Copper-resistant Strains Research Articles

Evidence for Acquisition of Copper Resistance Genes from Different Sources in Citrus-Associated Xanthomonads

ABSTRACT We determined that multiple and independent introductions of copper resistance genes have taken place for strains of Xanthomonas citri subsp. citri from Argentina and strains of X. alfalfae subsp. citrumelonis from Florida. This study compared the partial nucleotide sequences of principal copper resistance genes copL, copA, and copB from X. citri subsp. citri and X. alfalfae subsp. citrumelonis to strains of other Xanthomonas spp. resistant to copper that were isolated from 12 different countries or territories. The survey confirmed that the copLAB gene cluster is present in many species of Xanthomonas from different parts of the world. Alignment of partial nucleotide sequences of copper resistance genes among the copper-resistant (Cu(R)) strains of Xanthomonas detected homology of ≥92, ≥96, and ≥91% for copL, copA, and copB, respectively. Grouping of strains based on branching patterns of phylogenetic trees was similar for copL and copA but differed for copB. When the three genes were concatenated and analyzed using various phylogenetic methods, it appeared that the plasmid had been horizontally transferred and various populations were mutating based on selection pressure unique to geographic regions. Although high homology of the genes among the strains indicated that the copper resistance in xanthomonads has a common origin, the slight differences in nucleotide sequences within groups of strains indicated that Cu(R) genes have been independently exchanged among species of Xanthomonas throughout the world.

Foliar-Applied Small Molecule that Suppresses Biofilm Formation and Enhances Control of Copper-Resistant Xanthomonas euvesicatoria on Pepper.

We report a small molecule additive, a member of the 2-aminoimidazole (2AI) group that is an analogue of the marine sponge natural product oroidin that suppresses resistance of Xanthomonas euvesicatoria to copper and decreases biofilm formation in an in vitro system. In laboratory experiments, 2AI combined with copper reduced both bacterial multiplication in broth and bacterial recovery on pepper leaf discs of a copper-resistant strain of X. euvesicatoria to a level close to that of a copper-sensitive strain. Compound 2AI used alone exhibited minimal bactericidal activity. In 3 years of field experiments, when combined with a copper-containing material, copper hydroxide (Kocide 3000), and other antibacterial materials, these spray mixtures resulted in decreased bacterial spot foliar disease and increased fruit yields using hybrid bell pepper (Capsicum annuum) cultivars and copper-resistant strains of X. euvesicatoria. This study demonstrates the concept for using small molecules as additives to antibacterial compounds at nonbactericidal concentrations under field conditions that, in the laboratory, were demonstrated to suppress bacterial biofilms and copper-resistant strains.

Isolation, Characterisation and Detection of Plasmids from Chromium and Copper Resistant Bacterial Strains of Textile Effluents

Isolation, Characterisation and Detection of Plasmids from Chromium and Copper Resistant Bacterial Strains of Textile Effluents

Copper resistance genes from different xanthomonads and citrus epiphytic bacteria confer resistance to Xanthomonas citri subsp. citri

Genetic exchange is considered to be an important process in the selective adaptation of microorganisms to shifting and challenging environmental conditions. As a consequence of the copious use of copper bactericides, many species of plant pathogenic bacteria, including Xanthomonas citri subsp. citri (Xcc), have developed resistance to copper. This study assesses whether copper resistant (CuR) strains of other Xanthomonas species and citrus epiphytic bacteria pose a risk for the development of copper resistance in Xcc. CuR epiphytic bacteria were isolated on MGY agar from citrus leaves collected in two citrus groves treated with copper bactericides in Florida. Horizontal gene transfer of copper resistance genes was investigated within different Xanthomonas species and from citrus epiphytic bacteria to Xanthomonas. CuR epiphytic bacteria from citrus were screened for the presence of copper resistance genes homologous to copL, copA and copB genes from Xcc and characterized regarding tolerance to copper. Copper resistance determinants from a citrus epiphytic strain of Stenotrophomonas maltophilia (Stm) were cloned and expressed in Xcc and other Xanthomonas strains. Copper resistance genes in Xcc were determined to be present on a large (~300 kb) conjugative plasmid. Cu resistance was transferred via conjugation from two copper resistant citrus strains, Xcc and X. alfalfae subsp. citrumelonis (Xac), and two tomato pathogens, X. euvesicatoria (Xe) and X. perforans (Xp), to Xcc. PCR analysis revealed that two CuR strains from citrus, an epiphytic Xanthomonas ssp. and a strain of Stm, harboured homologs of the copper resistance genes found in CuR Xcc. The introduction of copLAB gene cluster from Stm into different xanthomonads conferred copper resistance to sensitive strains of Xcc, Xac, Xe and Xp. Based on these results there is a low, but significant, likelihood of horizontal gene transfer of copper resistance genes from other xanthomonads or epiphytic bacteria to Xcc in nature.

