Control Of Canker Research Articles

Potential use of cuminic acid as a botanical fungicide against Valsa mali.

Valsa canker caused by Valsa mali is commonly present in eastern Asia and cause large economic losses. Because of limited agricultural measures and chemical residues of commonly used fungicides there is an urgent need of alternative plant protecting agents. On this background the activity of cuminic acid, a plant extract from the seed of Cuminum cyminum L, was assessed. The median effective concentration (EC50) values for inhibition of mycelial growth of seven V.mali strains ranged from 3.046 to 8.342μg/mL, with an average EC50 value of 4.956±0.281μg/mL. The antifungal activity was the direct activity of cuminic acid instead of the influence on the pH of media by cuminic acid. After treated with cuminic acid, mycelia dissolved with decreased branches and swelling; cell membrane permeability increased while pectinases activity decreased significantly. Moreover, peroxidase (POD) activity of the apple leaves increased after treated with cuminic acid. Importantly, on detached branches of apple tree, cuminic acid exhibited both protective and curative activity. These results indicated that cuminic acid not only showed the antifungal activity, but also could improve the defense capacity of the plants. Taken together, cuminic acid showed the potential as a natural alternative to commercial fungicides or a lead compound to develop new fungicides for the control of Valsa canker.

Management of Chinese hickory (Carya cathayensis) trunk canker through effective fungicide application programs and baseline sensitivity of Botryosphaeria dothidea to trifloxystrobin

Trunk canker of Chinese hickory (Carya cathayensis), caused by Botryosphaeria dothidea, is the most important disease threatening production. Although fungicides are applied to control the disease, efficacy is very poor. In this study, fungicides were studied and selected for effective control of trunk canker through assessments of inhibitory activity and application programs. Seventeen fungicides from eight different FRAC groups were tested for their in vitro activity against B. dothidea. Difenoconazole, tebuconazole, and prochloraz (FRAC 3) were the most effective in inhibiting mycelial growth. Trifloxystrobin (FRAC 11) had the most significant inhibitory activity against spore germination with an EC50 of 1.78 ± 0.61 mg/ L. Seven different application programs with three sprays of trifloxystrobin and/or difenoconazole for each program were evaluated at two forest sites over 3 years. Results indicated that the date of the first spray is crucial. If the first spray was applied on March 10, significantly better efficacy was achieved compared to an application on March 20. In 2016, a real-time PCR technique was adopted to help quantify the pathogen and thereby assess canker control. The results suggested a good relationship between gDNA content of B. dothidea in trunk tissues and the development of the canker lesions at both sites. Moreover, a total of 107 single-conidium isolates of B. dothidea were further tested for their sensitivities to trifloxystrobin in conidial germination experiments. In the presence of 100 mg/L SHAM, the EC50 values ranged from 0.29 mg/L to 8.38 mg/L, with an average of 3.16 ± 0.85 mg/L. The range of variation was 28.9-fold. These sensitivity data can be used as a baseline for monitoring putative sensitivity shifts in B. dothidea to trifloxystrobin, a Qo-inhibiting (QoI) fungicide, members of which are commonly considered to be at a high risk for resistance selection.

Potential of Nano-Formulated Zinc Oxide for Control of Citrus Canker on Grapefruit Trees.

