Phaseoli Var Research Articles

Heavy metal resistance and bioremediation capacity of rhizospheric strain BioRPaz-3 Pseudomonas azotoformans endowed with antifungal activities and multi-abiotic stress tolerance in in vitro trials

This study is designed to characterize the importance of heavy metal resistance and bioremediation capacity using Gram-negative bacteria Pseudomonas azotoformans under various abiotic stresses. Results obtained showed that the bacterial strains were significantly resistant to pH (4, 6, 7, 8, and 10). Most of them were also tolerant to drought (0.4 Mpa-2.4 Mpa), temperature (20 °C, 30 °C, 40 °C, and 45 °C), and salinity (200–600 mM). All the strains were resistant against lead (Pb) concentrations (100 µg/ml, 200 µg/ml, and 500 µg/ml) and copper (Cu) concentrations (200 µg/ml, 500 µg/ml, and 1000 µg/ml). Two Pseudomonas azotoformans strains (BioRParz-2 and BioRPaz-4) showed significant antibacterial activity against Xanthomonas axonopodis pv. phaseoli var. fuscans. Some bacterial strains expressed significant antifungal activities toward phytopathogenic fungi (Fusarium oxysporum f. sp. phaseoli and Stemphylium botryosum). The screening lead to the selection of the multi-abiotic stress-resistant strain BioRPaz-3 pH (6, 7, 8 and 10), temperature (20 °C, 30 °C, 40 °C and 45 °C), salinity up to (600 mM), drought up to (2.4 Mpa), Pb (100 µg/ml, 200 µg/ml, and 500 µg/ml), and Cu (200 µg/ml, 500 µg/ml, and 1000 µg/ml), and endowed with antifungal activities against Fusarium oxysporum f. sp. phaseoli (48.89% ± 1.92%) and Stemphylium botryosum (83.33% ± 2.22%). This strain can be used for Pb and Cu bioremediation

Phosphites of manganese and zinc potentiate the resistance of common bean against infection by Xanthomonas axonopodis pv. phaseoli

AbstractCommon bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli var. fuscans (Xapf), negatively impact common bean production globally. Considering the potential of phosphites to protect plants against different diseases, this study investigated the potential of using manganese (Mn) and zinc (Zn) phosphites in common bean for CBB control. Plants were inoculated with Xapf 48 hr after being sprayed with water (control) and solutions (7.5 ml/L) of Mn and Zn phosphites. The area under common bacterial blight progress curve (AUCBBPC) was significantly lower by 34% and 59% for Mn and Zn phosphite treatments in comparison with the control treatment. The AUCBBPC was significantly reduced by 38% for Zn phosphite‐sprayed plants compared to Mn phosphite treatment. Phosphite‐sprayed plants displayed higher values for area under the curves of net CO2 assimilation rate, stomatal conductance to water vapour, transpiration rate and internal‐to‐ambient CO2 concentration ratio than non‐sprayed plants. This indicates the effect of Mn and Zn phosphites in attenuating the photochemical dysfunctions caused by Xapf infection. Moreover, plants sprayed with Mn phosphite displayed higher values for area under the curves of efficiency in capturing the excitation energy of open reaction centres of PSII and electron transport rate than those non‐sprayed indicating their capacity to preserve the capture and the use of the collected energy more efficiently. Lower AUCBBPC for Zn phosphite‐sprayed plants resulted in higher concentrations of total chlorophylls. The Zn phosphite‐sprayed plants showed higher values for area under the curves of β‐1,3‐glucanase, phenylalanine ammonia‐lyase, polyphenoloxidase, ascorbate peroxidase and superoxide dismutase activities. The Zn phosphite spray primed the plants to enhance their defence response and antioxidant capacity to reduce Xapf‐triggered oxidative stress with the preservation of the photosynthetic apparatus more efficiently.