Antimicrobial activity of different copper alloy surfaces against copper resistant and sensitive Salmonella enterica

Copper has shown antibacterial effects against foodborne pathogens. The objective of this study was to evaluate the antibacterial activity of copper surfaces on copper resistant and sensitive strains of Salmonella enterica. Six different copper alloy coupons (60–99.9% copper) were tested along with stainless steel as the control. The coupons were surface inoculated with either S. Enteritidis or one of the 3 copper resistant strains, S. Typhimurium S9, S19 and S20; stored under various incubation conditions at room temperature; and sampled at various times up to 2 h. The results showed that under dry incubation conditions, Salmonella only survived 10–15 min on high copper content alloys. Salmonella on low copper content alloys showed 3–4 log reductions. Under moist incubation conditions, no survivors were detected after 30 min–2 h on high copper content alloys, while the cell counts decreased 2–4 logs on low copper content coupons. Although the copper resistant strains survived better than S. Enteritidis, they were either completely inactivated or survival was decreased. Copper coupons showed better antimicrobial efficacy in the absence of organic compounds. These results clearly show the antibacterial effects of copper and its potential as an alternative to stainless steel for selected food contact surfaces.

Monitoring for resistant populations of Xanthomonas citri subsp. citri and epiphytic bacteria on citrus trees treated with copper or streptomycin using a new semi-selective medium

Streptomycin has been tested as an alternative to copper bactericides, which are routinely used for the control of citrus canker (Xanthomonas citri subsp. citri, Xcc) in citrus producing areas where the disease is endemic. A major concern is that excessive use of copper as a bactericide may lead to development of copper-resistant strains of Xcc. In this study, we developed a semi-selective medium to recover copper or streptomycin-resistant strains of Xcc from citrus leaves. The newly developed semi-selective medium was used to monitor the effect of a 21-day-interval copper or streptomycin spray program on Xcc for three consecutive seasons and on citrus epiphytic bacterial populations for two seasons in a commercial grapefruit grove. Although, no copper- or streptomycin-resistant strains of Xcc were isolated after three seasons, we observed a significant increase over time in the frequency of citrus epiphytic bacteria resistant to these chemicals. Overall, the proportion of epiphytic bacteria resistant to streptomycin on treated and untreated leaves was proportionally lower than the copper-resistant bacterial population. When application of each bactericide was suspended for the season, the proportion of bactericide-resistant bacteria in the epiphytic population decreased to that of the non-treated bacterial population. Availability of an alternative bactericide, such as streptomycin, to integrate into a copper-based program would reduce the amount of each bactericide sprayed in citrus orchards and possibly lower the selection pressure for bacterial resistance to these chemicals.

Molecular Characterization of Copper Resistance Genes from Xanthomonas citri subsp. citri and Xanthomonas alfalfae subsp. citrumelonis