Antimicrobial activity of experimental formulations of two structurally different nano-zinc oxide materials, plate-like Zinkicide SG4 and particulate Zinkicide SG6, was evaluated against Xanthomonas citri subsp. citri, the cause of citrus canker. In vitro assay demonstrated Zinkicide SG4 had a twofold lower minimum inhibitory concentration (MIC) against Escherichia coli and X. alfalfae subsp. citrumelonis (62.5 to 250 µg/ml) compared with copper sulfate (250 µg/ml), copper hydroxide (250 to 500 µg/ml), or cuprous oxide/zinc oxide (125 to 250 µg/ml). Zinkicide SG6 had a sevenfold to eightfold lower MIC against Escherichia coli and X. alfalfae subsp. citrumelonis (31 to 250 μg/ml). Leaves of sweet orange (Citrus sinensis) and fruit of 'Ruby Red' grapefruit (C. paradisi) were evaluated for citrus canker disease control. A greenhouse assay with foliage demonstrated that spray treatment with Zinkicide reduced citrus canker lesion development after injection-infiltration of X. citri subsp. citri into the leaf intercellular space. In field trials conducted in Southeast Florida in 2014 and 2015, Zinkicide SG4 and SG6 reduction of grapefruit canker incidence exceeded that of cuprous oxide and cuprous oxide/zinc oxide bactericides. Zinkicide formulations were also effective against the fungal diseases, citrus scab (Elsinoe fawcetti) and melanose (Diaporthe citri), on grapefruit. No sign of phytotoxicity to the fruit rind was observed during either season. Antimicrobial activity of Zinkicide for protection of leaves and fruit against X. citri subsp. citri was comparable or exceeded that for commercial copper and zinc oxide formulations which may be attributed to translaminar movement of Zinkicide.

Evaluation of soil applied systemic acquired resistance inducers integrated with copper bactericide sprays for control of citrus canker on bearing grapefruit trees

Soil application of systemic neonicotinoid insecticides and the commercial systemic acquired resistance (SAR) inducer, acibenzolar-S-methyl (ASM), provides season-long control of foliar infection by Xanthomonas citri subsp. citri, the causal agent of citrus canker. Reduction in leaf disease incidence with ASM is comparable to protection with 21-day interval foliar sprays of copper hydroxide (CH). Soil applications of ASM alone, rotated with the neonicotinoids imidacloprid (IMID), thiamethoxam (THIA), and clothianidin (CLOTH), or combined with foliar sprays of CH were compared for canker disease control on fruit of 5- to 7-year-old bearing ‘Ruby Red’ grapefruit trees in Southeast Florida. All treatments significantly reduced the incidence of canker lesions on fruit compared to the untreated check. Soil drenches of ASM and season-long rotations with IMID, THIA, and CLOTH were as effective for suppressing fruit canker as season-long foliar sprays with CH. SAR inducers combined with CH sprays provided optimum control of fruit canker when initiated before the onset of the susceptible foliar flush in the spring. Additional control of canker with soil-applied SAR inducers may enable reduction in the frequency of copper sprays and reduce disease loss from copper resistant Xcc strains where they are prevalent.

Bacillus subtilis QST 713, copper hydroxide, and their tank mixes for control of bacterial citrus canker in Saudi Arabia

Citrus Bacterial Canker (CBC) is a serious disease that affects production of almost all commercial citrus cultivars in subtropical citrus growing regions worldwide. In this study, the effectiveness of monthly foliar sprays of wettable powder formulation Serenade MAX of Bacillus subtilis QST 713, alone or as tank mixes with copper hydroxide on CBC disease development was evaluated under greenhouse and uncovered nursery conditions. The QST 713 as a tank mix with copper hydroxide reduced significantly the disease severity and incidence, followed by the copper hydroxide treatment, compared to the control. The disease incidence on leaves of inoculated trees treated with a combination of copper with QST 713 was never higher than 19%, whereas, the disease incidence reached 43% for non-sprayed trees. It was possible to reduce the number of copper sprays up to 6 sprays per season when it was mixed with the bio-fungicide QST 713 to effectively control CBC compared with 8 sprays of copper hydroxide alone per season. Based on our results, the application of QST 713 not only may have potential for CBC management in conjunction with copper hydroxide or other disease control but also may reduce the frequency or rate of copper sprays in citrus groves.

