Individual-based approach to modeling hyphal growth of a biocontrol fungus in soil

ABSTRACT Fungi in soil perform beneficial roles that include biological control of soilborne plant pathogens. However, relatively little predictive information is available about the growth and activity of fungal hyphae in soil habitats. A stochastic computer simulation model ("Fungmod") was developed to predict hyphal growth of the biocontrol fungus Trichoderma harzianum ThzID1 in soil. The model simulates a fungal colony as a population of spatially referenced hyphal segments, and is individual-based, in that records of spatial location and branching hierarchy are maintained for individual hyphal nodes. In this way, the entire spatial structure of the fungal colony (hyphal network) can be explicitly reconstructed at any point in time. Also, the soil habitat is modeled as a population of spatially referenced 1-mm(3) soil cells, allowing for the simulation of a spatially heterogeneous environment. Initial hyphal growth parameters were derived from previously published results, and the model was tested against new data derived from image analysis of hyphal biomass accumulation in soil. The ability to predict fungal growth in natural habitats will help to improve the predictability of successful myco-parasitic events in biological control systems.     

Use of Green Fluorescent Protein and Image Analysis to Quantify Proliferation of Trichoderma harzianum in Nonsterile Soil

ABSTRACT One drawback of traditional methods for fungal biomass measurement is the inability to distinguish biomass of an introduced fungus from that of the indigenous microbial community in nonsterile soil. We quantified biomass of a specific fungal biological control agent in nonsterile soil using epifluorescence microscopy and image analysis of green fluorescent protein (GFP)-expressing Trichoderma harzianum (ThzID1-M3). Numbers of colony forming units on a semiselective medium were compared with biomass estimates from image analysis, after ThzID1-M3 was incubated in soil that either remained moist (-0.05 MPa) for 14 to 21 days or remained moist for approximately 5 days and then was allowed to dry to <-3.0 MPa. Recovery of significant numbers of ThzID1-M3 propagules lagged approximately 3 days behind initiation of hyphal growth. Reductions in both colony counts and biomass were observed over time when soil was allowed to dry. However, in soil that remained moist, colony counts increased over a 14- to 21-day period even though biomass declined after approximately 3 to 5 days. Our results confirm that use of GFP, along with epifluorescence microscopy, is a useful tool to distinguish active hyphal biomass, the form of the fungus that is functional for biological control, from inactive propagules such as conidia or chlamydospores that are enumerated by plate counts.     

多菌灵/戊唑醇复配对小麦赤霉病菌抗药性菌株的活性增效作用

为了解决小麦赤霉病菌抗药性以及明确杀菌剂复配增效作用,采用菌丝生长速率法、孢子萌发法、渗透压测定、甾醇含量测定等方法研究了多菌灵与戊唑醇复配对赤霉病菌抗药性菌株Nj-1-1的活性增效作用。研究表明:复配药剂虽不能完全抑制孢子萌发及菌丝生长,但可以减慢孢子萌发速率,同时破坏抗性菌株细胞膜的渗透性及内含物,从而初步解释多菌灵与戊唑醇复配组合的增效原因。     

A note on the mode of action of the systemic fungicide tridemorph

The effects of the systemic fungicide tridemorph on fungal and plant protoplasts have been investigated. No evidence of reaction at the plasma-membrane was revealed by microelectrophoresis. The fungicide did not affect oxygen uptake by fungal protoplasts but incorporation of labelled histidine was reduced. Fungi-toxicity tests showed that tridemorph had little effect on spore germination but inhibited mycelial growth. It is suggested that the fungicide may act by interfering with the synthesis of proteins essential for hyphal extension.     