English

Cowpea production is common among smallholder subsistence farmers of Western Kenya due to its wide ecological adaptation. However, this crop is affected by cowpea rust Uromyces phaseoli var vignae (Baarel) Arth disease, causing economic yield losses with limited control measures. This study therefore, evaluated cowpea rust disease incidence (DI) and severity (DS) on growth of selected improved cowpea genotypes. A Randomized Complete Block Design (RCBD) in split plot arrangement experiment was conducted in Busia and Kakamega counties, Kenya during short rains of 2018 and long rains of 2019. Cowpea genotype: K80, KVU 27-1, Tumaini, Dakawa and local variety was the main factor and cropping system: pure stand cowpea and cowpea intercropped with maize was the sub plot-factor. Data were subjected to Mixed model ANOVA using SAS. The DI and DS were 41 and 39% respectively less in Dakawa and Tumaini with more cowpea leaf and grain yields compared to other genotypes. On the other hand, DI and DS were 35 and 56% respectively less in pure stand cowpea compared to intercrop cowpea. Pure stand cowpea also had more leaf and grain yields. The results indicate that Dakawa and Tumaini cowpea genotypes have potential resistance to cowpea rust and the conditions could be improved by planting cowpea in pure stand. Key words: Cowpea genotype, cropping system, cowpea rust incidence, severity. &nbsp

Effect of Rust (Uromyces Phaseoli Var. Vignae) Infection on Photosynthetic Efficiency, Growth and Yield Potentials of Cowpea (Vigna Unguiculata L. Walp) in an Open Field System

Cowpea rust fungus affects photosynthetic rate and physiological performance of the host plant through the induction of structural changes in the host cell. The study assessed the effects of rust fungus onnet photosynthetic efficiency and yield performance of cowpea genotypes under field conditions. The experiment was conducted in the minor cropping season following a randomized complete block design outlay with three replications. Chlorophyll fluorescence of healthy leaves and rust-infected leaves of each cowpea genotype was determined by a non-destructive method.Rust disease severities of the infected leaves were assessed based ona diagrammatic scale. The effect of rust on the net photosynthetic rate was quantified by the model Px / Po = (1 – x)β. Growth and yieldtraits of the cowpea genotypes and correlation between seed yield and photosynthetic efficiency were determined. The cowpea genotypes responded differently to rust infection as expressed in net photosynthetic rates,growth, and yield. The pathogen impaired photosynthetic efficiency of leaf tissue beyond the observed diseased leaf area. Seed yield was more closely related to the βestimate than that observed for the relative net photosynthetic rate.

THE POTENTIAL APPLICATION OF Origanum dubium Boiss. ESSENTIAL OIL AS A SEED PROTECTANT AGAINST BEAN AND TOMATO SEED-BORNE BACTERIAL PATHOGENS

Origanum dubium is a valuable wild oregano species of the natural flora of Antalya, Turkey. In this study, we extracted essential oil (EO) by hydro-distillation of the aerial parts of selected O. dubium chemotype with highest EO content, and analyzed by gas chromatography/mass spectrometry. Carvacrol was the pri- mary component (85.9%) among 24 different compounds in the EO. The volatile test showed minimum inhibitory effect of the EO against Xanthomonas axonopodis pv. vesicatoria, Clavibacter michiganen- sis subsp. michiganensis, Xanthomonas axonopodis pv. phaseoli, Xanthomonas axonopodis pv. phaseoli var. fuscans, and Pseudomonas syringae pv. tomato, at 309, 303, 318, 254, and 901 µL/mL, respectively. A 1-hour treatment of bean and tomato seeds in the volatile phase of the EO effectively sterilized the seeds from bacterial pathogens without inhibiting their germination. To the best of our knowledge, this is the first study on the potential for the use of O. dubium EO as a seed protectant against bean and tomato seed-borne bacterial pathogens.