Optimal Trichoderma strains for control of stem canker of brassicas: molecular basis of biocontrol properties and azole resistance

Genus Trichoderma contains the most powerful agents used in biocontrol. Our study demonstrated that T. harzianum, T. hamatum and T. longibrachiatum can effectively control phytopathogenic fungi Leptosphaeria maculans and L. biglobosa. The effects of Trichoderma on pathogens’ growth (in dual cultures on agar media) and on disease severity (on seedlings in controlled conditions) were also confirmed by field experiments. Additionally, spraying with conidiospores in the autumn was helpful in reducing the incidence and severity of phoma leaf spots. It has also accelerated the degradation of plant stubble and the decomposition of pathogens’ fruiting bodies. Furthermore, all Trichoderma isolates showed higher cellulolytic activity and enhanced resistance to flusilazole treatments as compared to Leptosphaeria spp., which coincided with upregulation of 14α-sterol demethylases and an AbcG5 transporter. The effects we observed justify the use of Trichoderma to enhance the resistance of oilseed rape against pathogens, which in turn may lead to a decrease in the use of pesticides.

Xanthomonas citri subsp. citri surface proteome by 2D-DIGE: Ferric enterobactin receptor and other outer membrane proteins potentially involved in citric host interaction

Xanthomonas citri subsp. citri (XAC) is the causative agent of citrus canker, a disease of great economic impact around the world. Understanding the role of proteins on XAC cellular surface can provide new insights on pathogen-plant interaction. Surface proteome was performed in XAC grown in vivo (infectious) and in vitro (non-infectious) conditions, by labeling intact cells followed by cellular lysis and direct 2D-DIGE analysis. Seventy-nine differential spots were analyzed by mass spectrometry. Highest relative abundance for in vivo condition was observed for spots containing DnaK protein, 60kDa chaperonin, conserved hypothetical proteins, malate dehydrogenase, phosphomannose isomerase, and ferric enterobactin receptors. Elongation factor Tu, OmpA-related proteins, Oar proteins and some Ton-B dependent receptors were found in spots decreased in vivo. Some proteins identified on XAC's surface in infectious condition and predicted to be cytoplasmic, such as DnaK and 60KDa chaperonin, have also been previously found at cellular surface in other microorganisms. This is the first study on XAC surface proteome and results point to mediation of molecular chaperones in XAC-citrus interaction. The approach utilized here can be applied to other pathogen-host interaction systems and help to achieve new insights in bacterial pathogenicity toward promising targets of biotechnological interest. Biological significanceThis research provides new insights for current knowledge of the Xanthomonas sp. pathogenicity. For the first time the 2D-DIGE approach was applied on intact cells to find surface proteins involved in the pathogen-plant interaction. Results point to the involvement of new surface/outer membrane proteins in the interaction between XAC and its citrus host and can provide potential targets of biotechnological interest for citrus canker control.

Bioactive Organocopper Compound from Pseudomonas aeruginosa Inhibits the Growth of Xanthomonas citri subsp. citri.

Citrus canker is a very destructive disease of citrus species. The challenge is to find new compounds that show strong antibiotic activity and low toxicity to plants and the environment. The objectives of the present study were (1) to extract, purify and evaluate the secondary metabolites with antibiotic activity produced by Pseudomonas aeruginosa LV strain in vitro against Xanthomonas citri subsp. citri (strain 306), (2) to determine the potential of semi-purified secondary metabolites in foliar application to control citrus canker under greenhouse conditions, and (3) to identify antibiotic activity in orange leaf mesophyll infected with strain 306, by electron microscopy. Two pure bioactive compounds were isolated, an organocopper antibiotic compound (OAC) and phenazine-1-carboxamide. Phenazine-1-carboxamide did not show any antibiotic activity under the experimental conditions used in this study. The OAC showed a high level of antibiotic activity with a minimum inhibitory concentration of 0.12 μg mL-1. In greenhouse tests for control of citrus canker in orange trees, the semi-purified fraction F3d reduced lesion formation by about 97%. The concentration used was 500 times lower than that for the recommended commercial copper-based product. Electron microscopy showed that F3d altered the exopolysaccharide matrix and caused cell lysis of the pathogen inside the citrus canker lesions. These results suggest that secondary metabolites produced by inducing P. aeruginosa LV strain have a high potential to be used as a bioproduct to control citrus canker.