Changes in soil microbial community response to precipitation events in a semi-arid steppe of the Xilin River Basin,China

In the context of climate change, precipitation is predicted to become more intense at the global scale. Such change may alter soil microbial communities and the microbially mediated carbon and nitrogen dynamics. In this study, we experimentally repackaged precipitation patterns during the growing season(from June to September) of 2012 in a semi-arid temperate steppe of the Xilin River Basin in Inner Mongolia of China, based on the 60-year growing season precipitation data. Specifically, a total amount of 240 mm simulated precipitation was assigned to experimental plots by taking the following treatments:(1) P6(6 extreme precipitation events, near the 1~(st) percentile);(2) P10(10 extreme precipitation events, near the 5~(th) percentile);(3) P16(16 moderate precipitation events, near the 50~(th) percentile); and(4) P24(24 events, 60-year average precipitation, near the 50~(th) percentile). At the end of the growing season, we analyzed soil microbial community structure and biomass, bacterial abundance, fungal abundance and bacterial composition, by using phospholipid fatty acid(PLFA), real-time quantitative polymerase chain reaction(RT-qPCR) and 16S rRNA gene clone library methods. The extreme precipitation events did not change soil microbial community structure(represented by the ratio of PLFA concentration in fungi to PLFA concentration in bacteria, and the ratio of PLFA concentration in gram-positive bacterial biomass to PLFA concentration in gram-negative bacterial biomass). However, the extreme precipitation events significantly increased soil microbial activity(represented by soil microbial biomass nitrogen and soil bacterial 16S rRNA gene copy numbers). Soil fungal community showed no significant response to precipitation events. According to the redundancy analysis, both soil microbial biomass nitrogen and soil ammonium nitrogen(NH_4-N) were found to be significant in shaping soil microbial community. Acidobacteria, Actinobacteria and Proteobacteria were the dominant phyla in soil bacterial composition, and responded differently to the extreme precipitation events. Based on the results, we concluded that the extreme precipitation events altered the overall soil microbial activity, but did not impact how the processes would occur, since soil microbial community structure remained unchanged.     

Effects of tebuconazole on morphology,structure, cell wall components and trichothecene production of Fusarium culmorum in vitro

The effects of tebuconazole, a systemic fungicide, on the morphology, structure, cell wall components and toxin production of Fusarium culmorum were investigated in vitro. Treatment was by application of four filter paper strips (0.75 cm × 5.0 cm) soaked in 20 µg ml ^?1 fungicide placed around a point inoculum in Petri dishes. Mycelial growth was strongly inhibited by fungicide treatment. Scanning electron microscopic observations showed that the fungicide caused irregular swelling and excessive branching of hyphae. The morphological changes induced by the fungicide at the ultrastructural level included considerable thickening of the hyphal cell walls, excessive septation, the formation of the incomplete septa, extensive vacuolisation, accumulation of lipid bodies and progressing necrosis or degeneration of the hyphal cytoplasm. Non‐membrane inclusion bodies were often detected in the hyphal cytoplasm. Furthermore, the formation of new hyphae (daughter hyphae) inside collapsed hyphal cells was common following treatment. The daughter hyphae also displayed severe alterations such as irregular thickening of the cell walls and necrosis of the cytoplasm. Using cytochemical techniques, the labelling densities of chitin and β‐1,3‐glucan in the cell walls of the fungicide‐treated hyphae were more pronounced than in those of the control hyphae. Moreover, immunogold labelling with antiserum against deoxynivalenol (DON) revealed that Fusarium toxin DON was localized in the cell walls, cytoplasm, mitochondria and vacuoles of the hyphae from the control and the fungicide treatment, but the labelling density in the fungicide‐treated hyphae decreased dramatically compared with the control hyphae, indicating that tebuconazole reduced Fusarium toxin production of the fungus. © 2001 Society of Chemical Industry     

