Diversity and activity of biosurfactant-producing Pseudomonas in the rhizosphere of black pepper in Vietnam

Aims: Phytophthora capsici is a major pathogen of black pepper and zoospores play an important role in the infection process. Fluorescent pseudomonads that produce biosurfactants with zoosporicidal activities were isolated from the black pepper rhizosphere in Vietnam, and their genotypic diversity and potential to control Phy. capsici root rot was determined. Methods: Biosurfactant‐producing pseudomonads were genotypically and biochemically characterized by BOX‐polymerase chain reaction (PCR), 16S‐rDNA sequencing, reverse‐phase‐high‐performance liquid chromatography and liquid chromatography‐masss spectrometry analyses. Results: Biosurfactant‐producing fluorescent pseudomonads make up c. 1.3% of the culturable Pseudomonas population in the rhizosphere of black pepper. Although BOX‐PCR revealed substantial genotypic diversity, the isolates were shown to produce the same biosurfactants and were all identified as Pseudomonas putida. When applied to black pepper stem cuttings, several of the biosurfactant‐producing strains provided significant disease control. In absence of the disease, several of the bacterial strains promoted shoot and root growth of black pepper stem cuttings. Conclusions: Biosurfactant‐producing pseudomonads indigenous to the rhizosphere of black pepper plants are genotypically diverse and provide a novel resource for the control of Phy. capsici root rot and growth promotion of black pepper stem cuttings. Significance and Impact of the Study: The results of this study provide a strong basis for further development of supplementary strategies with antagonistic bacteria to control foot and root rot of black pepper and to promote plant growth.     

Greenhouse and field evaluations of potassium phosphonate: the control of Phytophthora foot rot of black pepper in Vietnam

Phytophthora foot rot of black pepper caused by Phytophthora capsici is a major disease of black pepper throughout production areas in Vietnam. The disease causes collar, foot and tap root rots and eventual death of the infected vine. Potassium phosphonate was evaluated for the control of this disease in greenhouse and field trials. In greenhouse trials three-month-old vines treated with phosphonate by soil drenching (10–20 g a.i./l) and then inoculated with P. capsici mycelium (2% v/v soil) had significantly less foot rot compared to vines grown in non-treated soil. In field trials mature vines were treated with phosphonate at 50–100 g a.i/pole soil drenching or 10 g a.i./l by root infusion. After 10 days root, stem and leaf specimens were removed for bioassay by inoculation with 5 ml of P. capsici zoospores suspension (10⁶–10⁸ spores/ml). Soil drenching with phosphonate inhibited the colonisation of pathogen on excised leaf, stem and root tissues, significantly more than phosphonate root infusion. Our study provides further evidence supporting the efficacy of potassium phosphonate in the management of black pepper foot rot caused by P. capsici. The excised leaf and stem bioassay used in this study is a rapid and useful technique for testing the efficacy of systemic fungicides in controlling this disease.     

Screen of safflower (Carthamus tinctorius L.) genotypes against Phytophthora drechsleri and Fusarium solani,the causal agents of root rot disease

Safflower (Carthamus tinctorius L.) plants were affected by a severe root rot disease caused by Phytophthora drechsleri and Fusarium solani in Isfahan province of Iran during 2005–2007. Disease incidence was more than 30% in severely infected fields. Twenty-one safflower genotypes, including six local cultivars and 15 internal pure lines were evaluated for their resistance to root rot disease in laboratory and greenhouse conditions. Safflower seedlings were evaluated for lesion length on infected roots in laboratory, as well percentage of live seedlings in greenhouse. The results indicated a high negative correlation between lesion length on roots and percentage of live seedlings. The most resistant and susceptible genotypes to P. drechsleri were identified as pure line Karaj row 12 (KW12) and cultivar Koseh with lesion lengths of 10.01 and 15.51?mm on roots and 45.60 and 18.00% live seedlings, respectively. The most resistant genotype to F. solani was identified as pure line KW11 with a lesion length of 9.31?mm on roots as well 62.80% live seedlings. The most susceptible genotypes were identified as cultivar Koseh and pure lines KW2 and KW3 with lesion lengths of 13.29, 12.72 and 12.13?mm on roots and 25.60, 28.40 and 28.40% live seedlings, respectively. The most resistant genotypes to both P. drechsleri and F. solani were identified as pure lines KW15 and KW9 with a 55.40% live seedlings. The most susceptible genotypes were cultivars Koseh, Goldasht and pure lines KW6, KW3 and KW2 with 35.40, 35.40, 35.40, 37.60 and 37.60% live seedlings in greenhouse, respectively.     