Marker-assisted Pyramiding Resistance Genes Against Angular Leaf Spot and Common Bacterial Blight Disease into Preferred Common Bean Cultivar

Angular leaf spot (ALS) caused by Pseudocercospora griseola and common bacterial blight (CBB) caused by Xanthomonas campestris pv phaseoli X. campestris pv. phaseoli var. fuscans are the most economically important diseases of common bean production in Ethiopia. This research aims at pyramiding the Phg-2 R gene for angular leaf spot resistance and two CBB major resistance quantitative trait loci (RQTLs) into the background of the most popular and susceptible common bean cultivar “REDWOLAITA” (RW) with the aid of marker-assisted breeding method. Marker-assisted Parallel Back Crossing (MAPBC) breeding scheme with three separate parallel backcrossing streams were adopted for tracking three independent resistance loci linked to g796 ( Phg-2 for ALS resistance) and, SU91 and SAP6 genetic markers from two different donor parents to the REDWOLAITA recurrent parent. The two donor parental lines VAX6 (with known RQTLs tagged by the SAP6 and SU91 genetic markers on linkage groups 10 and 8, respectively) and MEX54 with the Phg-2 R gene tagged by the g796 genetic marker at the linkage group 8 were used in the gene pyramiding program. After the BC4 generation, progenies that combined SAP6 and g796 genetic markers were created and selected from the BC4 inter-crossing of progenies. Then, further inter-crossing was made between selected progenies that combined the SAP6 and g796 genetic markers with selected progenies with the SU91 genetic marker. Finally, from this study we developed Monogenic Near Isogenic Lines (MNILs) with R genes tagged by the SAP6, g796, and SU91 molecular markers and polygenic PNILs with different gene combination includes MNIL SAP6 , MNIL SU91 & MNIL g796 , polygenetic PNILs SAP6/g796 , PNILs SU91/g796 , PNILs SAP6/SU , PNILs SAP6/g796/SAP6 , with more than 97% genome recovered from the RW genetic background. Marker-assisted backcrossing facilitated selection of progenies that combined good agronomic traits with resistance loci were constructed from the RW common bean cultivar genetic background and tested under the screening house condition. The developed lines showed high level of disease resistance to the strains of CBB and ALS present under the screening conditions. They were selected to be multiplied and tested under multiple environment, before varietal release and wider production. Developed MNILs with good agronomic background will also be used as alternative donor parent for the future gene pyramiding program.

Identification of common bean genotypes with dual leaf and pod resistance to common bacterial blight disease in Uganda

Common Bacterial Blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Xap) and Xanthomonas axonopodis pv. phaseoli var. fuscans (Xapf), is a serious disease that affects common bean production worldwide. In Uganda, it is the most severe and widely occurring bacterial disease, causing significant yield losses in common bean. Although various sources of resistance have been developed around the world, none of the varieties grown in Uganda is known to be resistant. The objective of this study was to identify lines with combined leaf and pod resistance for introgression into locally adapted but susceptible Ugandan genotypes. A total of 132 common bean accessions was evaluated in a screenhouse and under field conditions, in an 11x12 alpha lattice design. Genotypes were inoculated with a local isolate in a screenhouse; while the plants were left to undergo natural infestation in field. Results indicated significant differences (P<0.001) in genotypic reactions against the CBB disease, with a range of disease scores of 2.2 - 7.8 on leaves and 2.6 - 7.1 on pods (1-9 CIAT disease scale), suggesting high genetic variability among the tested germplasm. Relatively low correlation (r = 0.39) was observed between leaf and pod reactions, suggesting differential expression of CBB resistance in these two plant organs. Overall, four genotypes, NE2-14-8, NE17-14-29, NE14-09-78 and VAX3, consistently showed resistance in both screenhouse and field evaluations, leaf and pod inoculations and at all sampling stages. These genotypes were, therefore, identified for transferring CBB resistance into Ugandan susceptible market class bean varieties. Key words: CBB, Phaseolus vulgaris , Xanthomonas axonopodis

Analysis of the Molecular Diversity of Common Bacterial Blight (Xanthomonas campestris pv. phaseoli and X. campestris pv. phaseoli var. fuscansi) Strains from Ethiopia Revealed by Rep-PCR Genomic Fingerprinting

