Control Of Bacterial Spot Research Articles

파인 오일과 수산화동 혼합물에 의한 고추 세균점무늬병과 탄저병의 방제 효과

본 연구는 파인 오일과 수산화동의 혼용에 의한 고추의 세균성 점무늬병과 탄저병에 대한 방제 효과를 구명하고자 수행하였다. 세균성 점무늬병에 대한 방제 효과는 파인 오일만 단독 처리한 경우 발병엽률 59.6%와 방제 효과 28.9%로 나타났지만 파인 오일과 수산화동을 4:1로 혼용 처리하였을 때 발병엽률 20.0%와 방제효과 76.1%로 가장 효과적이었다. 탄저병에 대한 방제 효과는 파인 오일만 단독 처리한 경우 발병률 79.1%와 방제 효과 7.4%로 나타났지만 파인 오일과 수산화동을 4:1로 혼용 처리하였을 때 발병률 49.9%와 방제 효과 41.7%로 가장 효과적이었다. 이상의 결과는 고추의 세균성 점무늬병과 탄저병의 발병을 파인 오일과 수산화동을 4:1로 혼용 처리함으로서 친환경적으로 방제할 수 있음을 나타낸다. This research was performed to examine the protective activities of the mixtures of pine oil and copper hydroxide against bacterial spot and anthracnose on pepper plants. As for bacterial spot, the treatment of pine oil alone displayed high disease incidence (59.6%) and low protective effect (28.9%). In comparison, the treatments of mixtures and copper hydroxide alone showed protective activities of 66.8-76.1%. The mixture of pine oil and copper hydroxide (4:1) suppressed the most effectively bacterial spot on pepper. On the other hand, the mixture of pine oil and copper hydroxide (4:1) also showed the strongest protective effect against pepper anthracnose among the 4 treatments tested; its disease incidence and disease control value were 49.8% and 41.7%, respectively. The other treatments showed low protective activities with control values of 7.4-17.1%. These results suggested that the mixture of pine oil and copper hydroxide (4:1) can be used for the environmental-friendly disease control of bacterial spot and anthracnose on pepper.

Development of a Model to Predict the Primary Infection Date of Bacterial Spot (Xanthomonas campestris pv. vesicatoria) on Hot Pepper.

A population model of bacterial spot caused by Xanthomonas campestris pv. vesicatoria on hot pepper was developed to predict the primary disease infection date. The model estimated the pathogen population on the surface and within the leaf of the host based on the wetness period and temperature. For successful infection, at least 5,000 cells/ml of the bacterial population were required. Also, wind and rain were necessary according to regression analyses of the monitored data. Bacterial spot on the model is initiated when the pathogen population exceeds 1015 cells/g within the leaf. The developed model was validated using 94 assessed samples from 2000 to 2007 obtained from monitored fields. Based on the validation study, the predicted initial infection dates varied based on the year rather than the location. Differences in initial infection dates between the model predictions and the monitored data in the field were minimal. For example, predicted infection dates for 7 locations were within the same month as the actual infection dates, 11 locations were within 1 month of the actual infection, and only 3 locations were more than 2 months apart from the actual infection. The predicted infection dates were mapped from 2009 to 2012; 2011 was the most severe year. Although the model was not sensitive enough to predict disease severity of less than 0.1% in the field, our model predicted bacterial spot severity of 1% or more. Therefore, this model can be applied in the field to determine when bacterial spot control is required.

Control of Bacterial Spot of Tomato and Activation of Enzymes Related to Resistance by Chemicals Under Field Conditions