RAPD analysis of local bell pepper genotypes in relation with powdery mildew incidence and fruit yield: Managing disease by single chemical molecule

Abstract

A field study was conducted to investigate powdery mildew disease incidence and fruit yield of locally available bell pepper genotypes by Kharif 2004 and Rabi 2005. The study includes a single chemical molecule in managing the powdery mildew disease during both the seasons. Field studies include five chemical treatments (T₁ to T₅) plus one water spray control and an untreated control in five replications each. The result shows that out all treatments T₅ was best in controlling the powdery mildew disease in genotype Indra by 77.1 and 73.7% of disease decrease over control and 85.3 and 95.7% increase in yield over control respectively during Kharif and Rabi. The next best performing genotypes were Arka Basant and California Wonder in terms of less disease incidence and high yield. Further, the study was extended to relate the selected varieties for its genetic diversity using Random Amplified Polymorphic DNAs, with respect to the disease incidence and yield. The highest genetic dissimilarity of 49% was noticed between the genotypes Indra and Arka Gaurav having contrasting characters such as high and low fruit yield, respectively. The lowest genetic diversity of 21% was noticed between the genotypes Arka Mohini and California Wonder that were similar in most of the morphological characters, fruit yield and susceptibility to the powdery mildew disease. Based on the molecular data, a remarkable difference was exhibited by the commercially grown bell pepper genotypes.     

Reactions of six cultivars of rice (Oryza sativa L.) to three fungal diseases

Abstract

Fungal diseases are the most important threat for rice production in the world. Rice fields were visited and sampled from diseased bushes to identify fungal diseases in Kohgiluyeh and Boyer-Ahmad province, in the south-west of Iran. Fungi were isolated from diseased tissues by Agar-plate method, and purified by single-spore or hyphal-tip methods. They were identified by studying morphological characteristics. The virulence of isolated fungi was evaluated on six dominant rice cultivars, Champa of temperate region, Champa of subtropical region, Gerdeh, Shamim, Fajr and Tarom, under greenhouse conditions. The experiment was set up in a factorial experiment in completely randomized design with four replicates. The incidence of three fungal diseases: brown spot caused by Curvularia australiensis and Bipolaris cookei, foot rot caused by Fusarium globosum and Fusarium sambucinum, and black root rot caused by Exserohilum pedicellatum, was proven in this study. Although, all of the tested cultivars significantly showed different reaction to these fungi, but the cultivars Champa of subtropical region and Tarom were resistant to foot rot as well as the black root rot and the cultivar Gerdeh was resistant to brown spot disease.     

Genetic diversity of soft rot strains of Pectobacterium,isolated from different hosts,using ISSR marker

Pectobacteria are one of the most important groups of plant pathogenic bacteria and have been reported in many countries including Iran. Thirty-five Iranian strains of pectobacteria were isolated from potato, cabbage, sugar beet, pepper, carrot, onion, cucumber, turnip and tomato host plants cultivated in Fars province of Iran, in 2013. The genetic diversity among the strains was evaluated using ISSR marker. The tested strains were rod-shape, motile with peritrichous flagella, gram-negative, facultative anaerobes, oxidase-negative, catalase-positive, and were able to cause potato rot, while they could not induce hypersensitive reaction on tobacco leaves. Based on phenotypic criteria, the isolated strains were categorised into three groups. The strains of first, second and third groups were related to Pectobacterium carotovorum subsp. carotovorum, Pectobacterium betavascularum and Dickeya chrysanthemi, respectively. According to ISSR assay, the primers that used in this assay showed significant diversity among the strains and the specific primers GTGC4, GAGC4 and GTG5 confirmed the classification.     

