Bacterial Spot Severity Research Articles

Nanopartículas de Simonkolleite no tratamento de sementes e controle da mancha bacteriana do tomateiro causada por Xanthomonas hortorum pv. gardneri

ABSTRACT Bacterial spot caused by Xanthomonas spp. (X. vesicatoria, X. euvesicatoria pv. euvesicatoria, X. euvesicatoria pv. perforans, and X. hortorum pv. gardneri) may result in significant losses for tomato crops. Simonkolleite nanoparticles (SK-NPs) has been indicated as a novel approach for plant disease control. The objective of this work was to evaluate SK-NPs (ZnOCl, ZnOCl:Ag, and ZnOCl:Cu at different concentrations) for the in vitro inhibition of X. hortorum pv. gardneri, determining the time of exposure of the products for the bacterial death; the reduction of bacteria recovery on inoculated seeds, and their efficacy to reduce bacterial spot severity in plant. The growth inhibition was evaluated by inhibition zone in culture medium plates, when the diameter of the inhibition zone was measured. The period of exposure of the products to the bacterial suspension tested were 1, 2, 3, 4, or 5 h. Tomato inoculated seeds were treated with SK-NPs. In plant, the preventive and curative effects were evaluated by applying the products two days before or after inoculation, respectively. Disease severity was evaluated and the area under the disease progress curve (AUDPC) was calculated. ZnOCl:Ag, ZnOCl:Cu, and ZnOCl inhibited bacterial growth, and the 5 h exposure time was necessary to reduce bacterial growth. ZnOCl:Ag, and ZnOCl:Cu reduced the bacteria presence in the seeds, and did not affect the seed germination. Both products reduced the AUDPC in the preventive application. The use of SK-NPs ZnOCl:Ag and ZnOCl:Cu showed to be promising to manage tomato bacterial spot.

Optimizing the application of acibenzolar-S-methyl and copper to control bacterial spot on fresh-market tomato

This study aimed to adjust the number of applications of acibenzolar-S-methyl (ASM) and copper in an integrated program for the control of bacterial spot on fresh-market tomato. Two field trials were carried out during 2018 and 2019. Four sets of number of weekly applications of ASM were evaluated (7, 9, 11, and 13 applications). In addition to these, four other treatments were included: two as a tank mixture compound [13 weekly applications of ASM + biostimulant and nine applications of ASM + copper oxychloride]. Copper oxychloride was applied after ASM treatments in order to complete 13 applications per growing season. Copper oxychloride and untreated plots were used as a control. The variables evaluated were bacterial spot severity, total yield, and yield per classes of fruit according to the Brazilian market standards. Benefit-cost ratio (B/C) was calculated considering the income increase of a given treatment in relation to the untreated control. The disease ratings and yield data were subjected to ANOVA and the means tested for significance by Fisher, Dunnett, and orthogonal contrasts comparison tests. Regression analysis were carried out with the disease ratings to evaluate the ASM number of applications. As the number of ASM applications increased, disease severity decreased, although, the best B/C was obtained with seven applications of ASM, followed by copper applications until the end of the cycle. The tank mixture compound treatments did not result in economic gain increase. Moreover, disease severity was significantly high when ASM was applied in tank mixture with copper.

Transcriptome-wide modulation by Sargassum vulgare and Acanthophora spicifera extracts results in a prime-triggered plant signalling cascade in tomato and sweet pepper.