农牧交错带不同植被群落对土壤微生物量碳氮磷的影响

为了解荒漠化土地植被恢复对土壤微生物量的影响,以地处毛乌素沙地南缘的榆林市沙生植物园植被恢复30年的乔木、灌木和草地3种植被群落下土壤为研究对象,分析了植被恢复对土壤微生物量碳、氮、磷含量及比值的影响及其与土壤理化性质的相关性。结果表明,农牧交错带荒漠化土地植被恢复可以明显提高表层土壤微生物碳、氮、磷的含量。土壤微生物量碳以灌木林地为最高,含量为288.35 mg·kg-1,显著高于草地和乔木,分别是乔木林地和草地的3.99和2.10倍;土壤微生物磷在三种植被群落间差异不明显;三种植被群落下土壤微生物碳氮比的高低为乔木林地草地灌木林地,土壤微生物碳磷比表现为草地略高于乔木林地和灌木林地。相关性分析结果显示微生物量碳、氮、磷与土壤理化性质相关性极为密切,其中与土壤养分各指标大多呈现极显著相关,与土壤容重多为极显著负相关。说明土壤微生物量可以作为评价土壤质量的生物学指标。     

Effects of the fungicide triphenyltin hydroxide on soil fauna mediated litter decomposition

The effects of an organotin pesticide, fentin hydroxide (triphenyltin (IV) hydroxide; TPTH) , on the soil fauna mediated decomposition of poplar leaf litter were examined. The responses of micro-ecosystems (MES) containing soil animals were compared to MES without fauna. The isopod Porcellio scaber Latr. was chosen as a representative saprotrophic soil fauna species. TPTH was added in four concentrations, ranging from 0.1 to 100 μg (g dry litter)^?1. MES respiration was used as a measure of decomposition rate. To measure the nitrogen mineralisation by microflora and isopods, ammonium and nitrate concentrations in the litter were determined. Analyses of the litter showed that TPTH was not degraded during the experiment. TPTH had a short-term effect on microbial respiration, which diminished after two days. Ammonium production by isopods within the system was the most sensitive parameter for the effects of TPTH . The No Observed Effect Concentration (NOEC) was 10 μg g^?1. It was concluded that, while TPTH is a fungicide, it does not seem to be very toxic to microbial respiration and ammonification as measured within the micro-ecosystem; isopod activities are more sensitive.     

Multiple resistance of Botrytis cinerea from kiwifruit to SDHIs,QoIs and fungicides of other chemical groups

BACKGROUND: Botrytis cinerea Pers.: Fr. is a high‐risk pathogen for fungicide resistance development that has caused resistance problems on many crops throughout the world. This study investigated the fungicide sensitivity profile of isolates from kiwifruits originating from three Greek locations with different fungicide use histories. Sensitivity was measured by in vitro fungitoxicity tests on artificial nutrient media. RESULTS: Seventy‐six single‐spore isolates were tested for sensitivity to the SDHI fungicide boscalid, the QoI pyraclostrobin, the anilinopyrimidine cyprodinil, the hydroxyanilide fenhexamid, the phenylpyrrole fludioxonil, the dicarboxamide iprodione and the benzimidazole carbendazim. All isolates from Thessaloniki showed resistance to both boscalid and pyraclostrobin, while in the other two locations the fungal population was sensitive to these two fungicides. Sensitive isolates showed EC₅₀ values to boscalid and pyraclostrobin ranging from 0.9 to 5.2 and from 0.04 to 0.14 mg L^?1 respectively, while the resistant isolates showed EC₅₀ values higher than 50 mg L^?1 for boscalid and from 16 to > 50 mg L^?1 for pyraclostrobin. All QoI‐resistant isolates carried the G143A mutation in cytb. Sensitivity determinations to the remaining fungicides revealed in total eight resistance phenotypes. No isolates were resistant to the fungicides fenhexamid and fludioxonil. CONCLUSION: This is the first report of B. cinerea field isolates with resistance to both boscalid and pyraclostrobin, and it strongly suggests that there may be a major problem in controlling this important pathogen on kiwifruit. Copyright © 2010 Society of Chemical Industry     

