic phase. Fungal growth and host necrosis were limited to single epidermal cells. Intermediate reactions (categories 1 to 4) initially resembled category 5, but after a biotrophic phase of varying duration, infected cells and some adjacent uninfected cells died and became brown, and fungal growth ceased. Symptoms ranged from flecks (small groups of dead cells) to large areas of necrosis (limited lesions). Similar intermediate reactions also occurred in normally susceptible hypocotyls which were transferred from 17 to 25°C, or which retained cotyledons.
The finding that resistance is expressed at different stages of infection is discussed in relation to the regulation of cultivar specificity.     

Studies into the differential activity of the hydroxybenzonitrile herbicides: II. Uptake,movement and metabolism in two contrasting species

Uptake, movement, and metabolism of unformulated ioxynil and bromoxynil salts were investigated in Matricaria inodora and Viola arvensis. The morphology of these two species did not give rise to different spray retention and contact angles. After 7 days, uptake of [¹⁴C]ioxynil-Na reached 8.26% of applied ¹⁴C activity in M. inodora and 16.77% of that in V. arvensis compared with 1.54 and 3.83%, respectively, for [¹⁴C]bromoxynil-K. Over 98% of the ¹⁴C activity detected in the plant after 7 days remained in the treated leaves of V. arvensis following [¹⁴C]ioxynil-Na treatment. However, 8.7% of the ¹⁴C activity detected in [¹⁴C]ioxynil-Na-treated M. inodora was recovered from the apex and developing leaves reflecting a greater translocation. [¹⁴C]Bromoxynil-K was more mobile in both species and after 7 days 87.5 and 91.39% were detected in the treated leaves of M. inodora and V. arvensis, respectively. In both species the majority of translocated ¹⁴C activity was recovered from the apex and developing leaves. Up to 20% of the applied [¹⁴C]ioxynil-Na and [¹⁴C]bromoxynil-K was not detected within the treated plant. Extraction of treated plants revealed no detectable metabolic breakdown of ioxynil-Na to halogenated derivatives in either species. However, metabolic breakdown of bromoxynil-K was apparent in V. arvensis. No significant root exudation was detected when [¹⁴C]ioxynil-Na and [¹⁴C]bromoxynil-K were applied to hydroponically grown S. media and V. arvensis. Losses of ¹⁴C activity were due to herbicide volatility or degradation to volatile products on the leaf surface.     

太白山锐齿栎树干基部两种蚂蚁的筑巢生态学及其蚁巢、体表真菌组成研究(英文)

本文研究了太白山锐齿栎景观林带树干基部筑巢的两种蚂蚁的筑巢生态学及其巢内真菌的组成。研究结果表明:亮腹黑褐蚁Formica gagatoides Ruzsky是锐齿栎林中的优势蚁种,可在地表及树干上活动,主要取食栎树枝条上蚜虫所分泌的蜜露及其他昆虫和植物材料;盘腹蚁Aphaenogaster sp.仅在蚁巢周围活动,捕食其他小型昆虫;亮腹黑褐蚁F.gagatoides蚁巢材料含水量非常高,而盘腹蚁Aphaenogaster sp.的蚁巢较为干燥。锐齿栎林中树干的平均蚁栖率为20.3%,但蚁栖率随海拔差异而不同(海拔1800m的锐齿栎林带蚁栖率仅为6%,海拔1600m的锐齿栎林带蚁栖率高达38.5%)。两种蚂蚁的长期营巢活动造成树干基部腐朽、孔洞不断扩大,严重影响锐齿栎树干的水分、营养传输及生长,且极易倒伏和风折。两种蚂蚁巢内及其体表真菌的种类组成明显不同,从亮腹黑褐蚁F.gagatoides蚁巢材料中可分离出7种真菌,而从盘腹蚁Aphaenogaster sp.巢中仅分离出2种;从亮腹黑褐蚁F.gagatoides体表可分离出4种真菌,而从盘腹蚁Aphaenogaster sp.体表分离到3种真菌;其中Tri...     

Sensitivity among species of Solanaceae to AAL toxins produced by Alternaria alternata f.sp. lycopersici

The necrotrophic fungus Alternaria alternata f.sp. lycopersici produces AAL toxins that cause necrosis in tomato tissues with high specificity. Resistance or susceptibility of tomato to the fungus and insensitivity or sensitivity to AAL toxins are determined by a single locus, Asc . In order to investigate further the specificity of the host–fungus interaction, 200 species of Solanaceae were tested for their sensitivity to AAL toxins T_A and T_B. Twenty-five species were found to be sensitive to AAL toxins at a concentration of (0·2  µ m ) used for distinguishing sensitive and insensitive tomato plants. Three species were as sensitive as the sensitive tomato line, indicating that AAL toxins effectively act on a broader range of plant species within the Solanaceae.     