Seaweed extracts (SWEs) are becoming integrated into crop production systems due to their multiple beneficial effects including growth promotion and induction of defence mechanisms. However, the comprehensive molecular mechanisms of these effects are yet to be elucidated. The current study investigated the transcriptomic changes induced by SWEs derived from Sargassum vulgare and Acanthophora spicifera on tomato and sweet pepper plants. Tomato and sweet pepper plants were subjected to foliar treatment with alkaline extracts prepared from the above seaweeds. Transcriptome changes in the plants were assessed 72 h after treatments using RNA sequencing. The treated plants were also analysed for defence enzyme activities, nutrient composition and phytohormonal profiles. The results showed the significant enrichment of genes associated with several growth and defence processes including photosynthesis, carbon and nitrogen metabolism, plant hormone signal transduction, plant-pathogen interaction, secondary metabolite metabolism, MAPK signalling and amino acid biosynthesis. Activities of defence enzymes were also significantly increased in SWE-treated plants. Plant nutrient profiling showed significant increases in calcium, potassium, nitrogen, sulphur, boron, copper, iron, manganese, zinc and phosphorous levels in SWE-treated plants. Furthermore, the levels of auxins, cytokinins and gibberellins were also significantly increased in the treated plants. The severity of bacterial leaf spot and early blight incidence in plants treated with SWE was significantly reduced, in addition to other effects like an increase in chlorophyll content, plant growth, and fruit yield. The results demonstrated the complex effect of S. vulgare and A. spicifera extracts on the plants' transcriptome and provided evidence of a strong role of these extracts in increasing plant growth responses while priming the plants against pathogenic attack simultaneously. The current study contributes to the understanding of the molecular mechanisms of SWEs in plants and helps their usage as a viable organic input for sustainable crop production.

Extracts and fractions of humic substances reduce bacterial spot severity in tomato plants, improve primary metabolism and activate the plant defense system

We evaluated the liquid vermicompost extracts and fractions of humic substances in biostimulus and bacterial spot control in tomato plants. Unfiltered crude extract of liquid vermicompost (UFCE), filtered crude extract (FCE), humic acid (HA) and fulvic acid (FA) were sprayed on tomato leaves before the Xanthomonas hortorum pv. gardneri inoculation. Plants sprayed with HA showed the lowest bacterial spot severity. Defense enzyme activity increased 3 times in plants treated with HA. HA were the most active fraction in promoting growth with greatest increases in roots biomass and nitrate reductase enzyme activity.

Peptide Conjugates Derived from flg15, Pep13, and PIP1 That Are Active against Plant-Pathogenic Bacteria and Trigger Plant Defense Responses.

ABSTRACTThirty peptide conjugates were designed by combining an antimicrobial peptide (BP16, BP100, BP143, KSL-W, BP387, or BP475) at the N- or C-terminus of a plant defense elicitor peptide (flg15, BP13, Pep13, or PIP1). These conjugates were highly active in vitro against six plant-pathogenic bacteria, especially against Xanthomonas arboricola pv. pruni, Xanthomonas fragariae and Xanthomonas axonopodis pv. vesicatoria. The most active peptides were those incorporating Pep13. The order of the conjugation influenced the antibacterial activity and the hemolysis. Regarding the former, peptide conjugates incorporating the elicitor peptide flg15 or Pep13 at the C-terminus were, in general, more active against Pseudomonas syringae pv. actinidiae and P. syringae pv. syringae, whereas those bearing these elicitor peptides at the N-terminus displayed higher activity against Erwinia. amylovora and the Xanthomonas species. The best peptide conjugates displayed MIC values between 0.8 and 12.5 μM against all the bacteria tested and also had low levels of hemolysis and low phytotoxicity. Analysis of the structural and physicochemical parameters revealed that a positive charge ranging from +5 to +7 and a moderate hydrophobic moment/amphipathic character is required for an optimal biological profile. Interestingly, flg15-BP475 exhibited a dual activity, causing the upregulation of the same genes as flg15 and reducing the severity of bacterial spot in tomato plants with a similar or even higher efficacy than copper oxychloride. Characterization by nuclear magnetic resonance (NMR) of the secondary structure of flg15-BP475 showed that residues 10 to 25 fold into an α-helix. This study establishes trends to design new bifunctional peptides useful against plant diseases caused by plant-pathogenic bacteria.IMPORTANCE The consequences of plant pathogens on crop production together with the lack of effective and environmentally friendly pesticides evidence the need of new agents to control plant diseases. Antimicrobial and plant defense elicitor peptides have emerged as good candidates to tackle this problem. This study focused on combining these two types of peptides into a single conjugate with the aim to potentiate the activity of the individual fragments. Differences in the biological activity of the resulting peptide conjugates were obtained depending on their charge, amphipathicity, and hydrophobicity, as well as on the order of the conjugation of the monomers. This work provided bifunctional peptide conjugates able to inhibit several plant-pathogenic bacteria, to stimulate plant defense responses, and to reduce the severity of bacterial spot in tomato plants. Thus, this study could serve as the basis for the development of new antibacterial/plant defense elicitor peptides to control bacterial plant pathogens.