Effect of oxathiapiprolin on asexual life stages of Phytophthora capsici and disease development on vegetables

Phytophthora blight caused by Phytophthora capsici is a serious disease in the production of peppers and other vegetables worldwide. Application of fungicides is an important component in developing effective disease management programmes. However, resistance in P. capsici populations to some commonly used fungicides has been documented. Identification of effective new fungicides with different mode of actions is highly desirable. This study was conducted to determine baseline sensitivity of P. capsici isolates to oxathiapiprolin, the first member of a new class of isoxazoline fungicides, and efficacy of this compound for reduction of Phytophthora blight on bell pepper. A collection of 126 P. capsici isolates were evaluated and all the isolates were sensitive to oxathiapiprolin. EC₅₀ values of oxathiapiprolin in inhibiting mycelial growth, sporangium formation and zoospore germination of 25 selected isolates averaged 0.001, 0.0003 and 0.54 µg mL^?1, respectively. It appeared that asexual life stages of P. capsici were more sensitive to oxathiapiprolin than other compounds used for control of oomycete pathogens. In field studies, oxathiapiprolin applied at different rates through drip irrigation tubes, or by soil drench plus foliar sprays, reduced Phytophthora blight and increased pepper yield significantly. This is the first report of the efficacy of oxathiapiprolin in suppression of P. capsici, which indicates that oxathiapiprolin is effective in inhibiting the pathogen and has the promise to be a viable option for managing Phytophthora blight in bell pepper production.     

Root characteristics of grafted peppers and their resistance to <Emphasis Type="Italic">Fusarium solani</Emphasis>

Root rot caused by Fusarium solani, is one of the most severe diseases in pepper (Capsicum annuum L.). Grafting has been attempted as an effective means to control the disease, but little is known about the disease resistance mechanism in grafted pepper. Therefore, we investigated the changes of biomass, cell structure, and the secondary metabolism in roots of control (non-grafted pepper) and grafted peppers using cvs. Weishi and Buyeding as rootstocks and the cv. Xinfeng 2 as a scion. After a manual inoculation, less F. solani invaded grafted pepper roots and consequently less serious injury to the root cell ultra-structure compared with the control was found. The roots of grafted pepper infected with F. solani exhibited greater biomass production and root activity than the roots of infected controls. Grafting led to an increased content of salicylic acid, benzoic acid, vanillin, lignin, and polyamines, as well as activities of phenylalanine ammonia lyase, polyphenoloxidase, and peroxidase. These results suggest that grafting improved the resistance of peppers to root rot.     

Development of a bioassay to assess resistance to Fusarium oxysporum (Schlecht.) in asparagus (Asparagus officinalis L.)

Fusarium oxysporum is one of the major pathogens causing root and crown rot in asparagus. Breeding of cultivars resistant to F. oxysporum would be the most efficient strategy for pathogen control. In this study, a bioassay was developed for screening seedling resistance. The non‐destructive bioassay comprises inoculation with a highly aggressive F. oxysporum isolate, incubation in a climate chamber and quantification of disease symptoms by a digital image analysing system and a PTA‐ELISA. This bioassay is simple to implement and demonstrated high reproducibility. Subsequently, it was used to determine the resistance behaviour of 16 asparagus genotypes to F. oxysporum. The asparagus cultivars revealed different levels of susceptibility, whereas the wild relative A. densiflorus was confirmed to be resistant.     