Vertical dispersal of plant pathogens by splashing. Part II: experimental study of the relationship between raindrop size and the maximum splash height

This paper describes a simple experimental test of the theoretical relationship between raindrop diameter and maximum splash height proposed by Walklate (1989). This relationship contains two empirical parameters to model the characteristics of a splash target that limits upward movement of splash droplets. These parameters are estimated by fitting the proposed relationship to measurements of the maximum height of splashing from a variety of targets including leaves, straw and water films on horizontal plane surfaces. The experimental technique provides a simple and meaningful way to characterize the behaviour of splashing from plant material. This information can be applied to describe the upward movement of inoculum in crop canopies during rainfall.     

Effects of three esca-associated fungi on Vitis vinifera L.: III. Enzymes produced by the pathogens and their role in fungus-to-plant or in fungus-to-fungus interactions

When the esca-associated fungi Phaeomoniella chlamydospora (Pch), Togninia minima (Tmi) and Fomitiporia mediterranea (Fme) were grown in liquid stationary cultures, it was seen that they were able to live in media containing resveratrol (RES) or tannic acid (TA) as the sole carbon source and that the fungi were able to convert both compounds. Particular attention is paid here to detecting RES and TA conversion. Pch, Tmi and Fme were partially inhibited by RES or TA. Pch, Tmi and Fme produced extracellular tannase, laccase and peroxidase enzymes in liquid or agarized cultures, whether glucose was present or not. When colonies of Pch, Tmi and Fme were confronted, they showed spatially and temporally heterogeneous patterns of laccase and peroxidase activity. The results indicate the non-synergistic, competitive association of Pch and Tmi and the inhibition of Fme growth. Muconic acid, a well-known intermediate in a large number of lignin and phenol oxidative processes, can partly or completely inhibit the lignolytic agent Fme, but is tolerated by Pch and Tmi. An explanation for wood pigmentation patterns by Pch, Tmi and Fme is given.     

The degradation of diflubenzuron and its chief metabolites in soils. Part II: Fate of 4-chlorophenylurea

The fate of 4-chlorophenylurea in soils was studied with two preparations: one labelled with ¹⁴C in the phenyl ring and the other in the carbonyl group. The initial dose of 1 mg kg^?1 decreased to 50% in about 5 weeks in aerobic sandy clay and in about 16 weeks in anaerobic hydrosoil. Soil treatment with each of the preparations resulted in the release of [¹⁴C]carbon dioxide, pointing to decarbonylation and ring opening. The fraction of non-extractable (soil-bound) radioactivity increased during incubation. Quantities of ring-¹⁴C-labelled and carbonyl-¹⁴C-labelled bound residues differed strongly in the aerobic soil but only slightly in the anaerobic hydrosoil. It is assumed that two sorts of bound residues are formed from 4-chlorophenylurea: one is fairly stable and might consist of bound 4-chloroaniline or its transformation products, whereas the other is presumed to be a degradable derivative of 4-chlorophenylurea.     

Action of pesticides on earthworms. Part II: Elimination of parathion by the earthworm Eisenia foetida (Savigny)

The earthworm, Eisenia foetida, eliminated parathion and carbofuran at first order rates when continually rinsed in water after treatment with the pesticides. This experiment was also carried out on Lumbricus rubellus for comparison. Carbofuran which is more soluble in water, was eliminated quicker than parathion. The later rate of elimination was very similar for the two species, but immediately after injection the rate was much higher in E. foetida. The metabolism of 1-ethyl¹⁴C labelled parathion and paraoxon (diethyl 4-nitrophenyl phosphate) was studied in E. foetida. The worm was able to convert parathion to paraoxon by a rather slow process although this metabolite could not be detected in the worms due to its rapid transformation to diethyl hydrogen phosphate. Indirectly, paraoxon can be postulated as a parathion metabolite because of a progressive depression of cholinesterase level observed after treatment with parathion. Small amounts of diethyl hydrogen phosphate were detected as a metabolite of parathion; this is also an indication of paraoxon formation. During the 30 h following injection of parathion, only 4.4% of the applied dose was recovered as water-soluble metabolites (2.8% in the worms and 1.6% in the sand surrounding them), while 52% was recovered as unmetabolised parathion. Because of inefficient injection, only 70-59% of the dose thought to be injected was recovered. Therefore the part of the actual applied dose that remained unmetabolised was probably even greater (88%). Five days after injection of parathion, 15 and 9.3 % of the recovered radioactivity in the surrounding sand and in the worm extracts, respectively, was identified as O,O-diethyl O-hydrogen phosphorothioate, 3.7 and 7.0% as diethyl hydrogen phosphate, 8.8 and 3.3% as O-ethyl O-4-nitrophenyl O-hydrogen phosphorothioate (desethylparathion) and/or O-4-aminophenyl O,O-diethyl phosphorothioate, while 70.3 and 80.4% was unmetabolised parathion. Paraoxon was very quickly hydrolysed to diethyl hydrogen phosphate in vivo and in vitro. The in-vitro hydrolysis was associated with a microsomal fraction and was not inhibited by ethylenediaminetetra-acetic acid or 4-(chloromercuri)benzoic acid, and incompletely by aldicarb. Cholinesterase and arylesterase were therefore excluded as enzymes responsible for the activity.     