Bacterial spot caused by Xanthomonas vesicatoria devastated tomato production of Khyber Pakhtunkhwa-Pakistan

In Khyber Pakhtunkhwa (KP) province-Pakistan, bacterial spot caused by Xanthomonas campestris pv. vesicatoria (Xcv) has decimated commercial tomato production. Field surveys were conducted in 2017 and 2018 to analyse the effects of the bacterial spot in tomato producing areas of KP, including Swat, Lower Dir, and Mansehra. During the growing seasons, diseased samples were collected from tomato fields, and disease incidence and severity were documented. The pathogen was isolated, purified, and morphologically and biochemically characterised. Most of the morphological and biochemical characteristics such as yellow colonies, were like those of Xanthomonas spp. Further, the pathogen was confirmed using XV1F/XV1R pair of species-specific primers, which amplify the atpD gene sequence solely in Xanthomonas vesicatoria. Out of 30 isolates, 16 isolates were confirmed to be Xcv. In these agro-ecological zones, this was the first report on the presence of Xcv. Furthermore, humidity and temperature were found to impact the incidence and severity of bacterial spot substantially. Most isolates grew at high temperatures and low humidity; however, some prefered high-temperature and low-humidity environments. In conclusion, bacterial spot disease caused by Xcv has now spread throughout all tomato-producing areas of KP province. To avert future plant epidemics, ongoing climate and pest monitoring is required to build an effective disease warning system for producers and other agriculture-related agencies.

Current Situation of Mango Bacterial Black Spot Caused by <i>Xanthomonas campestris</i> pv <i>mangiferaeindicae</i> in the Poro and Tchologo Regions in Côte d'Ivoire

Mango bacterial black spot is an emerging disease in Cote d'Ivoire and the damage caused is becoming more and more significant. This study aims at diagnosing bacterial black spot incidence and severity level in regions of intensive mango production. Surveys were carried out during the vegetative stage of mango trees from July to August 2019 and the fruiting stage from March to April 2020 in 50 orchards in the Poro and Tchologo regions. In each orchard, 5 mango trees regularly dispersed over an area of 0.5 ha were assessed. On each tree, three (3) twigs per cardinal point were selected then the leaves counted and the leaf area covered by bacterial black spot symptoms determined. At fruiting stage, bacterial black spot severity on 40 fruits per selected tree, at the rate of 10 fruits per cardinal point was assessed. Bacterial black spot symptoms were observed in all orchards and the bacterium, Xanthomonas campestris pv. Mangiferaeindicae, was systematically isolated basing on symptoms taken from the leaves and fruits collected. Statistical analysis of the mean incidence and severity per town revealed a variability of 83.2% up to 90% on the leaves and 41.42% up to 55% on the fruits regarding incidence. As for severity, the highest values, 10.58% and 5.23% on leaves and fruits respectively were recorded in the department of Tafiere. Mango bacterial black spot is found in orchards located in the Poro and Tchologo regions. Incidence and severity are strongly related to the humidity conditions of the production area.