The control of tomato bacterial spot by the application of chemicals was evaluated on field condition during two trials. Thirty days after transplanting and every 14 days the tomato plants PA-529 hybrid were sprayed with acibenzolar-S-methyl (2.5 g 100 L-1), fluazinam (25 g 100 L-1), pyraclostrobin (8 g 100 L-1), pyraclostrobin + metiram (20 g 100 L-1 + 220 g 100 L-1), copper oxychloride (25.20 g 100 L-1), mancozeb + copper oxychloride (88 g 100 L-1 + 60 g 100 L-1), oxytetracycline (40 g 100 L-1) and water (control), totaling five applications during the crop cycle. Forty days after transplanting, the plants were inoculated with a Xanthomonas perforans isolate (107 UFC mL-1), disease severity was assessed (10, 19, 29, and 36 days after inoculation), and the area under the disease progress curve was calculated. All chemicals controlled the disease, but better results for total mass and number of fruit was obtained for fluazinam, pyraclostrobin, pyraclostrobin + metiram, copper oxychloride, and mancozeb + copper oxychloride in the first trial, and pyraclostrobin and pyraclostrobin + metiram in the second trial. The average fruit weight, °Brix, pH and total acidity were not affected by the application of the chemicals. The enzymatic activity of the polyphenol oxidase and peroxidase was higher in the first trial, but in the second, only the polyphenoloxidase had the highest activity in the treatments with acibenzolar-S-methyl, pyraclostrobin, and pyraclostrobin + metiram on tomato leaves. Products containing pyraclostrobin increased the activity of some enzymes without reducing the productivity.

Biological control of bacterial spot on peach by nonpathogenic Xanthomonas campestris strains AZ98101 and AZ98106

A suspension of nonpathogenic Xanthomonas campestris (nXc) strain AZ98101 or AZ98106 was sprayed on peach trees in biological control tests against bacterial spot caused by Xanthomonas arboricola pv. pruni. Treatment with each strain reduced the number of leaves with spots. Meta-analysis of the results from seven field trials showed an integrated risk ratio (the ratio of leaf spot incidence on inoculated leaves to incidence on control leaves) of 0.46 by treatment with AZ98101 and 0.54 by AZ98106, indicating that leaf spot incidence was significantly reduced by each strain. Each also significantly reduced the incidence of fruit spot. The risk ratio with AZ98101 was significantly lower than that with AZ98106. The population of AZ98101R-1, a rifampicin-resistant mutant of AZ98101, was 6.3 × 103 CFU/g (fresh mass) on leaves and 8.0 × 103 CFU/g on fruit at 12 days after inoculation, but was undetectable (<102 CFU/g) by 24 days. This is the first report that nXc strains AZ98101 and AZ98106 effectively control bacterial spot on peach.

Controle químico da mancha-bacteriana do tomate para processamento industrial em campo

Com o objetivo de avaliar produtos químicos no controle da mancha-bacteriana em tomate para processamento industrial, foram conduzidos dois ensaios na área experimental da Unilever Bestfoods, em Goiânia-GO. No primeiro, o híbrido Heinz 9992 foi inoculado com Xanthomonas perforans em blocos casualizados, com 15 tratamentos e três repetições. O segundo ensaio foi em blocos ao acaso com parcelas subdivididas com três repetições. A parcela principal foi "tratamento químico" (10 tratamentos) e a subparcela "híbrido" (Hypeel 108 e U2006). Inoculou-se X. perforans e X. gardneri. Em ambos os ensaios os produtos testados, em diferentes números de aplicações e regimes, foram: acibenzolar-S-metil (ASM); famoxadona + mancozebe; metiram + piraclostrobina; fosfito PK; cloretos de benzalcônio; óxido cuproso e hidróxido de cobre (SC, WP e WG). Em ambos os ensaios, foram avaliados severidade da doença nas folhas, número de frutos com sintomas e produtividade. No segundo ensaio avaliou-se também o número de frutos com escaldadura. No primeiro ensaio foram detectadas diferenças significativas (p&gt;0,05) entre os tratamentos somente nas duas primeiras avaliações de severidade, mas nenhum dos tratamentos diferiu da testemunha. No segundo ensaio, para severidade foliar, foi detectada diferença significativa apenas para os híbridos na primeira avaliação. Para número de frutos com sintomas e escaldadura a interação entre os fatores "tratamento químico" e "híbrido" foi também significativa. Nas folhas, 'U2006' foi mais resistente do que 'Hypeel 108', que apresentou maior incidência de escaldadura, mas nos frutos ocorreu o inverso. Para produtividade, os dois fatores foram significativos. 'U2006' foi mais produtivo do que 'Hypeel 108'. Entre os 10 tratamentos químicos, apesar de nenhum ter diferido da testemunha, famoxadona + mancozebe, que resultou em maior produtividade, diferiu de hidróxido de cobre (WG), ASM - famoxadona + mancozebe e cloretos de benzalcônio. ASM e famoxadona + mancozebe foram os que promoveram uma relação benefício/custo superior a 1.