Common bacterial blight (CBB) disease of the common bean (Phaseolus vulgaris) caused by Xanthomonas campestris pv. phaseoli and X. campestris pv. phaseoli var. fuscans, is one of the most damaging foliar diseases of common bean production in Ethiopia. CBB causes economic losses due to reduction in seed quality and yield in common bean producing regions of Ethiopia. Currently, information on the genetic diversity of CBB strains in Ethiopia has been lacking. Here, for this specific study common bean bacterial blight strains were obtained from infected leaves collected from diverse bean growing areas. The collected strains of CBB were characterized to study the genetic diversity and relatedness of the CBB strains using repetitive extragenic elements polymerase chain reaction (rep-PCR) genomic fingerprinting technique. Analysis of Molecular Variance (AMOVA) revealed the existence of genetic diversity among bacterial strains and confirmed the presence of genetically distinct strains in Ethiopia. CBB pathogens are seed-borne so the lack of geographic differentiation among the six-different common bean growing localities could be the result of the distribution of one or some limited bacterial genotypes. Common bean improvement programs that develop CBB-resistant bean varieties for higher production should consider this information to determine the relevance and extent of resistance of improved bean cultivars.

Effects of Temperature and Moisture on Growth of Common Bean and Its Resistance Reaction against Common Bacterial Blight (Xanthomonas axonopodis pv. phaseoli strains)

Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli Smith (Xap) and Xanthomonas axonopodis pv. phaseoli var. fuscan Burkholder (Xapf) is the most serious biotic constraint of common bean (Phaseolus vulgaris L.) production. Variables temperature and moisture are dominant climate factors that affect common bean growth as well as the development of CBB epidemics. Two sets of experiments were conducted in the Plant Pathology Laboratory of Haramaya University) to assess the effect of temperature and moisture on the resistance level of common bean in 2014 and 2015. In the first experiment, two common bean varieties (Gofta and Mexican 142) were inoculated with two bacterial strains (Xap and Xapf) and a control were incubated at four temperature levels (28°C, 30°C, 32°C and 34°C) in growth chambers. In the second experiment, three-soil moisture levels (100%, 75% and 50%) were employed to that of experiment one. The treatment combinations were arranged in factorial completely randomized design (CRD) in the growth chambers for both series of experiments. The disease rating was significantly (P

Occurrence and Importance of Xanthomonas axonopodis pv. Phaseoli in Common Bean (Phaseolus vulgaris L) Seed Produced under Different Seed Production System in Central Rift Valley of Ethiopia

Common bacterial blight of bean caused by the seed-borne bacteria Xanthomonas axonopodis pv. phaseoli (Xap) (Smith) Vauterin and X. axonopodis pv. phaseoli var. fuscans (Burkholder) Starr and Burkholder is one of the most constraint of common bean production all over the world. The pathogen is seed-borne and survives as long as the seed remains viable. Use of pathogen-free seeds has been the main method used to control the disease in most bean production areas, and detection of this pathogen in seeds is essential for effective disease control. This study was carried out to detect and characterize Xap in seed lots collected from different seed dealers and local markets in Central Rift Valley of Ethiopia. A semi-selective medium Xanthomonas campestris pv. phaseoli (XCP1) and yeast extract-dextrose-calcium carbonate agar (YDCA) were used to recover the bacterium from whole bean seed extract and direct seed plating respectively. The pathogenicity test was done on Mexcan-142 bean cultivar to confirm pathogen identification. Colonies of the bacterium were yellow, mucoid and convex on XCP1 media and zone of hydrolysis formed around them. Further biochemical test results also confirm that the colonies were gram negative, rod shape and hydrolyze starch, casein and Tween80. The results confirmed the presence of seed borne Xap in all seed dealers and local market seed lots in the study area. The result reveled Xap was prevalent in 79.27% of the total seed samples collected. Lower prevalence (21.43%), seed infection percentage (1.643%) and bacterial population were resulted in seed lots from Melkassa Agricultural Research Center seed lots; while the higher prevalence, seed infection percentage and bacterial population were observed in cooperative union, local market, and seed producer’s cooperative seed lots. From the result, it can be concluded that Xap was potentially recovered from naturally infected seeds using XCP1 media and the pathogen is highly distributed in seed lots in the study area with high prevalence in farmer’s produced seed lots. Therefore, seed plating on semi selective medium XCP1 can be used as standard method for routine analysis of Xap from bean seeds. Seed dealers in the study area should follow strict disease free seed production programs and farmers in the study area should be encouraged not to use local market and/or their own saved seeds for planting purpose.