Copper sprays have been widely used for control of endemic citrus canker caused by Xanthomonas citri subsp. citri in citrus-growing areas for more than 2 decades. Xanthomonas alfalfae subsp. citrumelonis populations were also exposed to frequent sprays of copper for several years as a protective measure against citrus bacterial spot (CBS) in Florida citrus nurseries. Long-term use of these bactericides has led to the development of copper-resistant (Cu(r)) strains in both X. citri subsp. citri and X. alfalfae subsp. citrumelonis, resulting in a reduction of disease control. The objectives of this study were to characterize for the first time the genetics of copper resistance in X. citri subsp. citri and X. alfalfae subsp. citrumelonis and to compare these organisms to other Cu(r) bacteria. Copper resistance determinants from X. citri subsp. citri strain A44(pXccCu2) from Argentina and X. alfalfae subsp. citrumelonis strain 1381(pXacCu2) from Florida were cloned and sequenced. Open reading frames (ORFs) related to the genes copL, copA, copB, copM, copG, copC, copD, and copF were identified in X. citri subsp. citri A44. The same ORFs, except copC and copD, were also present in X. alfalfae subsp. citrumelonis 1381. Transposon mutagenesis of the cloned copper resistance determinants in pXccCu2 revealed that copper resistance in X. citri subsp. citri strain A44 is mostly due to copL, copA, and copB, which are the genes in the cloned cluster with the highest nucleotide homology (≥ 92%) among different Cu(r) bacteria.

Differential gene expression in response to copper in Acidithiobacillus ferrooxidans strains possessing dissimilar copper resistance

Locus afe_0454 from Acidithiobacillus ferrooxidans (At.ferrooxidans) is annotated as related to copper resistance in The Institute for Genomic Research database. In our study, two At.ferrooxidans strains, 26(#) and DC, with different levels of copper ion resistance were isolated from acid mine drainages at two major copper mines in China, and their copper-resistance capacity was determined. The 26(#) strain had a copper-tolerance level of 0.22 mol/L, whereas the DC strain had a lower copper-tolerance level of 0.04 mol/L. The mutant 26(#) was generated from strain 26(#), and its copper-tolerance level was 0.25 mol/L. Using real-time quantitative reverse transcription polymerase chain reaction, differential expression of the afe_0454 gene during copper ion stress of these three strains was investigated. The results showed that the expression of afe_0454 was increased under copper ion stress, indicating that the afe_0454 gene is sensitive to copper levels. Furthermore, the afe_0454 gene expression ratio varied in the different copper-resistant strains. Gene expression was highest in the highest copper-resistant strain. The deduced amino acid sequence of the afe_0454 gene was 56.87% non-polar, indicating the AFE_0454 protein was hydrophobic. Searching with the AFE_0454 protein in The Institute for Genomic Research database showed that the structure of the copper resistance protein D (CopD), which transports copper ions outside of the cell, had the highest sequence identity (46%). Bioinformatics analysis showed that the AFE_0454 protein has eight transmembrane helixes and was predicted to be localized to the plasma membrane. These results strongly suggested that the AFE_0454 protein is likely a transmembrane protein and might be directly involved in copper ion resistance.

Seasonal peculiarities of the epigenotype formation in the copper-sensitive and copper-resistant strains of Dunaliella viridis Teod. in the process of accumulative cultivation

Seasonal peculiarities of the epigenotype formation in the copper-sensitive and copper-resistant strains of Dunaliella viridis Teod. in the process of accumulative cultivation

Characterization of a unique chromosomal copper resistance gene cluster from Xanthomonas campestris pv. vesicatoria.

We characterized the copper resistance genes in strain XvP26 of Xanthomonas campestris pv. vesicatoria, which was originally isolated from a pepper plant in Taiwan. The copper resistance genes were localized to a 7,652-bp region which, based on pulsed-field gel electrophoresis and Southern hybridization, was determined to be located on the chromosome. These genes hybridized only weakly, as determined by Southern analysis, to other copper resistance genes in Xanthomonas and Pseudomonas strains. We identified five open reading frames (ORFs) whose products exhibited high levels of amino acid sequence identity to the products of previously reported copper genes. Mutations in ORF1, ORF3, and ORF4 removed copper resistance, whereas mutations in ORF5 resulted in an intermediate copper resistance phenotype and insertions in ORF2 had no effect on resistance conferred to a copper-sensitive recipient in transconjugant tests. Based on sequence analysis, ORF1 was determined to have high levels of identity with the CopR (66%) and PcoR (63%) genes in Pseudomonas syringae pv. tomato and Escherichia coli, respectively. ORF2 and ORF5 had high levels of identity with the PcoS gene in E. coli and the gene encoding a putative copper-containing oxidoreductase signal peptide protein in Sinorhizobium meliloti, respectively. ORF3 and ORF4 exhibited 23% identity to the gene encoding a cation efflux system membrane protein, CzcC, and 62% identity to the gene encoding a putative copper-containing oxidoreductase protein, respectively. The latter two ORFs were determined to be induced following exposure to low concentrations of copper, while addition of Co, Cd, or Zn resulted in no significant induction. PCR analysis of 51 pepper and 34 tomato copper-resistant X. campestris pv. vesicatoria strains collected from several regions in Taiwan between 1987 and 2000 and nine copper-resistant strains from the United States and South America showed that successful amplification of DNA was obtained only for strain XvP26. The organization of this set of copper resistance genes appears to be uncommon, and the set appears to occur rarely in X. campestris pv. vesicatoria.