Reaction of Sour Passion Fruit Lineages and Hybrids to Bacterial Spot Caused by Xanthomonas axononopodis pv. passiflorae Under Protected Cultivation and Field Conditions

Passion fruit is infected by many plant pathogens, including Xanthomonas axonopodis pv. passiflorae, causing bacterial spot disease. This disease has been impaired orchards all over Brazil, resulting in low yield and production. In addition, it results in premature death of plants in the field. This study aimed to analyze the reaction of sour passion fruit genotypes to bacterial spot in leaves under protected cultivation (Experiment 1) and the bacterial spot severity in fruits under field conditions (Experiment 2). Experiment 1 was carried out as a randomized block design (RBD) with subdivided plots, composed of 24 treatments (genotypes), three replications, five plants per plot, and five evaluation dates. Bacterial spot incidence and severity were evaluated using a 0 to 5 grading scale. Evaluations were carried out at a 7-day interval after disease symptoms first appeared. Genotypes differed for mean disease severity and incidence. The bacterial spot disease evaluations showed that genotypes MAR20#46 P3 R4 X Rosa Claro R4 and MD 16 P3 X MAR20#39 P1 R4 presented the lowest scores for the disease incidence in the leaves. S2L AP R1, MAR20#19 ROXO R4 X ECRAM P3 R3, and MD 16 P3 X MAR20#39 P1 R4 were the genotypes with the lowest disease severity scores. Experiment 2 consisted of a RBD with 24 treatments, three replications, and seven plants per plot. Severity assessments were monthly performed on five fruits per plot, totaling three evaluation dates. In this experiment, the percentage of total fruit area with necrotic lesions was measured using a 1 to 4 grading scale. Bacterial spot severity assessments in fruits identified interactions between genotypes and evaluation dates (p ≤ 0.05). The lineages S2L MAR 20#15 R4 and S2L MAR20#19 R2 showed the lowest mean severity scores of bacterial spot in fruit. The genotypes with the lowest mean scores were selected to continue the breeding program.

Prevalence of Bacterial Leaf Spot of Bottle Gourd and Pumpkin in Subtropical Zone of Himachal Pradesh

To assess the prevalence and severity of bacterial leaf spot on bottle gourd and pumpkin, a survey was conducted in Hamirpur, Una and Bilaspur districts of sub tropical zone of Himachal Pradesh, India during the years 2018 and 2019. Data were recorded in terms of disease severity and fruit rot incidence. The associated pathogen from bottle gourd and pumpkin was isolated on nutrient sodium chloride agar medium and identified on the basis of morphological, biochemical and pathogenicity tests on bottle gourd and pumpkin seedlings. Disease was found to be prevalent at all the locations surveyed exhibiting a mean disease severity from 24.70 to 87.55 and 5.30 to 52.92 per cent in bottle gourd and pumpkin, respectively. Fruits of bottle gourd were recorded to be affected badly exhibiting a mean fruit rot incidence of 10.23 to 95.32 to per cent, while, no fruit rot incidence was recorded in pumpkin fruits. The colonies of the isolated bacterium were mucoid, circular, smooth textured and yellow in colour having a diameter of 2-4 mm. The pathogen was found to be Gram–ve and tested positive for esculin hydrolysis as well as protein digestion test. During pathogenicity tests, incubation period of 2 and 4 days was recorded on bottle gourd and pumpkin, respectively. Based on these studies, the identity of the pathogen was confirmed to be Xanthomonas cucurbitae(ex Bryan) Vauterin et al.

Evaluation of a Small-Molecule Compound, N-Acetylcysteine, for the Management of Bacterial Spot of Tomato Caused by Copper-Resistant Xanthomonas perforans.