Clonality in South African isolates and evidence for a European origin of the root pathogen Thielaviopsis basicola

Thielaviopsis basicola is a soil-borne fungal pathogen with a wide host range and a cosmopolitan distribution. It causes disease on many agricultural crops, and in South Africa is the causal agent of black pod rot of groundnuts and black root rot on chicory. Knowledge of the population diversity of T. basicola could provide valuable information regarding management strategies, the possible movement, origin, and reproductive strategies of the fungus. The objective of this study was to determine the population diversity of T. basicola isolates from groundnuts and chicory in South Africa using co-dominant polymorphic markers. These markers were also used to compare isolates from South Africa with those from other hosts and geographic regions. Seven loci revealed nine alleles and two genotypes, one on groundnut and one on chicory, differing at only two loci. T. basicola isolates from eight different countries and ten different hosts revealed 17 genotypes across the seven loci with 39 different alleles. The lack of diversity for the two South African host-related populations of isolates suggests that T. basicola was introduced into South Africa. Some evidence is provided for a European origin of the pathogen, possibly linked to trade in root crops.     

Inducible Proteins in Citrus Rootstocks with Different Tolerance Towards the Root Rot Pathogen Phytophthora palmivora

Activities of defence‐related proteins (β‐1,3‐glucanases, chitinases and peroxidases) and concentrations of total soluble phenolics were measured in roots and leaves of non‐infected and infected plants to investigate the response of different citrus rootstock genotypes to the root rot pathogen Phytophthora palmivora Butler. Infection with the pathogen increased concentrations of total proteins, total phenolics and β‐1,3‐glucanase activity in roots of all genotypes, and increases were associated with the extent of root mass reductions and thus susceptibility of the plants. Root chitinase and root peroxidase levels were slightly reduced or unaltered upon infection. β‐1,3‐Glucanase activity was also elevated in leaves of infected plants, but increases did not differ between tolerant and susceptible rootstocks. Effects of root infection on leaves were typically the reverse of effects on roots for chitinase‐ and peroxidase levels and more pronounced in susceptible rootstock genotypes. Although differences in enzyme expression were observed between susceptible and tolerant citrus seedlings, effects were usually associated with disease progression, and not with resistance to P. palmivora. It is suggested that increased activities of the proteins and soluble phenolics studied are not implicated in the primary defence to Phytophthora root diseases, but may contribute to the inhibition of the pathogen during infection in tolerant citrus.     

Genetic Diversity of Thanatephorus cucumeris Infecting Tomato in Iran

The necrotrophic fungus Thanatephorus cucumeris (anamorph Rhizoctonia solani) is among the most important soil‐borne pathogens which causes tomato foot and root rot worldwide. We investigated virulence and genetic relationships among and within different taxonomic groups of R. solani from the tomato‐growing regions in the north‐east of Iran. Characterization of R. solani taxonomic groups revealed that, of 56 isolates, four were AG‐2‐1, 16 were AG‐3 PT, 21 were AG‐4 HG‐I and 15 were AG‐4 HG‐II. Because interprimer binding site (iPBS), which is based on amplification of retrotransposons, is known as novel and powerful DNA fingerprinting technology, we selected four iPBS primers, which can detect polymorphisms of tomato foot root and root rot pathogen, for investigating genotypic variability of the isolates. The iPBS analyses separated various taxonomic groups of R. solani and showed great diversity among the isolates, demonstrating that the R. solani isolates obtained from tomato were not a clonal population. Crop rotation strategies and geographic location seem to be important factors affecting genetic structure of the isolates. Pathogenicity tests on tomato cultivar ‘Mobil’ showed significant differences in the virulence of various isolates. The overall results indicated that isolates of AG‐3 and AG‐4 were more virulent than AG‐2‐1. There was no significant correlation between genetic diversity and virulence of the isolates. This is the first report of R. solani AG‐4 HG‐II, causing tomato foot and root rot. Also, our research is the first in assessment of genetic diversity in fungal populations using iPBS molecular markers.     