The Evaluation of the Activity of Some Algae and Their Extracts on the Control of Stem Canker of Potato Caused by Rhizoctonia solani

This study is conducted at laboratories of College of Agriculture- university of Kufa in order to evaluate three algae Microcystis sp., spirulina eplatensis and sarconema sp. and their organic extracts against Rhizoctonia solani pathogen . The antagonistic ability of Microcystis is effective against R.sloni because it gives colony diameter 7mm , with inhibitory percentage 65% , as compared with control which gives 20mm of colony diameter .The results revealed that methanol extract was more effective in reducing the viable cells of R.solani which give 28.66 x 104 CFU/ml as compared to 32.40 x 104 CFU/ml at the control .Viable cells of R.solani are reduced with the application of Microcystis which is 26.46x104 CFU/ml as compare with spirulina platensis and sarconema which give 29.18 and 28.14x 104 CFU/ml respectively . The ethanolic extract of Microcystis sp. has the superiority of reducing colony diameter of R.solani , when gives inhibitory zone 26mm as compared with acetone as an extract of the same alga which gives inhibitory zone 20mm

Tree-row-volume-based sprays of copper bactericide for control of citrus canker

Commonly, pre-determined copper spray volumes are indiscriminately applied to citrus orchards of different ages and sizes for control of citrus canker (Xanthomonas citri subsp. citri) leading to a waste of resources, such as water, energy, and chemicals. This study evaluated the effectiveness of copper applied following the tree-row-volume (TRV) methodology for control of citrus canker on sweet orange trees. Treatment design was based on the theoretical runoff volumes previously determined for the exterior and interior of a citrus tree. The volumes 150 (standard), 100 (internal runoff point), 70 (intermediate) and 40 mL (external runoff point) of spray mixture/m3 of tree canopy were tested at the standard copper rate of 0.525 g metallic copper/L. Additionally, 70 and 40 mL/m3 were also tested with copper rate correction by leveling up the theoretical deposition of copper bactericide to that obtained with 100 mL/m3.Untreated control trees (UTC) were not sprayed with copper. Reduction of the spray volume did not affect disease control. While UTC trees presented a peak incidence of citrus canker on leaves of 30% in both years, copper-treated trees showed significantly lower peak incidences of 5–10%. Likewise, the average number of dropped fruits with citrus canker for the UTC was 2.0- to 1.5-fold higher than for copper treatments. At harvest, 30% of fruits from the UTC trees showed citrus canker symptoms. Conversely, only 3.3–9.8% of the fruits from the copper treatments were symptomatic. Moreover, using 40 mL/m3 without adjusting the amount of metallic copper diminished disease control efficiency on leaves. Reduction of spray costs and water needs amounted to 40 and 73%, respectively. In addition to keeping effectiveness of disease control and being more environmentally friendly, the adaptation of the spray volumes and copper rates to the TRV may contribute to reducing production costs.

Biological Control of Stem Canker and Black Scurf on Potato by Date Palm Compost and its Associated Fungi

AbstractThe suppressive effects of two different types of date palm composts and some of their indigenous microorganisms were evaluatedin vitroand on potato plants inoculated withRhizoctonia solani. Fungi isolated from composts screened againstR. solaniby dual cultural assays onPDAshowed a significant inhibition of pathogen mycelium growth as compared with untreated control. The type of hyphal interactions betweenR. solaniand each tested antagonist was observed by light microscopy. Microscopic observations carried out at the confrontation zone of both agents showed different mechanisms of actions: mycelia lyses, mycoparasitism and/or formation of mycelia cords via anatomosis between mycelia filaments. Unsterilized and sterilized compost extracts were tested for efficacy againstR. solaniusing agar‐well diffusion method or by pouring the extracts onPDA. Two sterilization methods were used: a filtration through a microfilter of 0.22 microns or autoclaving. Results showed that compost extract lost its activity after heating or filtration, confirming that chemical factors in compost had no direct inhibiting effect on the pathogen. The suppressiveness of composts was mainly due to their biotic component. Series of greenhouse trials showed that black scurf and stem canker incidence and severity were significantly reduced in peat–sand amended with compost compared with the untreated control. However, the potential suppressive effect of cattle manure and date palm compost (CMC) was higher than sheep manure and date palm compost (SMC). On potato seed tubers pre‐inoculated with the selected fungal isolates from compost, there was variability in the reduction of disease severity among treatments. Plant growth was unaffected by the application of fungal antagonists or byCMCamendment; however, an increase in the total yield was observed by theSMCpotting mix compared with untreated control.