施氮和覆膜对旱作春玉米农田土壤微生物量和土壤酶活性的影响

为研究长期不同施氮水平和覆膜对黄土高原旱作春玉米高产体系土壤微生物活性的影响,设置田间试验包含施氮水平和覆膜2个因子,施氮量分别为0（N0）、100 kg·hm^-2（N100）、250 kg·hm^-2（N250）和400 kg·hm^-2（N400）,每个施氮水平下分别有覆膜（F）与不覆膜（B）处理,供试玉米品种为先玉335。2014年采集0~10 cm和10~20 cm土层土壤样品,测定土壤微生物量和酶活性,分析微生物量计量学特征并进行综合评价。结果表明,无论覆膜与否,土壤微生物量碳、氮和磷均随施氮量的增加而增加（除不覆膜时N400处理）,施氮量高于250 kg·hm^-2时土壤微生物量增加不显著。覆膜对土壤微生物量碳、氮无显著影响,而显著增加土壤微生物量磷;覆膜在一定程度上降低N0、N100和N400处理土壤微生物量碳氮比,施氮则显著增加微生物量碳氮比和微生物量氮磷比。0~10 cm土层脲酶活性随施氮量的增加而增加,但覆膜对脲酶活性无显著影响。覆膜和施氮均显著增加碱性磷酸酶活性,0~10 cm和10~20 cm土层覆膜N400处理碱性磷酸酶活性在相应土层最大,分别为1.49 mg·g^-1·d^-1和1.61 mg·g^-1·d^-1。主成分分析结果表明施氮量为250 kg·hm^-2时土壤微生物活性最强。研究表明无论覆膜与否,250 kg·hm^-2的施氮量是该地区适宜的施氮量。     

Metrafenone: studies on the mode of action of a novel cereal powdery mildew fungicide

Powdery mildew fungi are among the major pathogens causing diseases of cereals in the world. The mode of action of a novel systemic benzophenone fungicide, metrafenone, which is based on a precursor that is discussed in the preceding paper, has been analysed on the powdery mildew fungi of barley (Blumeria graminis Speer f. sp. hordei Marchal) and wheat (Blumeria graminis Speer f. sp. tritici Marchal). Preventive treatments reduced germination and blocked development beyond formation of appressoria, which penetrated less often. Moreover, metrafenone turned out to be an efficient curative fungicide, which rapidly affected fungal survival at low concentrations. The fungicide induced swelling, bursting and collapse of hyphal tips, resulting in the release of globules of cytoplasm. Bifurcation of hyphal tips, secondary appressoria and hyperbranching were also frequently observed. A histochemical analysis showed that metrafenone caused disruption of the apical actin cap and apical vesicle transport as well as weakening of the cell wall at hyphal tips. Finally, metrafenone strongly reduced sporulation. Reduced sporulation was associated with malformation of conidiophores that showed irregular septation, multinucleate cells and delocalisation of actin. Microtubules appeared to be only secondarily affected in metrafenone-treated B. graminis. The results suggest that the mode of action of metrafenone interferes with hyphal morphogenesis, polarised hyphal growth and the establishment and maintenance of cell polarity. Metrafenone likely disturbs a pathway regulating organisation of the actin cytoskeleton.     

Testing of an integrated regime for effective and sustainable control of invasive Crofton weed (Ageratina adenophora) comprising the use of natural inhibitor species,activated charcoal,and fungicide

Crofton weed is a major invasive species in China. It exhibits superior growth characteristics and can outcompete with native species via allolepathic effects and modulation of the soil fungal microbiome. The simple removal of invading plants will not ensure restoration of the habitat due to the persistence of allelochemicals and viable seeds in the surrounding soil. An orthogonal experimental design was employed to evaluate the effects of three control factors (A, powdered natural inhibitor species to retard growth; B, activated charcoal to absorb allelochemicals; and C, fungicide to reduce fungal modulation effects), applied at three levels, on the growth and competitive ability of Crofton weed against two native species, in a pot‐culture experiment. All treatments reduced all measured growth parameters (P < 0.05) except for a specific leaf area, when compared with control plants. Furthermore, the competitive capacity of Crofton weed was decreased in the treatments while that of the native species was improved. Application to soil of the powdered natural inhibitor species and of activated charcoal significantly inhibited plant growth and competitive ability of Crofton weed (P < 0.05). Application of fungicide was less effective, but significantly reduced the specific leaf area of Crofton weed plants (P < 0.05). The specific combination of factors producing the greatest decrease in plant growth and competitive ability (compared with the control) included the addition of Delavaya toxocarpa powder (37.5 g per kg soil), addition of activated charcoal to soil at a ratio of 1:3 (v/v) (62.5 g per kg soil), and application of fungicide (Thiophanate‐Methyl) (0.28 g per kg soil).     