Response of Resistant and Susceptible Bell Pepper (Capsicum annuum) to a Southern California Meloidogyne incognita Population from a Commercial Bell Pepper Field

To determine the presence and level of root-knot nematode (Meloidogyne spp.) infestation in Southern California bell pepper (Capsicum annuum) fields, soil and root samples were collected in April and May 2012 and analyzed for the presence of root-knot nematodes. The earlier samples were virtually free of root-knot nematodes, but the later samples all contained, sometimes very high numbers, of root-knot nematodes. Nematodes were all identified as M. incognita. A nematode population from one of these fields was multiplied in a greenhouse and used as inoculum for two repeated pot experiments with three susceptible and two resistant bell pepper varieties. Fruit yields of the resistant peppers were not affected by the nematodes, whereas yields of two of the three susceptible pepper cultivars decreased as a result of nematode inoculation. Nematode-induced root galling and nematode multiplication was low but different between the two resistant cultivars. Root galling and nematode reproduction was much higher on the three susceptible cultivars. One of these susceptible cultivars exhibited tolerance, as yields were not affected by the nematodes, but nematode multiplication was high. It is concluded that M. incognita is common in Southern California bell pepper production, and that resistant cultivars may provide a useful tool in a nonchemical management strategy.     

Morphological and Molecular Identification of Phytophthora tropicalis as Causal Agent of Crown and Root Rot on Albizia julibrissin

Isolates of a Phytophthora sp. were obtained from soil and root baiting of declining Albizia julibrissin plants grown in soil in an Italian nursery. Identification was performed on the basis of morphological, pathological and molecular features. As main characteristics, isolates did not grow at 35°C, were poorly pathogenic when inoculated on bell pepper plants, and had the average sporangium pedicel length longer than 100, being similar to Phytophthora tropicalis. A comparative study of internal transcribed spacer, beta‐tubulin, translation elongation factor‐1 alpha and cytochrome c oxidase subunit II (CoxII) sequences supported the identification of the isolates as P. tropicalis. Comparison included all the European isolate sequences available in GenBank. Pathogenicity tests reproduced symptoms of root and crown browning and rotting and wilting as originally observed on nursery plants. Considering all the results, we identified P. tropicalis as the causal agent of A. julibrissin decline, crown and root rot. To our knowledge, this is the first report of this host–pathogen combination in Italy or elsewhere. P. tropicalis has to be considered a serious threat to agricultural and natural environment because it is highly polyphagous and easy to spread due to its caducous sporangia.     

Assessment of laboratory methods for evaluating cassava genotypes for resistance to root rot disease

Field evaluation of six cassava genotypes for resistance to root rot disease was compared with three rapid laboratory methods (whole root inoculation, root slice inoculation, and stem inoculation) for resistance screening. Both the field evaluation and the three laboratory methods separated the varieties into resistant and susceptible groups. Genotypes 30572 and 91/02324 were resistant while 92/0247, 92/0057 and TME-1 were susceptible. One genotype (30001) was not consistent in its reaction between field evaluation and laboratory assays. In the laboratory assays with three fungal pathogens, different pathogens varied in their levels of virulence on host genotypes. With the most virulent pathogen (Botryodiplodia theobromae), the majority of the genotypes reacted in the same way across trials with the root slice and whole root assays. Due to the good correlation between the whole root assay and the field results, we recommend this for the routine assessment of cassava resistance to root rot disease and for the analysis of virulence of pathogen isolates. However, because of the advantages in terms of economy of labour, space, time, quantity of root and inoculum required, the root slice assay could be used for the preliminary screening of large cassava accessions. The selected genotypes can then be further screened with the whole root inoculation method.     