Meta-modelling of the impacts of regional cropping system scenarios for phoma stem canker control

In agricultural landscapes, pest and disease control mainly rely on cropping system characteristics and location. We have combined a participatory approach and a spatially-explicit model, to design and assess cropping system scenarios for future contextual changes in the small region of Picardie, France. Phoma stem canker of winter oilseed rape (WOSR), a widespread disease responsible for major economic losses, was used as a case study to investigate the effects of modifying cropping systems, at a regional scale, on disease controlling and on the sustainability of a newly introduced specific resistance gene (RlmX). Meta-models were fitted to assess the effects of cropping practices and weather conditions included in scenarios on three complementary model outputs: size of the pathogen population, yield loss, and fraction of the virulent population on RlmX-cultivars. We ran three replicates of each cropping practice scenario, varying the location of WOSR and associated cropping characteristics within the region. Outputs differed slightly between replicates, but there were no significant differences between replicates (alpha=0.001) for each output. The size of the pathogen population was well explained by winter oilseed rape acreages, cultivar landscape composition and tillage, and the yield loss was explained by weather conditions and cultivars. The fraction of the virulent population on RlmX-cultivars was explained primarily by cultivar landscape composition. These differences in explanatory variables for the different outputs highlighted their complementarity. Cropping practices and weather impacts on the three variables remained consistent among the explored possible future contexts. Highlighting the most efficient cropping practices to be applied in the event of different future changes could help local decision-makers to design cropping practices in the face of contextual change.

Activity of Secondary Bacterial Metabolites in the Control of Citrus Canker

This study investigated the protective effects of secondary bacterial metabolites, produced by Pseudomonas sp. (bacterium strain LN), on citrus canker disease caused by Xanthomonas axonopodis pv. citri (Xac 306). The LN bacteria strain was cultured in liquid medium and the supernatant free-cells was treated with methanol (AMF) and ethyl acetate (AEF), respectively, and then the extract was concentrated, filtrated, lyophilized and fractionated by vacuum liquid chromatography (VLC). After VLC, eight fractions were obtained. All fractions’ activity against Xac 306 by agar well diffusion assay and minimum inhibitory concentration but in different concentrationswere tested. Cytotoxicity effects were observed in all fractions in 50 μg·mL-1 concentration. The comet assay demonstrated that the fractions EAF, VLC2 and VLC3 presented no genotoxic effects at tested concentrations. In plants only VLC3 showed significant results (p

Identification of Pseudomonas syringae pv. actinidiae strains causing bacterial canker of kiwifruit in the Anhui Province of China, and determination of their streptomycin sensitivities.