The fungicidal activity of substituted 1, 4-naphthoquinones. Part II: Alkoxy,phenoxy and acyloxy derivatives

A representative group of 1, 4-naphthoquinone derivatives, bearing alkoxy, phenoxy and acyloxy substitutents in the 2-position, has been synthesised and assayed against Botrytis cinerea, Cladosporium fulvum and Venturia inaequalis. The alkoxy compounds exhibited moderate activity, which was enhanced by the presence of a 3-chloro and, to a lesser extent, a 3-bromo substituent. 2-Chloro-3-phenoxy derivatives were highly active, but diphenoxy compounds were inactive. Acyloxy derivatives possessed only weak activity unless a halogen atom was present in the 3-position; benzoyloxy compounds, however, were generally poor fungicides.     

Effects of three esca-associated fungi on Vitis vinifera L.: III. Enzymes produced by the pathogens and their role in fungus-to-plant or in fungus-to-fungus interactions

When the esca-associated fungi Phaeomoniella chlamydospora (Pch), Togninia minima (Tmi) and Fomitiporia mediterranea (Fme) were grown in liquid stationary cultures, it was seen that they were able to live in media containing resveratrol (RES) or tannic acid (TA) as the sole carbon source and that the fungi were able to convert both compounds. Particular attention is paid here to detecting RES and TA conversion. Pch, Tmi and Fme were partially inhibited by RES or TA. Pch, Tmi and Fme produced extracellular tannase, laccase and peroxidase enzymes in liquid or agarized cultures, whether glucose was present or not. When colonies of Pch, Tmi and Fme were confronted, they showed spatially and temporally heterogeneous patterns of laccase and peroxidase activity. The results indicate the non-synergistic, competitive association of Pch and Tmi and the inhibition of Fme growth. Muconic acid, a well-known intermediate in a large number of lignin and phenol oxidative processes, can partly or completely inhibit the lignolytic agent Fme, but is tolerated by Pch and Tmi. An explanation for wood pigmentation patterns by Pch, Tmi and Fme is given.     

The kinetics of insecticide action. Part IV: the in-vivo distribution of pyrethroid insecticides during insect poisoning

The distribution of pyrethroids in insects has been studied using a combination of mathematical modelling and experimental observation. This approach has resulted in the formulation of a physiological model of the pharmaco-kinetics of cypermethrin applied topically to larvae of Spodoptera littoralis. Development of this model from simpler two- and three-compartment models is described. Simple models, whilst capable of complex behaviour, consider only the average rates and magnitudes of pharmaco-kinetic processes over whole animals, and cannot account for differences in concentration of insecticide between individual tissues. This can be achieved by using physiological models, but these require more experimental information for their validation. Moreover, unless simplifying assumptions are made, analytical solutions are not feasible for the large number of equations necessary to define such models. The modelling studies prompted an investigation of (1) in-vivo binding of insecticide to insect tissues, (2) the sizes of body compartments, and (3) the factors which affect the distribution of toxicant between these compartments. Binding has a marked effect on pharmacokinetic profiles and may result in oscillatory behaviour. During poisoning, the total bound cypermethrin increases proportionally to the cube root of the elapsed time. This results in a rapid rate of increase over early elapsed times (< 3h) which slows to approach a more linear form thereafter. Average sizes for the body compartments of larvae of Spodoptera littoralis Boisd, and the steady-state distribution of cypermethrin in these compartments are described. Although the haemolymph, which acts as the main distributive phase during poisoning, forms the largest compartment by volume, it has a low affinity for cypermethrin and distribution reaches steady state within 5 min after topical application. The nerve cord (the target tissue), which is the smallest compartment, has the highest steady-state concentration of cypermethrin. The distribution of cypermethrin in larval tissues is related to the ratios of tissue dry matter to water content.     