Quantitative PCR monitoring of the effect of azoxystrobin treatments on Mycosphaerella graminicola epidemics in the field

Quantitative PCR and visual monitoring of Mycosphaerella graminicola epidemics were performed to investigate the effect of curative and preventative applications of azoxystrobin in wheat field crops. A non-systemic protectant and a systemic curative fungicide, chlorothalonil and epoxiconazole, respectively, were used as references. PCR diagnosis detected leaf infection by M graminicola 3 weeks before symptom appearance, thereby allowing a clear distinction between curative and preventative treatments. When applied 1 week after the beginning of infection, azoxystrobin curative activity was intermediate between chlorothalonil (low effect) and epoxiconazole. When applied preventatively, none of the fungicides completely prevented leaf infection. There was some indication that azoxystrobin preventative treatments may delay fungal DNA increase more than epoxiconazole at the beginning of leaf infection. Both curative and preventative treatments increased the time lapse between the earliest PCR detection and the measurement of a 10% necrotic leaf area. Azoxystrobin only slightly decreased the speed of necrotic area increase compared with epoxiconazole. Hence, azoxystrobin activity toward M graminicola mainly resides in lengthening the time lapse between the earliest PCR detection and the measurement of a 10% necrotic leaf area. Information generated in this way is useful for optimal positioning of azoxystrobin treatments on M graminicola.     

Effect of propiconazole on growth and sterol biosynthesis by Sclerotium rolfsii

Germination of sclerotia ofSclerotium rolfsii on agar nutrient medium was delayed or slightly inhibited by concentrations of propiconazole between 0.4 and 4.0 μg ml^?1, but was strongly inhibited by 8 μg ml^?1 and completely inhibited by 16 μg ml^?1. On the other hand, growth of hyphae from the germinated sclerotia was strongly inhibited by propiconazole at 1 μg ml^?1 or greater. Hyphal growth from agar discs on agar medium was about 8 times less sensitive than hyphal growth from the sclerotia or from hyphal inoculum in liquid media. Propiconazole at 0.25 and 1.0 μg ml^?1 strongly inhibited ergosterol biosynthesis, but this was not associated with large accumulations of C-14 methyl sterols. The ratio of eburicol to ergosterol in hyphae grown in the presence of 0.25 μg ml^?1 propiconazole for 16, 30 or 45 h was 0.11, 0.13 and 0.04, respectively, for the three intervals while for hyphae grown in the presence of 1 μg ml^?1, the ratios were 0.29, 0.36 and 0.30, respectively, for the same intervals. In view of a ratio of 23.5 for¹⁴C-acetate incorporation into the two sterols during the initial 6 h growth period in the presence of propiconazole, it is believed that the lack of large accumulation of C-14 methyl sterols is due to the feedback inhibition by eburicol or to cell lysis when the content of ergosterol becomes too low in the actively growing cells.     