Photocatalysis: Effect of Light-Activated Nanoscale Formulations of TiO2 on Xanthomonas perforans and Control of Bacterial Spot of Tomato

Protection of crops from bacterial diseases presents a continuing challenge, mandating the development of novel agents and approaches. Photocatalysis is a process where chemically reactive oxygen species are catalytically generated by certain minerals in the presence of light. These reactive oxygen species have the capacity to destroy organic molecular structures critical to pathogen viability. In this study, the antibacterial potential of photocatalytic nanoscale titanium dioxide (TiO(2)), nanoscale TiO(2) doped (incorporation of other materials into the structure of TiO(2)) with silver (TiO(2)/Ag), and nanoscale TiO(2) doped with zinc (TiO(2)/Zn; AgriTitan) was evaluated against Xanthomonas perforans, the causal agent for bacterial spot disease of tomato. In vitro experiments on photocatalytic activity and dose dependency were conducted on glass cover slips coated with the nanoscale formulations by adding a known population of X. perforans strain Xp-F7 and illuminating the cover slips under a visible light source. TiO(2)/Ag and TiO(2)/Zn had high photocatalytic activity against X. perforans within 10 min of exposure to 3 × 10(4) lux. Greenhouse studies on naturally and artificially infected transplants treated with TiO(2)/Zn at ≈500 to 800 ppm significantly reduced bacterial spot severity compared with untreated and copper control. Protection was similar to the grower standard, copper + mancozeb. The use of TiO(2)/Zn at ≈500 to 800 ppm significantly reduced disease incidence in three of the four trials compared with untreated and copper control, and was comparable to or better than the grower standard. The treatments did not cause any adverse effects on tomato yield in any of the field trials.

POLYSACCHARIDES FROM ALOE BARBADENSIS REDUCE THE SEVERITY OF BACTERIAL SPOT AND ACTIVATE DISEASE-RELATED PROTEINS IN TOMATO

Bacterial spot is an important disease of tomato that causes a reduction of the leaf area and affects plant yield. The objective of this study was to evaluate the effect of polysaccharides from aloe vera (Aloe barbadensis Miller) parenchyma (PAV) on the severity of bacterial spot and to detect the defense mechanisms activated by them. Tomato plants at the five true leaf stage were treated with PAV, and inoculated with Xanthomonas gardneri four days later. The effect of heating PAV suspension on its effectiveness for disease control was also evaluated. The ability of the polysaccharides to induce the synthesis of pathogenesis-related proteins in plants was determined spectrophotometrically. Finally, the antimicrobial effect of PAV on X. gardneri cultures was checked. PAV heated at 100°C for 30 min reduced bacterial spot severity by up to 85.1%, but control level was decreased when the PAV heating time was doubled. Concerning peroxidase, polyphenoloxidase, and glucanase activities in tomato plants treated with PAV, a significant increase of these enzymes was found, even before challenging plants with X. gardneri. Although PAV showed little direct effect on the bacteria it seems to constitute a good alternative for the control of bacterial spot of tomato through induced resistance.

Evolutionary and experimental assessment of novel markers for detection of Xanthomonas euvesicatoria in plant samples.