Bacterial spot caused by Xanthomonas spp. is one of the major diseases in tomato. Xanthomonas perforans is the main pathogen of bacterial spot on tomato in Florida. Currently, application of copper fungicides is the primary measure used to manage this disease. However, the development of copper resistance in X. perforans and accumulation of copper in the environment are major concerns for excessive use of copper-based products in agriculture. Due to its antibacterial properties and low environmental impact, N-acetylcysteine (NAC), a small molecule commonly used in medicine for human bacterial diseases, has been studied in agriculture for the control of plant bacterial pathogens, including X. citri and Xylella fastidiosa. This study evaluated the effect of NAC alone and in combination with copper on a copper-resistant X. perforans strain in vitro and its ability to control bacterial spot of tomato under greenhouse and field conditions. In vitro, the minimum inhibitory concentration of NAC against the X. perforans strain was 2,048 mg liter-1. NAC increased sensitivity of the copper-resistant X. perforans to copper in vitro when application of NAC was followed by copper application after 6 h. In greenhouse assays, NAC applied alone or in combination with copper significantly (P < 0.05) reduced the disease severity of bacterial spot on tomato compared with the untreated control. NAC at 100 mg liter-1 + copper at 300 mg liter-1 consistently exhibited synergistic effects against bacterial spot. In the field trials, NAC at 1,000 mg liter-1 + copper at 150 mg liter-1 significantly reduced disease severity compared with the untreated control. Results from this study demonstrated that NAC significantly reduced the disease severity of bacterial spot of tomato and enhanced the efficacy of copper against copper-resistant X. perforans, indicating that NAC could be applied for the effective management of bacterial spot of tomato.

Antibacterial effect of copper composites against Xanthomonas euvesicatoria

Bacterial spot disease caused by Xanthomonas euvesicatoria is one of the major constraints for pepper production in Florida and worldwide. The common prevalence of copper (Cu)-tolerant X. euvesicatoria strains has reduced the efficacy of Cu based bactericides against bacterial spot of pepper. In this study, we evaluated antimicrobial activity of three Cu-based nanocomposites, namely, core-shell Cu (CS–Cu), fixed-quat Cu (FQ-Cu) and mixed-valence Cu (MV-Cu), along with Kocide® 3000, which is a micron size metallic Cu bactericide and is commercially available, both in vitro and in greenhouse trials, against a Cu-tolerant strain of X. euvesicatoria. In repeated in vitro tests, X. euvesicatoria growth was completely inhibited 24 h after exposure of bacterial cells to 500 and 1000 μg/ml of MV-Cu and all concentrations of FQ-Cu and CS-Cu (100, 200, 500, and 1000 μg/ml) treated for 1 h. Micron size copper, even at 1000 μg/ml, had no statistical difference in growth in comparison to the untreated control (P = 0.05; LSD). In the repeated greenhouse experiments, plants treated with all the copper composites exhibited less bacterial spot severity than untreated control and similar or significantly less than Cu-mancozeb (P < 0.05). However, MV-Cu was the only Cu composite with no phytotoxicity on plants under controlled conditions. This study shows potential to use Cu-based nanoparticles for efficient management of bacterial spot on pepper.

Biocontrol of bacterial spot on tomato by foliar spray and growth medium application of Bacillus amyloliquefaciens and Trichoderma asperellum

To date, few studies have focused on the combined use of two biocontrol agents to manage bacterial spot on tomato. Thus, the goal of this study was to evaluate the effects of the combined and individual use of Bacillus amyloliquefaciens and Trichoderma asperellum on the nutrient contents of tomato plants and bacterial spot on tomato caused by Xanthomonas perforans. Tomato plants were treated with the foliar spray and growth medium application of B. amyloliquefaciens or T. asperellum or both. Plants treated with sterile water served as the uninoculated control, and a copper standard consisting of cupric hydroxide plus an ethylene bisdithiocarbamate (EBDC) fungicide was also included. The application methods used for B. amyloliquefaciens and T. asperellum significantly influenced the P, K, and Mg contents in tomato plants. All biocontrol treatments significantly reduced the final disease severity of bacterial spot on tomato by 25.6–56.0% and the area under the disease progress curve (AUDPC) by 33.9–57.2% compared with the untreated control. The application of either B. amyloliquefaciens or T. asperellum via growth medium produced statistically equivalent results in reducing the final disease severity compared with the standard, but the other biocontrol treatments were significantly better than the standard. Similarly, the application of either B. amyloliquefaciens or T. asperellum via growth medium produced statistically equivalent results in lowering the AUDPC compared with the standard. However, the other biocontrol treatments significantly reduced the AUDPC by 39.7–44.8% compared with the standard. In summary, both the combined use and individual application of B. amyloliquefaciens and T. asperellum via foliar spray or growth medium application or both have the potential to control bacterial spot on tomato.