Bacterial canker, caused by Pseudomonas syringae pv. actinidiae, is one of the most severe diseases of kiwifruit. It has become an international pandemic and threatens the sustainable development of kiwifruit production in all main kiwi-growing regions worldwide. Streptomycin has been the major bactericide for the control of kiwifruit canker, especially in Anhui Province, one of the main kiwifruit production regions in China. However, until now, no studies on the baseline sensitivity to streptomycin of field isolates of P. syringae pv. actinidiae from China have been available. During 2012-2013, a total of 102 single-colony P. syringae pv. actinidiae strains were isolated: 36, 12, 13, 26, and 15 strains from Yuexi, Jinzhai, Huoshan, Qianshan, and Taihu counties, respectively. All strains were confirmed by production of a 280-bp fragment using the specific primers PsaF1/R2 upon polymerase chain reaction amplification, followed by an assay for confirmation of pathogenicity to fulfill Koch's postulates. In this study, the streptomycin sensitivity of the 102 isolated strains was determined. The half-maximal effective concentration values for inhibition of growth by streptomycin were 0.03-0.42 μg/mL (average 0.12 ± 0.06 μg/mL). The baseline sensitivity curve was unimodal, representing range-of-variation factors of 14.0. No resistant subpopulation was identified among the strains used in the study. Thus, these sensitivity data could be used as a baseline for monitoring the shift in sensitivity of P. syringae pv. actinidiae populations to streptomycin in Anhui Province. Continuous resistance monitoring should be carried out, as streptomycin is an at-risk bactericide agent.

English

Medicinal and aromatic plants (MAP) belonging to 16 species, currently used in southern Moroccan traditional medicine, were evaluated here, firstly, for the action of their aqueous extracts against the bacterial canker agent of tomato in vitro. Then the phenolic contents, flavonoids contents and antioxidant capacities of these MAP extracts were estimated. Results obtained show that tested species exhibited biological activity toward the pathogen studied here; the inhibition zone diameter was between 0.5 and 4.88 cm. Furthermore, tested species exhibited a board range of phenolic contents varying from 55.58 ± 5.07 to 3.98 ± 0.16 mg of Cafeic acid equivalents (CAE) per gram of dry weight (DW). The flavonoids contents varied from 19.82 ± 0.65 to 1.74 ± 0.34 mg of Rutine equivalents (RE) per g of DW. Significant and positive linear correlations were found between total phenolic contents (R = 0.87 and R2 = 0.76), flavonoids contents (R = 0.96 and R2 = 0.93) and the biologic activity (IZ diameters) of the aqueous extracts. The antioxidant capacity expressed as Trolox equivalents antioxidant capacity (TEAC) varied from 550.67 to 1.18 mM per 100 g dry weight. Significant and positive linear correlation was found also between antioxidant capacities and both phenolic and flavonoids contents. These results proved that the richness of MAP with phenols and flavonoids was involved in there antibacterial activity and there antioxidant capacity. This finding is useful and can contribute to the development of potent and natural bio pesticides in the future for the control of bacterial canker of tomato as well as other phytopathogens by exploiting MAP compounds accepted by consummators and environmentalists. Key words: Bacterial canker, tomato, medicinal plants, biological control, flavonoids, Trolox equivalents antioxidant capacity (TEAC), 2,2-diphenyl-1-picrylhydrazyl (DPPH).

Análise econômica da prevenção e controle do cancro cítrico no estado de São Paulo

No presente trabalho estimou-se a relação benefício-custo de estratégias diferentes de controle do cancro cítrico (a prevenção e erradicação ou manejo) no estado de São Paulo, onde a citricultura é uma das principais culturas agrícolas em produção e emprego. O índice de talhões contaminados com cancro cítrico aumentou 893% entre 2009 e 2012, logo após mudanças na legislação paulista de controle da doença, o que justifica a importância de analisar seus impactos econômicos, dado que o manejo da doença tem grande relevância econômica. Adota-se a Análise Benefício-Custo como instrumento para, ao identificar os custos e benefícios mais expressivos para o produtor rural, comparar a variação na produção e nos custos de produção. Para tanto, são simulados cenários de prevenção, controle ou manejo com expansão da doença, em um horizonte de 20 anos. Os resultados apontam vantagens econômicas em manter o cancro cítrico sob controle no estado de São Paulo, ou seja, sob níveis mais baixos de incidência, demonstrando que o manejo com expansão da doença no médio e longo prazos apresenta relação benefício-custo significativamente inferior à prevenção e controle da doença com erradicação rigorosa dos focos da doença.