BackgroundBacterial spot-causing xanthomonads (BSX) are quarantine phytopathogenic bacteria responsible for heavy losses in tomato and pepper production. Despite the research on improved plant spraying methods and resistant cultivars, the use of healthy plant material is still considered as the most effective bacterial spot control measure. Therefore, rapid and efficient detection methods are crucial for an early detection of these phytopathogens.MethodologyIn this work, we selected and validated novel DNA markers for reliable detection of the BSX Xanthomonas euvesicatoria (Xeu). Xeu-specific DNA regions were selected using two online applications, CUPID and Insignia. Furthermore, to facilitate the selection of putative DNA markers, a customized C program was designed to retrieve the regions outputted by both databases. The in silico validation was further extended in order to provide an insight on the origin of these Xeu-specific regions by assessing chromosomal location, GC content, codon usage and synteny analyses. Primer-pairs were designed for amplification of those regions and the PCR validation assays showed that most primers allowed for positive amplification with different Xeu strains. The obtained amplicons were labeled and used as probes in dot blot assays, which allowed testing the probes against a collection of 12 non-BSX Xanthomonas and 23 other phytopathogenic bacteria. These assays confirmed the specificity of the selected DNA markers. Finally, we designed and tested a duplex PCR assay and an inverted dot blot platform for culture-independent detection of Xeu in infected plants.SignificanceThis study details a selection strategy able to provide a large number of Xeu-specific DNA markers. As demonstrated, the selected markers can detect Xeu in infected plants both by PCR and by hybridization-based assays coupled with automatic data analysis. Furthermore, this work is a contribution to implement more efficient DNA-based methods of bacterial diagnostics.

Antibacterial activity of essential oils on Xanthomonas vesicatoria and control of bacterial spot in tomato

The objective of this work was to evaluate the effects of plant essential oils (EOs) on the growth of Xanthomonas vesicatoria, on bacterial morphology and ultrastructure, and on the severity of tomato bacterial spot. EOs from citronella, clove, cinnamon, lemongrass, eucalyptus, thyme, and tea tree were evaluated in vitro at concentrations of 0.1, 1.0, 10, and 100% in 1.0% powdered milk. The effect of EOs, at 0.1%, on the severity of tomato bacterial spot was evaluated in tomato seedlings under greenhouse conditions. The effects of citronella, lemongrass, clove, and tea tree EOs, at 0.1%, on X. vesicatoria cells were evaluated by transmission electron microscopy. All EOs showed direct toxic effect on the bacteria at a 10%-concentration in vitro. Under greenhouse conditions, the EOs of clove, citronella, tea tree, and lemongrass reduced disease severity. EOs of clove and tea tree, and streptomycin sulfate promoted loss of electron-dense material and alterations in the cytoplasm, whereas EO of tea tree promoted cytoplasm vacuolation, and those of citronella, lemongrass, clove, and tea tree caused damage to the bacterial cell wall. The EOs at a concentration of 0.1% reduce the severity of the disease.

The role of cymoxanil and famoxadone in the management of bacterial spot on tomato and pepper and bacterial leaf spot on lettuce

Cymoxanil and famoxadone, the components of Tanos 50DF ® (25% a.i. of each product, E.I. du Pont de Nemours and Company, Wilmington, DE) were evaluated alone, together, and in combination with copper hydroxide and/or mancozeb for the control of bacterial spot on tomato and pepper, and bacterial leaf spot on lettuce. Neither Tanos nor its components alone had in vitro inhibitory activity against the copper-insensitive and copper-sensitive species of Xanthomonas evaluated. However, there was a synergistic interaction between copper hydroxide and Tanos in reducing the growth of a copper-resistant strain of Xanthomonas perforans. It appears that both components of Tanos are required for synergism since the addition of only cymoxanil or famoxadone to copper hydroxide did not induce significant reduction of bacterial populations in comparison to copper hydroxide alone. Increased disease control was not obtained on plants in greenhouse trials. In most of the greenhouse trials, the mixture of copper hydroxide and mancozeb combined with Tanos tended to induce similar level of disease control in comparison to different mixtures containing copper hydroxide, cymoxanil and famoxadone indicating that mancozeb might not be necessary in the management of copper-tolerant strains of Xanthomonads.