Sugar maple autumn-shed leaf extract: a potential antibacterial agent for the management of lettuce bacterial leaf spot (Xanthomonas campestris pv. vitians) and varnish spot (Pseudomonas cichorii)

Different extracts prepared from wastes (barks, branches, needles, or leaves) of different trees (grey alder, balsam fir, American larch, red maple, sugar maple, white spruce, black spruce, jack pine, white pine, quaking aspen, sweet cherry, and northern red oak) were investigated for their potential use as antibacterial agents for the management of lettuce varnish spot and bacterial leaf spot caused by Pseudomonas cichorii (Swingle) Stapp and Xanthomonas campestris pv. vitians (Brown) Dye, respectively. Extracts were first screened for their antibacterial activities against P. cichorii and X. campestris pv. vitians using the in vitro disk diffusion assay. Based on the diameter of the inhibition zone, ethanol (95%) extract prepared from sugar maple autumn-shed leaves (SMASL) and aqueous ethanol (50%, v/v) extracts prepared from SMASL and from sugar maple green leaves showed the strongest antibacterial activities. Ethanol (95%) SMASL extract was further investigated for its efficacy to manage bacterial diseases when applied on lettuce plants grown in the greenhouse. Foliar application of ethanol (95%) SMASL extract at a concentration of 3.2 g L−1 was shown to significantly (P ≤ 0.05) reduce bacterial leaf spot severity compared with the control without causing phytotoxicity symptoms that could prevent the commercial marketing of the lettuce. Ethanol (95%) SMASL extract (1.6 and 3.2 g L−1) was also shown to significantly reduce varnish spot severity in one experiment out of two. This study identifies for the first time the possibility of exploiting SMASL to manage bacterial diseases affecting horticultural crops.

Screening of Sour Passion Fruit for Reaction to Bacterial Spot and Passion Fruit Woodiness Disease

The development of resistant varieties is a promising strategy for bacterial spot disease (Xanthomonas axonopodis pv. passiflorae-Xap) and passion fruit woodiness disease (PWD; Cowpea aphid-borne mosaic virus-CABMV) control in sour passion fruit (Passiflora edulis Sims). This study aimed at evaluating the reaction of 12 sour passion fruit half-sib progenies to both mechanically inoculated Xap and CABMV, under protected cultivation. The bacterial spot and PWD severity degrees observed reveal the existence of variability within progenies. MAR20#2005 and BRS GA1 revealed the lowest bacterial disease severity scores while MAR20#41, MAR20#2005, and Rosa Intenso 1 showed the lowest PWD severity scores. MAR20#41 presented the lowest disease incidence in all evaluations, demonstrating a slow increase in the number of plants with symptoms over time. Also, MAR20#41 stood out as the progeny with the greatest number of plants presenting resistance to PWD at the end of the study. Among the progenies selected, MAR20#2005 was the most promising for presenting the lowest severity scores for both bacterial spot and PWD.

Development and validation of a standard area diagram set as assessment aid for estimating the severity of bacterial spot on tri-lobed leaves of yellow passion fruit

Bacterial spot (Xanthomonas axonopodis pv. passiflorae) significantly reduces yellow passion fruit (Passiflora edulis Sims) yield and longevity. A standard area diagram set (SADs) for severity assessment of bacterial spot on tri-lobed leaves of yellow passion was developed and validated in this study. The SADs consisted of eight severity levels (2; 4; 9; 18; 35; 58; 80; and 94%). For its validation, 20 raters, who initially estimated the disease severity without the aid of the SADs, were divided into four groups (G1 and G3, inexperienced; G2 and G4, experienced). Subsequently, G1 and G2 performed the second evaluation without the SADs, and G3 and G4 completed the second evaluation with the proposed SADs. The accuracy and precision of the assessments were determined by simple linear regression and by the Lin’s concordance correlation coefficient (LCCC). The proposed SADs allowed accurate and precise quantification of bacterial spot severity, increasing the agreement between estimated and actual values. Inexperienced raters benefited the most from the use of the SADs. The increase in accuracy and precision in the non-aided groups, when present, was less pronounced than those increments observed in the SADs-aided groups. The LCCC confirmed the increases in accuracy and precision detected by the linear regression analysis.