Cross-pathogenicity of Rhizoctonia solani strains on pasture legumes in pasture-crop rotations

In Australia, in the past, pasture legumes were rotated mainly with cereals, but increasingly these rotations now involve pasture legumes with a wider range of crops, including legumes. This increasing frequency of the leguminous host in the rotation system may be associated with increased root rots in legumes in the current pasture-crop rotations. The primary aim of this study was to see whether the pathogenicity on pasture legumes of strains of Rhizoctonia solani sourced from lupins and cereals (common crops in rotation with pastures) is associated with increased incidence of root rots in pasture legumes in the disease conducive sandy soils of the Mediterranean regions of southern Australia. The second aim was to determine sources of resistance among newly introduced pasture legumes to R. solani strains originating from rotational crops as this would reduce the impact of disease in the pasture phase. Fifteen pasture legume genotypes were assessed for their resistance/susceptibility to five different zymogram groups (ZG) of the root rot pathogen R. solani under glasshouse conditions. Of the R. solani groups tested, ZG1–5 and ZG1–4 (both known to be pathogenic on cereals and legumes) overall, caused the most severe root disease across the genotypes tested, significantly more than ZG6 (known to be pathogenic on legumes), in turn significantly >ZG4 (known to be pathogenic on legumes) which in turn was >ZG11 (known to be pathogenic on legumes including tropical species). Overall, Ornithopus sativus Brot. cvs Cadiz and Margurita, Trifolium michelianum Savi. cvs Paradana and Frontier and T. purpureum Loisel. cv. Electro showed a significant level of resistance to root rot caused by R. solani ZG11 (root disease scores ≤1.2 on a 1–3 scale where 3 = maximum disease severity) while O. sativus cvs Cadiz and Erica showed a significant level of resistance to root rot caused by R. solani ZG4 (scores ≤1.2). O. compressus L. cvs Charano and Frontier, O. sativus cv. Erica, and T. purpureum cv. Electro showed some useful resistance to root rot caused by R. solani ZG6 (scores ≤1.8). This is the first time that cvs Cadiz, Electro, Frontier, Margurita and Paradana have been recognised for their levels of resistance to root rot caused by R. solani ZG11; and similarly for cvs Cadiz and Erica against ZG4; and for cvs Charano, Erica, and Electro against ZG6. These genotypes with resistance may also serve as useful sources of resistance in pasture legume breeding programs and also could potentially be exploited directly into areas where other rotation crops are affected by these R. solani strains. None of the tested genotypes showed useful resistance to R. solani ZG1–4 (scores ≥2.0) or ZG1–5 (scores ≥2.5). This study demonstrates the relative potential of the various R. solani ZG strains, and particularly ZG1–4, ZG1–5, ZG4 and ZG6 to attack legume pastures and pose a significant threat to non-pasture crop species susceptible to these strains grown in rotation with these pasture legumes. Significantly, the cross-pathogenicity of these strains could result in the continuous build-up of inoculum of these strains that may seriously affect the productivity eventually of legumes in all rotations. In particular, when choosing pasture legumes as rotation crops, caution needs to be exercised so that the cultivars deployed are those with the best resistance to the R. solani ZGs most likely to be prevalent at the location.     

<i>Streptomyces</i> PRIO41 as plant growth promoter of jalapeño pepper plants and as biocontrol agent of <i>Fusarium</i>

Chili pepper is one of the main crops of economic importance in Mexico, and Fusarium wilting is a disease that limits its production. In addition, the inappropriate use of agrochemicals in farming activities generate environmental and health problems. Therefore, in this study the effectiveness of Streptomyces sp PRIO41 was evaluated as a (1) biocontrol agent of Fusarium spp and (2) plant growth promoter bacteria. Assays of pathogenicity and virulence of Fusarium spp. in jalapeño pepper seeds, and interactions of these pathogens with Streptomyces PRIO41 were evaluated under two nutritional conditions. In the greenhouse, the effectiveness of Streptomyces sp. PRIO41 was determined as a (1) biocontrol of Fusarium, and (2) plant growth promoter of wilt of pepper plants. The results showed that all fungal isolates caused symptoms in pepper seeds and seedlings with different degrees of virulence. Interactions in vitro showed that Streptomyces showed the most effective range of virulence against Fusarium isolates in the poor medium (37.6%-100%), with fungicidal effects in some cases. In the greenhouse, Streptomyces PRIO41 reduced Fusarium wilting up to a 40%, and positively affected all vegetative growth parameters, particularly plant height, leaf area, root length, and leaf and root dry biomasses. This study showed the potential of Streptomyces PRIO41 as a biocontrol agent of Fusarium spp., and as a biofertilizer of pepper plants.     