Characterization ofcopABCDoperon from a copper-sensitivePseudomonasputidastrain

We describe an operon, copABCD, that encodes copper-binding and sequestering proteins for copper homeostasis in the copper-sensitive strain Pseudomonas putida PNL-MK25. This is the second operon characterized as being involved in copper homeostasis, in addition to a P1-type ATPase encoded by cueAR, which was previously shown to be active in the same strain. In this study, 3 copper-responsive mutants were obtained through mini-Tn5::gfp mutagenesis and were found to exhibit reduced tolerance to copper. Sequencing analysis of the transposon-tagged region in the 3 mutants revealed insertions in 2 genes of an operon homologous to the copABCD of P. syringae and pcoABCD of Escherichia coli. Gene expression studies demonstrated that the P. putida copABCD is inducible starting from 3 micromol/L copper levels. Copper-sensitivity studies revealed that the tolerance of the mutant strains was reduced only marginally (only 0.16-fold) in comparison to a 6-fold reduced tolerance of the cueAR mutant. Thus, the cop operon in this strain has a minimal role when compared with its role both in other copper-resistant strains, such as P. syringae pv. syringae, and in the cueAR operon of the same strain. We propose that the reduced function of the copABCD operon is likely to be due to the presence of fewer metal-binding domains in the encoded proteins.

Regulation of resistance to copper in Xanthomonas axonopodis pv. vesicatoria.

Copper-resistant strains of Xanthomonas axonopodis pv. vesicatoria were previously shown to carry plasmid-borne copper resistance genes related to the cop and pco operons of Pseudomonas syringae and Escherichia coli, respectively. However, instead of the two-component (copRS and pcoRS) systems determining copper-inducible expression of the operons in P. syringae and E. coli, a novel open reading frame, copL, was found to be required for copper-inducible expression of the downstream multicopper oxidase copA in X. axonopodis. copL encodes a predicted protein product of 122 amino acids that is rich in histidine and cysteine residues, suggesting a possible direct interaction with copper. Deletions or frameshift mutations within copL, as well as an amino acid substitution generated at the putative start codon of copL, caused a loss of copper-inducible transcriptional activation of copA. A nonpolar insertion of a kanamycin resistance gene in copL resulted in copper sensitivity in the wild-type strain. However, repeated attempts to complement copL mutations in trans failed. Analysis of the genomic sequence databases shows that there are copL homologs upstream of copAB genes in X. axonopodis pv. citri, X. campestris pv. campestris, and Xylella fastidiosa. The cloned promoter area upstream of copA in X. axonopodis pv. vesicatoria did not function in Pseudomonas syringae or in E. coli, nor did the P. syringae cop promoter function in Xanthomonas. However, a transcriptional fusion of the Xanthomonas cop promoter with the Pseudomonas copABCDRS was able to confer resistance to copper in Xanthomonas, showing divergence in the mechanisms of regulation of the resistance to copper in phytopathogenic bacteria.

Nucleotide Sequence and Organization of Copper Resistance Genes from Pseudomonas syringae pv. actinidiae

Copper-containing bactericides have been used to control bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae. However, the efficacy of copper has been reduced by the occurrence of copper-resistant strains. Analysis of the DNA sequence of a cluster region containing the copper-resistance genes from P. syringae pv. actinidiae suggested the presence of three possible different systems for copper resistance: copper-trapping, copper-efflux and copper-transport systems. Transposon insertional inactivation analysis indicated that the copper-trapping system was essential for copper resistance.