Chitosan Reduces Bacterial Spot Severity and Acts in Phenylpropanoid Metabolism in Tomato Plants

AbstractChitosan has recently shown potential for the control of plant diseases and can act as an elicitor in the induction of defence mechanisms. This study was made to assess the effect of chitosan on bacterial spot control caused by Xanthomonas gardneri in tomato plants. The chitosans used were commercial (Ccom), low molecular weight (Clmw) and medium molecular weight (Cmmw). Chitosans provided disease protection of up to 56%, with best results from Clmw at 3 mg/ml, applied 3 days prior to bacterial inoculation. The spectrophotometric profile of tomato plants that were treated with Clmw showed an increase of absorbance between wavelengths 280 and 300 mm, indicating that the polysaccharide may have induced the plants into synthesizing different compounds as a response to X. gardneri. The analysis of total phenolic compounds and flavonoids supported the results obtained in spectrophotometric scanning, showing a significant increase of those metabolites 3 days after inoculation. Therefore, chitosan has the capability of controlling bacterial spot in tomato plants, which is thought to be attributable to the induction of defence mechanisms in the plant.

Comparison of Kasugamycin to Traditional Bactericides for the Management of Bacterial Spot on Tomato

Studies were conducted at three locations in Florida to evaluate the effects of kasugamycin alone, in alternation, or as a tank-mix partner with copper bactericides and other fungicides against bacterial spot of tomato. In greenhouse trials, kasugamycin, formulated as Kasumin® 2L, reduced bacterial spot severity by up to 37.5% compared with a non-treated control. Little advantage in disease control was observed by mixing kasugamycin with other fungicides. Kasugamycin was assessed in six field trials. In the four field trials that tested kasugamycin alone, it was as effective as the standard copper + mancozeb treatment for the control of bacterial spot. In four trials, no benefit was observed in applying kasugamycin as a mixture with copper + mancozeb, and only one of three trials did alternating kasugamycin with copper + mancozeb improve bacterial spot control over either the copper + mancozeb standard or kasugamycin alone. Although kasugamycin was effective for the control of bacterial spot in greenhouse and field trials, rapid development of resistance in field populations of X. perforans may shorten the effective use of this antibiotic.

Influence of Shoot Pruning on Bacterial Spot Infestation on Tomato Cultivars

Field studies were conducted in Florida to determine the effect of early shoot pruning on the severity of bacterial spot, and on the growth and yield of different tomato (Solanum lycopersicum) cultivars. Two tomato cultivars, two inoculation regimes of bacterial spot pathogen (Xanthomonas perforans), and three shoot pruning programs were arranged in a split-split plot design. The tomato cultivars were Tygress and Security-28; shoot pruning included none, light, and heavy; and X. perforans treatments consisted of non-inoculated plots and plots inoculated with a suspension of the pathogen. Tomato plant height was not influenced by any of the three factors or their interactions, whereas the disease severity was higher in inoculated plots versus non-inoculated plants. Early extra-large fruit weight was affected by tomato cultivars and the inoculation with the bacterial spot pathogen, but not by pruning programs or the interaction among factors. Tomato plants inoculated with X. perforans reduced their extra-large fruit weight by 31% in comparison with non-inoculated plants. There were no differences on early marketable fruit weight among the combinations of each cultivar and the three pruning programs. All three factors individually influenced the seasonal marketable fruit weight of tomato, with no difference between light-pruned plants and the non-pruned control for seasonal marketable fruit weight, regardless of tomato cultivars. However, heavy pruning did reduce seasonal yields by 10% in comparison with the non-pruned control. These results indicated that light shoot pruning, which is the standard grower practice in Florida, did not improve bacterial spot control or tomato yields of total and extra-large marketable fruit, which might save up to $50/acre in reduced labor costs for Florida tomato growers.