Molecular characterization of pathogenic Fusarium species in cucurbit plants from Kermanshah province, Iran

Fusarium is one of the important phytopathogenic genera of microfungi causing serious losses on cucurbit plants in Kermanshah province, the largest area of cucurbits plantation in Iran. Therefore, the objectives in this study were to isolate and identify disease-causing Fusarium spp. from infected cucurbit plants, to ascertain their pathogenicity, and to determine their phylogenetic relationships. A total of 100 Fusarium isolates were obtained from diseased cucurbit plants collected from fields in different geographic regions in Kermanshah province, Iran. According to morphological characters, all isolates were identified as Fusarium oxysporum, Fusarium proliferatum, Fusarium equiseti, Fusarium semitectum and Fusarium solani. All isolates of the five Fusarium spp. were evaluated for their pathogenicity on healthy cucumber (Cucumis sativus) and honeydew melon (Cucumis melo) seedlings in the glasshouse. F. oxysporum caused damping-off in 20–35 days on both cucurbit seedlings tested. Typical stem rot symptoms were observed within 15 days after inoculation with F. solani on both seedlings. Based on the internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA) restriction fragment length polymorphism (RFLP) analysis, the five Fusarium species were divided into two major groups. In particular, isolates belonging to the F. solani species complex (FSSC) were separated into two RFLP types. Grouping among Fusarium strains derived from restriction analysis was in agreement with criteria used in morphological classification. Therefore, the PCR-ITS-RFLP method provides a simple and rapid procedure for the differentiation of Fusarium strains at species level. This is the first report on identification and pathogenicity of major plant pathogenic Fusarium spp. causing root and stem rot on cucurbits in Iran.     

Occurrence and Characterization of the Bacterial Spot Pathogen Xanthomonas euvesicatoria on Pepper in Iran

We report in this study for the first time the occurrence of bacterial spot of pepper in Iran and both phenotypic and genetic characterization of its causal agent, Xanthomonas euvesicatoria. Pepper plants grown in 15 of 30 surveyed private gardens and commercial fields were infected by the pathogen in Marand County, East Azerbaijan Province, north‐western Iran. The obtained strains of X. euvesicatoria had different amylolytic and pectolytic activities compared with those reported for this species elsewhere. Pathogenicity tests showed that strains isolated from diseased pepper are able to infect tomato, in addition to pepper. Host range of the pathogen was assessed on eight annual plant species including crops and weeds by measuring the population dynamics. The host range assessment showed that in addition to pepper and tomato, known hosts of X. euvesicatoria, the Iranian strains were able to colonize a number of new hosts such as nightshade and common bean. In contrast, none of them were able to build up their population on cowpea, eggplant, bindweed and zucchini. All X. euvesicatoria strains obtained in this study were sensitive to copper sulphate and streptomycin at concentrations higher than 20 and 50 mg/l, respectively. Phylogenetic analyses of the strains using the sequences of gyrB and hrpB genes confirmed their species as X. euvesicatoria. Given a direct commercial trade of fresh solanaceous vegetables between Iran and Turkey, it is hypothesized that the pathogen entered north‐western Iran from eastern parts of Turkey through infected plant materials. Finally, the role of prevention – based on the use of healthy planting materials and resistant and/or tolerant plant varieties – to contain the potential disease epidemics is discussed.