Biology and control of the apple canker fungus Neonectria ditissima (syn. N. galligena) from a Northwestern European perspective

A review of apple canker caused by Neonectria ditissima is presented for Northwestern Europe with a focus on the Lower Elbe region (Northern Germany). Whereas conidia released by rainsplash are produced mainly from spring to autumn, the liberation of wind-borne ascospores peaks in autumn and/or early spring. Infection occurs via natural as well as pruning-induced wounds, some of which are present throughout the year. Autumnal leaf scars are the most frequent entry point for N. ditissima. Wounds on tree trunks, especially bark cracks in the crotch regions, are potentially even more serious because cankers on trunks and leader shoots commonly cause the total loss of a tree. Surface moisture is a prerequisite for leaf scar infections but possibly not for an entry through other wounds. Irrespective of the entry route, successful infection of a wound requires a mass inoculum of at least 50–100 conidia or ascospores. Infections of trees originating in nurseries may enter a state of latency from which they can break out up to 3 years after the trees have been explanted into the production orchard. Streaks of brown wood discolourations can be caused both by systemic colonisation of the xylem by N. ditissima and by winter frost damage. Apple varieties may show pronounced differences in their sensitivity to canker. For highly susceptible varieties, this disease can be a major production-limiting factor. Flower infections by N. ditissima commonly lead to a pre-harvest rot at the blossom end of the fruit, whereas infections of the growing fruit before harvest lead to a storage rot. Rigorous pruning is an essential canker control measure. Chemical control during the growing season is achieved by apple scab fungicides such as dithianone, captan or dodine. At leaf fall and in winter, copper fungicides are indispensible for controlling canker on highly susceptible varieties in Northern Germany.

Foliar Application of Biofilm Formation–Inhibiting Compounds Enhances Control of Citrus Canker Caused by Xanthomonas citri subsp. citri

Citrus canker caused by the bacterium Xanthomonas citri subsp. citri is an economically important disease of citrus worldwide. Biofilm formation plays an important role in early infection of X. citri subsp. citri on host leaves. In this study, we assessed the hypothesis that small molecules inhibiting biofilm formation reduce X. citri subsp. citri infection and enhance the control of citrus canker disease. D-leucine and 3-indolylacetonitrile (IAN) were found to prevent biofilm formation by X. citri subsp. citri on different abiotic surfaces and host leaves at a concentration lower than the minimum inhibitory concentration (MIC). Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis indicated that IAN repressed expression of chemotaxis/motility-related genes in X. citri subsp. citri. In laboratory experiments, planktonic and biofilm cells of X. citri subsp. citri treated with D-leucine and IAN, either alone or in combination, were more susceptible to copper (CuSO4) than those untreated. In greenhouse assays, D-leucine and IAN applied alone or combined with copper reduced both the number of canker lesions and bacterial populations of X. citri subsp. citri on citrus host leaves. This study provides the basis for the use of foliar-applied biofilm inhibitors for the control of citrus canker alone or combined with copper-based bactericides.

Sensitivity of <i>Neonectria ditissima</i> to carbendazim fungicide in New Zealand

Carbendazim can be used by New Zealand pipfruit growers for control of European canker caused by Neonectria ditissima A total of 162 N ditissima isolates were tested for carbendazim sensitivity using a mycelial growth assay on amended malt extract agar plates at concentrations from 02 mg/litre Generally isolates ceased growth at 2 mg/ litre carbendazim with 65 isolates ceasing growth at 1 mg/litre The EC50 values calculated for 19 isolates ranged from 051 to 138 mg/litre The data suggested that isolates ranged from sensitive (EC50100 mg/litre The isolates tested were mostly sensitive to carbendazim but some showed a shift towards intermediate resistance Mycelial growth tests at 2 mg/litre may be a useful tool to screen single spore isolates quickly for potential carbendazim resistance

カンキツかいよう病に対する非病原性<i>Xanthomonas</i>属細菌の防除効果

カンキツかいよう病に対する非病原性<i>Xanthomonas</i>属細菌の防除効果