Eficiência de argila silicatada no controle de Xanthomonas axonopodis pv. passiflorae, in vitro e em mudas de maracujazeiro-amarelo

A mancha bacteriana do maracujá, causada pela bactéria Xanthomonas axonopodis pv. passiflorae, ocorre em todas as regiões produtoras do País, sendo responsável por grandes perdas econômicas na cultura do maracujazeiro-amarelo. O presente trabalho teve como objetivos testar a eficiência de argila silicatada na inibição da bactéria X. axonopodis pv. passiflorae in vitro e no controle preventivo e curativo da mancha bacteriana em mudas de maracujazeiro-amarelo. A argila silicatada foi adicionada ao meio de cultura batata-dextrose-ágar fundente, nas concentrações de 0,0; 0,5; 1,0; 1,5 e 2,0%; vertido em placas de Petri. Após resfriamento do meio, repicou-se a suspensão bacteriana (10(7) UFC.mL-1) com uma alça, incubando-se as placas a 28 °C por três dias, quando se avaliou o crescimento bacteriano. Posteriormente, o produto, nas mesmas concentrações citadas, foi pulverizado em mudas de maracujá 'Afruvec' de forma preventiva ou curativa. A inoculação da bactéria foi realizada através de pulverização foliar da suspensão bacteriana (10(7) UFC.mL-1), 24 h antes ou após os tratamentos curativo e preventivo, respectivamente. A severidade da doença foi avaliada com auxílio de uma escala diagramática nas quatro primeiras folhas verdadeiras contadas de baixo para cima. Nas concentrações avaliadas, a argila silicatada inibiu a bactéria in vitro e os sintomas da mancha bacteriana no tratamento curativo, enquanto no tratamento preventivo, controle significativo foi obtido a partir de 1,0% de argila silicatada. Com base nestes resultados, a argila silicada pode ser recomendada, na concentração de 1,0-2,0%, para o controle da mancha bacteriana do maracujazeiro em pulverizações foliares.

Phytotoxicity of Copper-Based Bactericides to Peach and Nectarine.

Organometallic copper, consisting of a mixture of copper abietate, copper linoleate, and copper oleate (CuALO), is important for postbloom management of bacterial spot in New Jersey peach and nectarine orchards. Rotation of CuALO with oxytetracycline reduces cost and helps prevent (or delay) resistant organisms. However, because copper is also phytotoxic, higher rates and inorganic coppers have not been utilized. A study was conducted on 'Encore' peach and 'Redgold' nectarine to determine the quantitative relationship between copper concentration (metallic equivalent) and phytotoxicity. Different rates of CuALO and copper hydroxide (CuOH) were applied seven times postbloom. Foliar injury and defoliation increased with number of applications and copper concentration. Maximum 'Encore' defoliation was 10 to 17%, while 'Redgold' sustained 30 to 35% leaf loss. CuOH caused similar or less leaf injury and defoliation than CuALO. No injury was observed on fruit, even at three times the labeled metallic copper rate of CuALO. Fruit size and soluble solids were not influenced by copper. Estimates of foliar density and tree volume indicated that sufficient photosynthetic capacity existed to allow acceptable leaf damage and loss from copper applications. These results showed that inorganic coppers may be viable alternatives to organometallic copper for postbloom bacterial spot control; nectarine may be more sensitive to copper injury than peach; and higher rates of metallic copper, above the current commercial rate, can be applied to peach. In the latter case, greater amounts of copper may provide longer residual activity and improved bacterial spot control on highly susceptible cultivars.

Biological control of bacterial spot of tomato using hrp mutants of Xanthomonas campestris pv. vesicatoria