Evaluation of a small molecule compound 3-indolylacetonitrile for control of bacterial spot on tomato

Bacterial spot, caused by Xanthomonas perforans, is one of the major diseases in fresh market tomato production in Florida. It is reported that X. perforans has developed resistance to copper, an element of major bactericides used for management of this disease in Florida and worldwide. Continuous efforts are necessary for providing the tomato industry with new effective approaches to managing this important disease. A small molecule 3-indolylacetonitrile (IAN) that can inhibit biofilm formation has been reported to be effective against many medical bacterial pathogens. In this study, we evaluated the efficacy of IAN in planta for the control of bacterial leaf spot on tomato, the effectiveness of IAN when applied at different times from pathogen inoculation, how IAN efficacy compared to a copper bactericide (Kocide 3000), and if IAN could be applied as a tank mixture with copper bactericide. In vitro testing in liquid media was also completed to further investigate observations made in planta. Our results showed that IAN was effective in reducing disease severity of bacterial leaf spot on tomato between 0.5 and 1.0 mg/ml. However, phytotoxicity to tomato plants occurred when the concentration was higher than 1.0 mg/ml. IAN significantly (P < 0.05) reduced the disease when it was foliar applied during the period from 3 days prior to inoculation to 1 day after inoculation. When IAN was applied in combination with a copper bactericide Kocide 3000, additive effect was observed in reducing both disease severity and bacterial growth, compared to either IAN or copper alone, for both copper-sensitive and copper-resistant X. perforans strains. Results from this study indicated that IAN significantly reduced bacterial leaf spot on tomato and enhanced the efficacy of copper against X. perforans. Specifically, IAN significantly improved the control of bacterial leaf spot caused by a copper-resistant X. perforans strain.

Integration of biological and conventional treatments in control of pepper bacterial spot

Bacterial spot caused by Xanthomonas euvesicatoria is one of the most devastating pepper diseases in Serbia. Questionable seed quality, climatic conditions, and frequent irrigation during summer favour the disease occurrence and spread. The available management practices do not provide adequate disease control. Therefore, development of alternative and more sustainable disease management strategies is needed. Integration of classical and biological treatments could be an effective, environmentally safe option for reducing pepper bacterial spot severity. In order to develop an efficient integrated disease management program, we studied efficacy of biocontrol agents (bacteriophage strain KФ1 and two strains of Bacillus subtilis AAac and QST 713), systemic acquired resistance (SAR) inducer (acibenzolar-S-methyl - ASM), a commercial microbial fertilizer (Slavol), copper based compounds (copper hydroxide and copper oxychloride) in combination with or without mancozeb, and antibiotics (streptomycin sulphate and kasugamycin). They were applied as single treatments in two separate field experiments. Based on the single treatment efficacy, various combinations of the treatments were chosen for further testing in three separate field experiments. Additionally, we evaluated potential negative effect of ASM on pepper growth and yield in the growth chamber experiment. All the tested single treatments significantly reduced disease severity compared to the inoculated control (IC), except microbiological fertilizer and the antagonistic strain AAac. Integration of copper hydroxide, ASM and bacteriophages was the most efficient treatment, reducing the disease intensity by 96–98%. The results indicated that this combination may be an adequate alternative program for control of pepper bacterial spot.