Effects of three esca-associated fungi on Vitis vinifera L.: IV. Diffusion through the xylem of metabolites produced by two tracheiphilous fungi in the woody tissue of grapevine leads to esca-like symptoms on leaves and berries

Two naphthalenone pentaketides (scytalone and isosclerone) and α-glucans (pullulan) are produced in vitro and in planta by Phaeomoniella chlamydospora (Pch) and Togninia minima (Tmi), two tracheiphilous fungi associated with the ‘esca’ disease of grapevines. The possible role of such fungal metabolites in inducing symptoms on leaves and berries was studied in a vineyard of Vitis vinifera cv. Italia located in southern Italy. During early spring, pruning off two to four branches per vine allowed samples of xylem sap to be collected. Vine bleeding, assessed as ml day⁻¹ vine⁻¹, reached its maximum at bud burst and stopped within 28 days. The total amount of sap collected from healthy vines was about a quarter of that from esca-affected vines. During the same period, the leaf water potential of diseased vines increased progressively (i.e. showed less negative values), indicating a dysfunction in water and nutrient supply to the new growth. Both fungi were isolated from the xylem sap and from the woody tissue of branches and the trunk of diseased vines. Conidia isolated from the sap showed a high germination rate (>90%). Bioactive concentrations of the two pentaketides were detected in xylem sap, leaves and berries at various stages of seasonal growth. Exopolysaccharides, including pullulan, were found in the xylem sap. Absorption of culture filtrates of Pch and Tmi, as well as weak solutions of purified preparations of scytalone, isosclerone or pullulan, on detached leaves and berries caused symptoms similar to those shown by the esca-affected vines in the field.     

Co‐infection by Botryosphaeriaceae and Ilyonectria spp. fungi during propagation causes decline of young grafted grapevines

Decline of newly planted, grafted grapevines is a serious viticultural problem worldwide. In the Riverina (New South Wales, Australia), characteristic symptoms include low fruit yields, very short shoots and severely stunted roots with black, sunken, necrotic lesions. To determine the cause, roots and wood tissue from affected plants in 20 vineyards (Vitis vinifera cv. Chardonnay grafted to V. champini cv. Ramsey rootstock) were assayed for microbial pathogens. Ilyonectria spp. (I. macrodidyma or I. liriodendra, producers of phytotoxin brefeldin A, BFA, and cause of black foot disease of grapevines) and Botryosphaeriaceae spp. (predominantly Diplodia seriata) were isolated from rootstocks of 100 and 95% of the plants, respectively. Togninia minima and Phaeomoniella chlamydospora (cause of grapevine Petri disease) were isolated from 13 and 7% of affected plants, respectively. All Ramsey rootstock stems of grafted plants sampled from a supplier nursery were infected with Ilyonectria spp. and D. seriata. Diplodia seriata, but not Ilyonectria spp., was also isolated from 25% of canes sampled from the rootstock source block. Root inoculation of potted, disease‐free Chardonnay plants with Ilyonectria isolates from diseased vineyards caused typical disease symptoms, while co‐inoculation with Botryosphaeriaceae spp. increased disease severity. This is the first study to show that a major cause of young grapevine decline can be sequential infection by Botryosphaeriaceae from rootstock cuttings and Ilyonectria spp. from nursery soil. Although the Petri disease fungi were less common in young declining grafted grapevines in the Riverina, they are likely to contribute to the decline of surviving plants as they mature.     

Vertical dispersal of plant pathogens by splashing. Part I: the theoretical relationship between rainfall and upward rain splash

The theoretical relationship between rainfall intensity, raindrop size distribution and the upward transport of splash droplets is examined to establish a better understanding of the natural rainfall characteristics that can cause upward movement of plant pathogens in a crop. The theory suggests that splash transport is determined by the rain splash intensity index, which is defined as the intensity of the rainfall with raindrops greater than a threshold size. Ulbrich's (1983) empirical model of the size distribution of raindrops is used to calculate the relationship between rainfall intensity and rain splash intensity index. The calculations show that rainfall intensity is not a reliable indicator of the rain splash intensity index, particularly in convective showers. Therefore, a correlation between rainfall volume and upward disease progress is unlikely to provide a reliable basis for forecasting sudden disease outbreaks associated with short-duration convective showers during the summer. Finally, we consider the instruments that have the capability to measure the rain splash intensity index.