Abstract Xanthomonas campestris pv. vesicatoria strain 75-3 hrpG , hrpX , hrpF and hrpE1 mutants were evaluated for control of bacterial spot of tomato under both greenhouse and field conditions. In greenhouse studies, the 75-3 hrp mutants were spray-inoculated onto tomato foliage 48 h prior to inoculation of the wild-type pathogen, X. campestris pv. vesicatoria 75-3, and bacterial spot severity was assessed 10 days after pathogen inoculation. Statistically significant reductions in disease severity relative to the buffer treatment were provided by all four 75-3 hrp mutants. Unexpectedly, however, disease reductions differed significantly among the mutants with the 75-3S hrpG mutant consistently providing the greatest disease suppression (mean reduction in disease severity compared to the buffer treatment of ∼58%), followed by the hrpX mutant (mean ∼40%), the hrpF mutant (mean ∼30%), and the hrpE1 mutant, which provided the least control (mean ∼21%). Disease control efficacy of these mutants was evaluated under field conditions in Alabama (AL) and Florida (FL). Only the 75-3S hrpG mutant and the 75-3 hrpF mutant provided statistically significant reductions in disease severity compared to the pathogen-only control in all three field trials. In the two AL trials, the 75-3S hrpG mutant was significantly more effective in reducing bacterial spot severity than the previously most effective biological control agents Pseudomonas syringae Cit7 and Pseudomonas putida B56. In the two AL trials, the 75-3S hrpG was as effective as the plant activator acibenzolar- S -methyl in one experiment but less effective in the other experiment. Averaged across all three field trials the 75-3S hrpG mutant provided a mean reduction in foliar disease severity of ∼76%, compared to the mean of ∼29% for P. syringae Cit7 averaged across all previous field trials. This study is significant not only for the selection of a biological control agent superior to previously selected strains and comparable in efficacy to the plant activator acibenzolar- S -methyl, but also for the finding that not all hrp mutants of a given bacterial strain are equally effective as biological control agents of that pathogen.

Effect of acidic electrolyzed water on the viability of bacterial and fungal plant pathogens and on bacterial spot disease of tomato

Acidic electrolyzed water (AEW), known to have germicidal activity, was obtained after electrolysis of 0.045% aqueous solution of sodium chloride. Freshly prepared AEW (pH 2.3-2.6, oxidation-reduction potential 1007-1025 mV, and free active chlorine concentration 27-35 ppm) was tested in vitro and (or) on tomato foliage and seed surfaces for its effects on the viability of plant pathogen propagules that could be potential seed contaminants. Foliar sprays of AEW were tested against bacterial spot disease of tomato under greenhouse and field conditions. The viability of propagules of Xanthomonas campestris pv. vesicatoria (bacterial spot pathogen), Streptomyces scabies (potato scab pathogen), and Fusarium oxysporum f.sp. lycopersici (root rot pathogen) was significantly reduced 4-8 log units within 2 min of exposure to AEW. Immersion of tomato seed from infected fruit in AEW for 1 and 3 min significantly reduced the populations of X. campestris pv. vesicatoria from the surface of the seed without affecting seed germination. Foliar sprays of AEW reduced X. campestris pv. vesicatoria populations and leaf spot severity on tomato foliage in the greenhouse. In the field, multiple sprays of AEW consistently reduced bacterial spot severity on tomato foliage. Disease incidence and severity was also reduced on fruit, but only in 2003. Fruit yield was either enhanced or not affected by the AEW sprays. These results indicate a potential use of AEW as a seed surface disinfectant or contact bactericide.

Efeito de produtos químicos e biológicos sobre a mancha bacteriana, flora microbiana no filoplano e produtividade de pimentão

Avaliou-se o efeito de pulverizações semanais com sulfato de estreptomicina + oxitetraciclina (0,8 g ia L-1), oxicloreto de cobre (2,4 g ia L-1), biofertilizante Agrobio (5%), e testemunha (água) sobre o controle da mancha-bacteriana, sobre a flora microbiana no filoplano e sobre a produtividade de três cultivares de pimentão (Magda, Cascadura Itaipu e Magali R). Os experimentos foram realizados em campo de maio a outubro de 2002. Adotou-se o delineamento de blocos ao acaso, em esquema fatorial (4x3), com quatro repetições. Realizaram-se avaliações semanais, durante três meses para altura de plantas (cm); número de hastes; número total de folhas; número de folhas caídas; incidência de folhas lesionadas; severidade da mancha bacteriana e produtividade (t ha-1). Paralelamente, quantificou-se a população microbiana residente no filoplano e nos frutos. Não houve efeito dos tratamentos sobre a produção de frutos, porém, observou-se efeito sobre o desenvolvimento vegetativo das plantas, sobre a mancha bacteriana e sobre a flora microbiana no filoplano. O oxicloreto de cobre inibiu o desenvolvimento vegetativo, a taxa de abscisão foliar e a flora bacteriana no filoplano. O Agrobio favoreceu o desenvolvimento vegetativo e, assim como o sulfato de estreptomicina + oxitetraciclina, reduziu a população de bactérias, exceto de Bacillus sp., e de fungos, exceto Cladosporium sp., no filoplano. O híbrido Magali R foi significativamente superior às demais cultivares quanto ao vigor das plantas, produtividade e resistência à mancha bacteriana. Estes resultados sugerem atividade bactericida do Agrobio em condições de campo.