Evaluation of seedborne bacterial pathogens on common bean cultivars grown in central Anatolia region, Turkey

Bacterial diseases of bean cause economically important losses worldwide. The most important method for managing bacterial diseases on bean is the use of pathogen-free seed. In this study, 198 different dry bean seed samples of six different cultivars including Dermason, Cali, Sira, Battal, Bombay and Seker, were collected from 12 provinces of Central Anatolia Region of Turkey. All were tested to investigate the seedlots as primary inoculum sources of the major bacterial diseases. The data revealed that 22,72 %, 13,63 %, 11,11 %, 1,51 % and 0.5 % of seed samples tested were contaminated with five seedborne bacterial pathogens, Pseudomonas savastanoi pv. phaseolicola (Psp), Pseudomonas syringae pv. syringae (Pss), Xanthomonas axonopodis pv. phaseoli (Xap), X. axonopodis pv. phaseoli var. fuscans (Xapf) and Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), respectively. All bacterial strains isolated were identified based on morphological, physiological, biochemical, molecular and pathogenicity tests. The results showed that Psp and Pss were found together on cv. Cali; Psp and Xap on cv. Dermason and cv. Sira; and Pss and Xap on cv. Seker, cv. Dermason, and cv. Cali. Therefore, the results in the present study suggested that evaluation and selection of pathogen-free seeds are very important for preventing the spread of pathogens and effective management of seed borne bacterial diseases prevalent in bean growing regions; in addition to implementation of integrated crop production strategies such as crop rotation, sanitation, seed treatment, tolerant/resistant cultivar selection and proper bactericide application.

Caracterización morfológica y molecular de una colección de aislamientos de Phomopsis longicolla (teleomorfo desconocido: Diaporthales) de la región templada y subtropical de Argentina

Diaporthe (teleomorpho)-Phomopsis - (anamorph) (DP) is a fungal group of great genetic diversity with over 900 species associated to a wide host range that includes cultivated and uncultivated species, forest, fruit trees and weeds. DP isolates are hemibiotrophs and have different sources of primary inoculum as stubble and seeds to restart cycles of parasitism - saprophytism. They colonize host tissues from early plant stages and establish different nutritional relationships, acting as endophytic and necrotrophic fungi. The plasticity of the Phomopsis genus has favored its expansion to different agro-ecosystems and various hosts constituting an epidemiological risk. The objective was to validate the identity and evaluate the biological relationships among 12 isolates of P longicolla and D. phaseolorum var. sojae (anamorph P phaseoli var. sojae) obtained in different tempered and subtropical agro-environments of Argentina, in order to analyze the variability and strategies for preserving fungal biodiversity. Macromorphological attributes (such as texture and color of colonies, stroma shape and distribution, pycnidia and perythecia shape and distribution) and micro-morphological characteristics (such as size and shape of conidia, asci and ascospores) allowed identifying three new isolates as P longicolla. A complementary molecular analysis was also made to overcome the limitations derived from the morphological analysis, thus the AFP.8413 isolate was finally identified as P longicolla. The molecular characterization was useful to identify the evaluated isolates and to group them in four taxa of the Diaporthe-Phomopsis complex: ten isolates were included in P. longicolla, one isolate was included in D. phaseolorum var. sojae (anamorph P. phaseoli var. sojae), one isolate was identified as D. phaseolorum var. caulivora and two isolates were included in D. phaseolorum var. meridionalis. The use of phenotipic and molecular tools have contributed to an accurate identification of P longicolla, and comprehension about the biological relationships (homo or heterothallic hibridizations) among D. phaseolorum varieties (P phaseoli) and species of Diaporthe-Phomopsis. This allowed also a better understanding of the mechanisms of fungic plasticity, to colonize and expand their host range and genetic variability, promoting thus their biodiversity conservation. Rev. Biol. Trop. 63 (3): 871-884. Epub 2015 September 01.