不同改良材料对灌漠土微生物量磷及生物有效性的影响

通过培养和盆栽试验,向灌漠土土壤中加入等量磷和不同添加比例的硫磺S（0.05%、0.15%、0.45%）、生物菌肥B（0.25%、0.50%、1.00%）、有机肥OM（0.50%、1.00%、2.00%）和小麦秸秆WS（1.00%、2.00%、4.00%）,研究不同改良材料配施磷肥土壤微生物量磷的变化特征,及其与Olsen P、小麦吸磷量之间的关系。结果表明,添加不同改良材料处理的土壤微生物量磷含量均显著高于对照（不添加改良材料）,且随着添加比例的增大而增加。在第16天时,各处理土壤微生物量磷含量达到最大值,OM₂2.00、B₂1.00、WS₂4.00和S₂0.45处理分别较对照显著增加了34.66%、34.52%、28.19%和23.89%;经过30 d的培养,硫磺、生物菌肥、有机肥和小麦秸秆处理的土壤微生物量磷含量较对照分别增加了19.51%、43.08%、47.92%和41.68%。在一定范围内（Olsen P约90 mg·kg^-1）,土壤微生物量磷随土壤Olsen P提高而增加。在培养的第16天和第30天时,小麦植株吸磷量也与土壤微生物量磷存在极显著的相关关系。总体看来,有机肥或生物菌肥配合磷肥施用于灌漠土能促进土壤微生物量磷的增加,提高磷的生物有效性,对于灌漠土磷素高效利用具有重要意义。     

Behaviour of metamitron and hydroxy-chlorothalonil in low-humic sandy soils

The behaviour of the herbicide metamitron and of the main transformation product, hydroxy-chlorothalonil (HTI), of the fungicide chlorothalonil was studied to assess the risk of leaching from low-humic sandy soil. The adsorption of metamitron corresponded to a K_om value of about 60 dm³ kg⁻¹ (moderate adsorption). The half-life of metamitron in soil at 15 °C was only three days, presumably due to adaptation of the micro-organisms. In the autumn, the residue of metamitron in the soil profiles corresponded to less than 1% of the cumulative dosage. The half-life of chlorothalonil at 15 °C was about 12 days and about 45% of it was transformed to HTI. The adsorption of HTI to the soils corresponded to a K_om value of 260 dm³ kg⁻¹. The incubation study (15 °C) showed the transformation of HTI in the soils to be very slow. The amounts of HTI remaining in the soil profiles in the autumn corresponded to 4 and 16% of the cumulative dosage of chlorothalonil. In winter, the HTI residue decreased by 40% relative to the autumn level. Occasionally, HTI could be detected in the upper ground-water level (at a depth of about 1 m), at an average concentration of 0.1 to 0.2 µg dm⁻³. © 1999 Society of Chemical Industry     

Mechanism of action and fate of the fungicide chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) in biological systems: I. Reactions with cells and subcellular components of Saccharomyces pastorianus

The mechanism and sequence of reaction of chlorothalonil in cells of Saccharomyces pastorianus was investigated by the use of either ¹⁴C-labeled fungicide or Na₂³⁵SO₄-labeled cells. The initial uptake of fungicide resulted in rapid formation of substituted chlorothalonil-reduced glutathione (GSH) derivatives. Chlorothalonil reacted with proteins during derivative formation but decreased cell viability did not occur until all the GSH was reacted and inhibition of specific NAD thiol-dependent glycolytic and respiratory enzymes occurred. It is postulated that enzyme activity and cell viability are controlled either directly or indirectly by the concentration of GSH. The loss of GSH through derivative formation with chlorothalonil and the lack of regeneration of the reduced thiol could be an important feature in the sequence of toxicity of the fungicide. The general mechanism of action of chlorothalonil resembles the trichloromethyl sulfenyl fungicides in that treated cells accumulate large concentrations of fungicide; reactions involve both low and high molecular-weight thiols, with the formation of glutathione-fungicide derivatives; and toxicity resides ultimately with the inhibition of thiol-dependent enzymes.     