Nano-Magnesium Oxide: A Novel Bactericide Against Copper-Tolerant Xanthomonas perforans Causing Tomato Bacterial Spot

Bacterial spot caused by Xanthomonas perforans causes significant damage on tomato in Florida. Due to the presence of copper (Cu)-tolerant X. perforans strains, Cu bactericides are not effective in disease management. Hence, there is a critical need to find alternatives for Cu. Antibacterial activity of magnesium oxide (Nano-MgO), and other metal oxide nanoparticles, were evaluated against a Cu-tolerant and -sensitive X. perforans strain. In vitro experiments demonstrated high antibacterial activity of Nano-MgO against both strains compared with the commercial Cu. The minimum inhibitory concentration of Nano-MgO is 25 µg/ml and the minimum bactericidal concentration is 100 µg/ml against a Cu-tolerant X. perforans strain after 4 h of exposure. Structural changes in the bacterial membrane following exposure to Nano-MgO treatments compared with the controls were observed using transmission electron microscopy. In two greenhouse experiments with a Cu-tolerant strain, bacterial spot severity was significantly reduced by Nano-MgO at 200 µg/ml compared with Cu-ethylene bis-dithiocarbamate (grower standard), and the untreated control (P = 0.05). In three field experiments, Nano-MgO at 200 µg/ml significantly reduced disease severity with no negative impact on yield compared with the untreated control. Inductively coupled plasma mass spectrometric analysis of the fruit confirmed that Nano-MgO application did not lead to the accumulation of Mg, Cu, Ca, K, Mn, P, and S. This study is the first to demonstrate the potential of Nano-MgO against bacterial spot of tomato.

Yellow passion fruit reaction to Xanthomonas axonopodis pv. passiflorae and to Cowpea aphid-borne mosaic virus

Yellow passion fruit (Passiflora edulis Sims) yield and longevity have been drastically reduced by bacterial spot (Xanthomonas axonopodis pv. passiflorae - Xap) and passion fruit woodiness disease (PWD) (Cowpea aphid-borne mosaic virus - CABMV). This study was aimed at evaluating the reaction of 11 genotypes of yellow passion fruit, based on the reaction of their progenies, to both mechanically inoculated Xap and CABMV, under greenhouse conditions. There was a progressive increase in bacterial spot and PWD severity with time. BRS Gigante Amarelo, MAR20#12, and MAR20#34 were selected as the progenies with lowest bacterial spot severity and disease progress over time. MAR20#2005, EC-L-7, UnB2015-1, and EC-3-0 presented the lowest PWD severity and disease progress over time. These progenies, along with individual plants from other progenies in which disease severity was significantly low until the last evaluation, will be cloned and tested again for Xap and CABMV, including other isolates.

Effect of environmental factors on diseases of betelvine (Piper betle) in Assam

The cultivation of betelvine is hindered by a number of fungal and bacterial diseases resulting in heavy loss in leaf yield every year. Environmental factors play an important role on growth, dissemination and infection of pathogen as well as influence the expression of susceptibility/resistance of the host plant after infection. Therefore, an experiment was undertaken to study the influence of temperature, humidity and rainfall on the development of the diseases of betelvine under Jorhat conditions. The intensity of major diseases of betelvine viz anthracnose leaf spot caused by Colletotrichum capsici (Syd.) Butler and Bisby, and bacterial leaf spot caused by Xanthomonas axonopodis pv. betlicola (Vauterin et al. in Int J Syst Bacteriol 45:472–489, 1995) aggravated during rainy season. Percent Disease Index (PDI) of anthracnose leaf spot increased from 0% in November–March to 30.1% in July. PDI of bacterial leaf spot (30.6%) reached its peak during the months of August–September. Anthracnose did not appear during the months from November to April. However, PDI of bacterial leaf spot gradually decreased from September to 0% in March. Relationship between disease severity of anthracnose leaf spot and the meteorological parameters (maximum and minimum temperature, evening relative humidity and rainfall) was strong and positive. A moderate positive linear relationship was observed between disease severity of bacterial leaf spot and the meteorological parameters such as maximum temperature and evening relative humidity. However, strong positive linear relationship was observed with minimum temperature and rainfall.