Detection and quantification of Xanthomonas axonopodis pv. phaseoli and its variant fuscans in common bean seeds

The common bacterial blight of common beans (CBCF), a disease caused by Xanthomonas axonopodis pv. phaseoli (Xap) and Xanthomonas axonopodis pv. phaseoli var. fuscans (Xapf), significantly reduces grain yield and seed quality. Because this bacterium is mainly disseminated through infected seeds, efficient detection of Xap and Xapf is important to assure the productivity and quality of the crop. In this study, various techniques that included different extraction techniques (two different incubation times, with and without centrifugation) and five culture media (Kado 523, GYCA, MXP, NSA, and PTSA) were tested for the detection of the seed-borne inoculum, using three different seed samples. Overnight incubation of the seeds, followed by centrifugation and incubation in Kado 523 resulted in higher extraction of Xap and Xapf. The best extraction technique was overnight incubation followed by centrifugation, and the best medium was PTSA. Among the tested culture media, PTSA provided better identification and counting of the bacterial colonies, thus allowing the quantification of the seed infection levels.

Direct and Marker‐Assisted Selection for Resistance to Common Bacterial Blight in Common Bean

ABSTRACTCommon bacterial blight (CBB) caused by Xanthomonas campestris pv. phaseoli and X. campestris pv. phaseoli var. fuscans is a seed‐borne disease that can significantly reduce yield and seed quality of common bean (Phaseolus vulgaris L.). Disease resistance is the most effective management strategy, but most common bean cultivars have no CBB resistance. Marker‐assisted selection (MAS) shows promise as a method to facilitate pyramiding CBB resistance between common bean gene pools. This study compared the efficiency of direct disease resistance selection (DDS) and MAS for the pyramiding and transfer of CBB resistance into dark red kidney bean. Direct disease resistance selection and MAS were applied independently, from the F1 through the F5, in an inter‐gene pool double‐cross population, Wilkinson 2/dark red kidney (DRK) 2//DRK 1/VAX 3. Replicated trials were performed in the greenhouse and field in 2006 and 2007 to assess levels of CBB resistance in 15 breeding lines independently developed with each method. Under high disease pressure, in two greenhouse environments, 12 resistant breeding lines were obtained with DDS compared with six using MAS, and the overall CBB mean disease severity index was 3.3 for DDS and 4.2 for MAS. Under moderate disease pressure in the field, there was no significant difference (p &gt; 0.05) between the responses of breeding lines developed by the two selection methods. The cost of DDS was US$1.55 per plant compared to $2.03 for MAS.

Transmission of plant-pathogenic bacteria by nonhost seeds without induction of an associated defense reaction at emergence.

An understanding of the mechanisms involved in the different steps of bacterial disease epidemiology is essential to develop new control strategies. Seeds are the passive carriers of a diversified microbial cohort likely to affect seedling physiology. Among seed-borne plant-pathogenic bacteria, seed carriage in compatible situations is well evidenced. The aims of our work are to determine the efficiency of pathogen transmission to seeds of a nonhost plant and to evaluate bacterial and plant behaviors at emergence. Bacterial transmission from flowers to seeds and from seeds to seedlings was measured for Xanthomonas campestris pv. campestris in incompatible interactions with bean. Transmissions from seeds to seedlings were compared for X. campestris pv. campestris, for Xanthomonas citri pv. phaseoli var. fuscans in compatible interactions with bean, and for Escherichia coli, a human pathogen, in null interactions with bean. The induction of defense responses was monitored by using reverse transcription and quantitative PCR (RT-qPCR) of genes representing the main signaling pathways and assaying defense-related enzymatic activities. Flower inoculations resulted in a high level of bean seed contamination by X. campestris pv. campestris, which transmitted efficiently to seedlings. Whatever the type of interaction tested, dynamics of bacterial population sizes were similar on seedlings, and no defense responses were induced evidencing bacterial colonization of seedlings without any associated defense response induction. Bacteria associated with the spermosphere multiply in this rich environment, suggesting that the colonization of seedlings relies mostly on commensalism. The transmission of plant-pathogenic bacteria to and by nonhost seeds suggests a probable role of seeds of nonhost plants as an inoculum source.