Integrated biological control of bacterial speck and spot of tomato under field conditions using foliar biological control agents and plant growth-promoting rhizobacteria

Integration of foliar bacterial biological control agents and plant growth promoting rhizobacteria (PGPR) was investigated to determine whether biological control of bacterial speck of tomato, caused by Pseudomonas syringae pv. tomato, and bacterial spot of tomato, caused by Xanthomonas campestris pv. vesicatoria and Xanthomonas vesicatoria, could be improved. Three foliar biological control agents and two selected PGPR strains were employed in pairwise combinations. The foliar biological control agents had previously demonstrated moderate control of bacterial speck or bacterial spot when applied as foliar sprays. The PGPR strains were selected in this study based on their capacity to induce resistance against bacterial speck when applied as seed and soil treatments in the greenhouse. Field trials were conducted in Alabama, Florida, and California for evaluation of the eYcacy in control of bacterial speck and in Alabama and Florida for control of bacterial spot. The foliar biological control agent P. syringae strain Cit7 was the most eVective of the three foliar biological control agents, providing signiWcant suppression of bacterial speck in all Weld trials and bacterial spot in two out of three Weld trials. When applied as a seed treatment and soil drench, PGPR strain Pseudomonas Xuorescens 89B-61 signiWcantly reduced foliar severity of bacterial speck in the Weld trial in California and in three of six disease ratings in the Weld trials in Alabama. PGPR strains 89B-61 and Bacillus pumilus SE34 both provided signiWcant suppression of bacterial spot in the two Weld trials conducted in Alabama. Combined use of foliar biological control agent Cit7 and PGPR strain 89B-61 provided signiWcant control of bacterial speck and spot of tomato in each trial. In one Weld trial, control was enhanced signiWcantly with combined biological control agents compared to single agent inoculations. These results suggest that some PGPR strains may induce plant resistance under Weld conditions, providing eVective suppression of bacterial speck and spot of tomato, and that there may be some beneWt to the integration of rhizosphere-applied PGPR and foliar-applied biological control agents.

Biological control of bacterial spot of tomato caused by Xanthomonas campestris pv. vesicatoria by Rahnella aquatilis

Xanthomonas campestris pv. vesicatoria strain 2 was isolated from infected tomato seedlings grown in open field in Egypt. This strain produced irregular yellow-necrotic areas on tomato leaves and spotting of the stem. In an attempt to control this disease biologically, four experiments were conducted and tomato seedlings were pretreated, before the pathogen, with either of two antagonistic strains of Rahnella aquatilis through leaves, roots, soil or seeds. In all experiments, seedlings pretreated with R. aquatilis showed reduced susceptibility toward X. c. pv. vesicatoria. They also contained reduced protein concentration and showed reduced number of protein bands in SDS-PAGE analysis as well as increased fresh and dry weight relative to control seedlings inoculated with the pathogen only. This indicates that R. aquatilis reduced the deleterious effect and the stress exerted by X. c. pv. vesicatoria on tomato seedlings. Foliar application of R. aquatilis was the most effective method in disease reduction which could be attributed to the direct effect of the antagonistic bacteria on the pathogen. The highest amounts of fresh and dry weight were obtained from seed treatment, which might suggest that bacterial seed inoculation provides earlier protection than could be achieved with foliar, soil or root treatment.