Characteristics of alginate pellets formulated with Trichoderma and Gliocladium and their effect on the proliferation of the fungi in soil

Pelletized formulations of wheat bran or kaolin clay in an alginate gel containing conidia, chlamydospores, or fermentor biomass (FB) of several isolates of the biocontrol fungi Trichoderma spp. and Gliocladium virens were prepared. The ability of fungal propagules within the pellets to proliferate in soil was determined. Higher population densities were obtained when alginate pellets added to soil contained chlamydospores rather than condia, and bran rather than kaolin as the bulking agent. The active ingredient in pellets prepared from FB was approximately 5% biomass by weight and contained many chlamydospores. Colony-forming units (cfu) ranged from 10⁶'to 10¹⁰/g of soil after soil amendment with FB pellets of 12 Trichoderma and G. virens isolates. Population densities were high during the first 3 weeks of incubation and declined only gradually during 9 weeks. Propagules in FB pellets were more viable at 5° than at 25°C. Viability at 25°C remained high (> 70%) after 1 week, but declined to less than 10% after 24 weeks. Despite reduction in propagule viability in stored pellets, numbers of cfu formed after adding these pellets to soil were comparable with those formed from freshly prepared pellets.     

Relationship between the Spray Droplet Density of Two Protectant Fungicides and the Germination of Mycosphaerella fijiensis Ascospores on Banana Leaf Surfaces

The effect of fungicide spray droplet density (droplet cm^-2), droplet size, and proximity of the spray droplet deposit to fungal spores was investigated with Mycosphaerella fijiensis ascospores on the banana (Musa AAA) leaf surface for two contact fungicides: chlorothalonil and mancozeb. When droplet size was maintained at a volume median diameter (VMD) of 250 μm while total spray volume per hectare changed, M. fijiensis ascospore germination on the leaf surface fell below 1% for both fungicides at a droplet deposit density of 30 droplet cm^-2. At a droplet deposit density of 50 droplet cm^-2, no ascospores germinated in either fungicide treatment. When both droplet size and droplet cm^-2 varied while spray volume was fixed at 20 litre ha^-1, ascospore germination reached 0% at 10 droplet cm^-2 (VMD=602 μm) for both fungicides. At lower droplet densities (2–5 droplet cm^-2 VMD=989 μm and 804 μm respectively), ascospore germination on the mancozeb-treated leaves was significantly lower than on the chlorothalonil-treated leaves. The zone of inhibition surrounding a fungicide droplet deposit (VMD=250 μm) on the leaf surface was estimated to extend 1·02 mm beyond the visible edge of the spray droplet deposit for chlorothalonil and 1·29 mm for mancozeb. The efficacy of fungicide spray droplet deposit densities which are lower than currently recommended for low-volume, aerial applications of protectant fungicides was confirmed in an analysis of leaf samples recovered after commercial applications in a banana plantation. Calibrating agricultural spray aircraft to deliver fungicide spray droplets with a mean droplet deposit density of 30 droplet cm^-2 and a VMD between 300 and 400 μm will probably reduce spray drift, increase deposition efficiency on crop foliage, and enhance disease control compared to aircraft calibrated to spray finer droplets. © 1997 SCI.     

Effects of repeated glyphosate applications on soil microbial community composition and the mineralization of glyphosate

Background: Repeated applications may have a greater impact on the soil microbial community than a single application of glyphosate. Experiments were conducted to study the effect of one, two, three, four or five applications of glyphosate on soil microbial community composition and glyphosate mineralization and distribution of ¹⁴C residues in soil. RESULTS: Fatty acid methyl esters (FAMEs) common to gram‐negative bacteria were present in higher concentrations following five applications relative to one, two, three or four applications both 7 and 14 days after application (DAA). Additionally, sequencing of 16S rRNA bacterial genes indicated that the abundance of the gram‐negative Burkholderia spp. was increased following the application of glyphosate. The cumulative percentage ¹⁴C mineralized 14 DAA was reduced when glyphosate was applied 4 or 5 times relative to the amount of ¹⁴C mineralized following one, two or three applications. Incorporation of ¹⁴C residues into soil microbial biomass was greater following five glyphosate applications than following the first application 3 and 7 DAA. CONCLUSION: These studies suggest that the changes in the dissipation or distribution of glyphosate following repeated applications of glyphosate may be related to shifts in the soil microbial community composition. Copyright © 2009 Society of Chemical Industry