Antibacterial Activity of Essential Oil Components and Their Potential Use in Seed Disinfection

Among the main (> or = 0.7%) components of some essential oils, considerable antibacterial activity was shown by terpenoid and phenylpropanoid derivatives containing phenol and alcohol functionalities. A reduced or no activity was shown by those derivatives containing ketones, aldehydes, ethers, and ester functionalities as well as the remaining terpenoids. Eugenol emulsion treatments (1-8 mg/mL) of bean seeds bearing about 2.6 x 10(6) cfu/seed of strain ICMP239 of Xanthomonas campestris pv. phaseoli var. fuscans determined a highly significant reduction of the bacteria on seeds. In particular, eugenol at 4 mg/mL disinfect seeds bearing about 7.0 x 10(2) cfu/seed and lower densities. However, after 72 h, incubation treatments with 2, 4, and 8 mg/mL of eugenol caused germination reduction of 3%, 7%, and 16%, respectively, which was significantly different from the controls. No effect on germination was observed with 1 mg/mL eugenol emulsion treatment. These data indicate eugenol as potentially useful for bean seed disinfection from X. campestris pv. phaseoli var. fuscans. Further studies on the effects on seed vitality and on formulation of essential oils are needed.

Survival of Xanthomonas axonopodis pv. phaseoli var. fuscans in common bean leaflets on soil.

The aim of this study was to evaluate the survival of a strain of Xanthomonas axonopodis pv. phaseoli var. fuscans (Xap), resistant to streptomycin sulphate, in common bean leaflets placed on the soil surface and buried at a depth of 10 and 15 cm. Four assays were carried out from November 1998 to December 2000 in Bandeirantes (Parana, Brazil). The leaflets were collected every 15 days, crushed and the dilution-plated on a semi-selective medium. Under mild temperatures and low rainfall, Xap survived for 65 to 180 days in the leaflets on the soil surface, and for 30 to 120 days in those incorporated in the soil, regardless of the depth. When higher rainfall and temperatures occurred, the survival was from 45 to 60 days in the leaflets on the soil surface and from 30 to 45 days in those buried 10 or 15 cm deep.

Severidade da mela da soja causada por Rhizoctonia solani AG-1 IA em função de doses de potássio

O fungo Rhizoctonia solani pertencente ao grupo de anastomose 1 IA (AG-1 IA) é um dos patógenos mais importantes afetando a cultura da soja no Brasil. Este fungo causa queima da folha e/ou mela em soja, para a qual medidas de manejo cultural são consideradas alternativas importantes para controle antes do estabelecimento da doença. Há evidências de que a adubação potássica diminui substancialmente a severidade dos sintomas de várias doenças da soja como a queima foliar (Cercospora kikuchii), a seca da haste e da vagem (Phomopsis phaseoli var. sojae) e o cancro da haste (Diaporthe phaseolorum f. sp. meridionalis). Apesar das evidências do efeito do potássio no controle de várias doenças da soja, não há informação na literatura sobre o efeito desse nutriente no controle da mela. A hipótese testada foi que a mela da soja pode ser controlada através de incrementos na adubação potássica. De maneira geral, concluiu-se que, sob condições de casa de vegetação, o incremento de K no solo não resultou no controle da mela da soja. É necessário, entretanto, confirmar esta observação conduzindo-se experimentos sob condições de campo, podendo-se incluir a avaliação do efeito da doença sob aspectos da produção.

Phenotypic and Genetic Diversity in Strains of Common Blight Bacteria (Xanthomonas campestrispv.phaseoliandX. campestrispv.phaseolivar.fuscans) in a Secondary Center of Diversity of the Common Bean Host Suggests Multiple Introduction Events

ABSTRACT Common bacterial blight (CBB) disease of the common bean (Phaseolus vulgaris) is caused by Xanthomonas campestris pv. phaseoli and the brown-pigmented variant X. campestris pv. phaseoli var. fuscans. CBB first was described in Castilla y León County, Spain, in 1940, and is now a major constraint on common bean production. In this secondary center of diversity of the common bean, large-seeded Andean cultivars predominate, although medium-seeded Middle American cultivars also are grown. Xanthomonad-like bacteria associated with CBB in Castilla y León were characterized on the basis of carbohydrate metabolism, brown pigment production, genetic analyses (repetitive-element polymerase chain reaction [rep-PCR] and random amplified polymorphic DNA [RAPD]) and pathogenicity on cultivars representing the two common bean gene pools (Andean and Middle American). X. campestris pv. phaseoli was more prevalent (80%) than X. campestris pv. phaseoli var. fuscans (20%). Patterns of carbohydrate metabolism of Spanish CBB bacteria were similar to those of known strains; and only X. campestris pv. phaseoli var. fuscans strains utilized mannitol as a sole carbon source. rep-PCR and RAPD analyses revealed relatively little genetic diversity among Spanish X. campestris pv. phaseoli strains, and these strains were placed together with New World strains into a large cluster. Similar to other New World strains, representative Spanish X. campestris pv. phaseoli strains were highly pathogenic on bean cultivars of both gene pools, showing no gene pool specialization such as that found in certain East African strains. Genetic analyses and pathogenicity tests confirmed and extended previous results, indicating that these East African strains represent distinct xanthomonads that independently evolved to be pathogenic on common bean. X. campestris pv. phaseoli var. fuscans strains were more closely related and genetically distinct from X. campestris pv. phaseoli strains. However, two distinct clusters of X. campestris pv. phaseoli var. fuscans strains were identified, one having the most New World strains and the other having the most African strains. Spanish strains were placed in both clusters, but all strains tested were highly pathogenic on bean cultivars of both gene pools. Together, our results are consistent with multiple introductions of CBB bacteria into Spain. These findings are discussed in terms of breeding for CBB resistance and the overall understanding of the genetic diversity and evolution of CBB bacteria.

Xanthomonas axonopodis pv. phaseoli와 X. axonopodis pv. phaseoli var. fuscans에 의한 팥의 세균성잎마름병

A bacterial disease of small red bean (Phaseolus angularis) was observed on field-grown plants in Suwon in year 2003. Leaf symptoms initially appeared as water-soaked spots that gradually enlarged, became flaccid and necrotic and were often bordered by a small zone of lemon yellow tissue. In the case of severe infection, dead leaves were defoliated. Pod symptoms consisted of the lesions that were generally circular, slightly sunken and dark reddish brown. Isolation made from diseased leaves on yeast extract dextrose calcium carbonate agar yielded nearly pure cultures of a yellow-pigmented bacterium typical of a xanthomonad. Three bacterial strains were purified and used for further tests. Pathogenicity of strains was confirmed on 3-week-old small red bean plants sprayed with bacterial suspensions containing of phosphate buffered saline. The representative Xanthomonas strains isolated from small red bean were compared with X. axonopodis pv. phaseoli and X. axonopodis pv. phaseoli var. fuscans type strains for fatty acid profiles, biochemical tests and metabolic fingerprints using Biolog GN2 microplate, showing that all outcomes were indistinguishable between our isolates and reference strains. Two of three strains produced a melanin-like brown pigment extracellularly on King`s medium B agar. These results suggest that this new small red bean disease observed in Suwon is bacterial fuscous blight caused by X. axonopodis pv. phaseoli and X. axonopodis pv. phaseoli var. fuscans.