Sensibilidade a cobre, estreptomicina e oxitetraciclina em Xanthomonas spp. associadas à mancha-bacteriana do tomate para processamento industrial

Apesar de amplamente empregados em lavouras de tomate para processamento industrial no Brasil, fungicidas cúpricos e antibióticos registrados para uso agrícola nem sempre resultam em controle eficiente das bacterioses que afetam a cultura. O aparecimento de estirpes resistentes é uma das causas dessa baixa eficiência. Avaliou-se, in vitro, a sensibilidade a cobre, estreptomicina e oxitetraciclina de 389 isolados de Xanthomonas spp. associadas à mancha-bacteriana do tomateiro, sendo 92 de X. axonopodis pv. vesicatoria (60 do grupo "A"/raça T1 e 32 do "C"/raça T3), 93 de X. vesicatoria (grupo "B"/raça T2) e 204 de X. gardneri (grupo "D"/raça T2). Os isolados foram obtidos de plantas doentes em campos comerciais de tomate para processamento industrial nos estados de Goiás, Minas Gerais, Pernambuco e Bahia, nos anos de 1995 a 1998 e em 2000. Alíquotas de 5 ml de suspensões bacterianas foram depositadas em meio Nutriente-Ágar suplementado com sulfato de cobre, nas concentrações de 50 e 200 µg/ml; sulfato de estreptomicina, a 25 e 200 µg/ml e cloridrato de oxitetraciclina, a 25 µg/ml. Nenhum isolado foi resistente a oxitetraciclina, como também nenhum foi resistente ao cobre na concentração de 200 µg/ml do sulfato de cobre. No entanto, houve diferença entre isolados quanto à sensibilidade ao sulfato de cobre na concentração de 50 µg/ml e ao sulfato de estreptomicina nas duas concentrações empregadas. As freqüências de isolados de X. gardneri, X. axonopodis pv. vesicatoria (grupos "A" e "C") e X. vesicatoria resistentes à estreptomicina (25 µg/ml do produto usado) foram, respectivamente, 98%, 38% e 2%, ao passo que, ao cobre, foram, respectivamente, 48%, 4% e 74%. Todos os isolados do grupo "C" foram sensíveis à estreptomicina e 97% sensíveis ao cobre.

Copper Resistance in Pseudomonas syringae Strains Isolated from Mango Is Encoded Mainly by Plasmids

ABSTRACT Bacterial apical necrosis of mango, elicited by Pseudomonas syringae pv. syringae, limits fruit production in southern Spain and Portugal. Examination of a collection of P. syringae pv. syringae isolates for copper resistance showed that 59% were resistant to cupric sulfate. The survey of a mango orchard revealed an increase in frequencies of copper-resistant bacteria after repeated treatments with Bordeaux mixture. These data suggest that selection of copper-resistant strains could be a major reason for control failures following management with copper bactericides. Most copper-resistant isolates harbored plasmids, although the majority of them contained a 62-kb plasmid that also was present in copper-sensitive strains. The 62-kb plasmids were differentiated by restriction enzyme analysis and hybridization to copABCD DNA. The most frequently found copper-resistant plasmid type (62.1) was transferable by conjugation. Southern blot hybridizations showed that genetic determinants partially homologous to copABCD were present in all the copper-resistant strains examined, and usually were associated with plasmids; these determinants were not detected in copper-sensitive strains. The selective pressure exerted by copper bactericide sprays on the diversity of copper resistance determinants in bacterial populations of mango is discussed.

Similarity between Copper Resistance Genes from Pseudomonas syringae pv. actinidiae and P. syringae pv. tomato

Twenty-eight strains of Pseudomonas syringae pv. actinidiae isolated in 1984, 1987 and 1988 from kiwifruit orchards in Japan were tested for their resistance to copper sulfate. All strains isolated in 1984 were copper sensitive with a minimum inhibitory concentration (MIC) of cupric sulfate of 0.75 mM. However, some strains isolated in 1987 and 1988 were resistant, with the MIC ranging from 2.25 to 3.0 mM. All copper-resistant strains contained at least one of two plasmids, pPaCul (about 70.5 kb) or pPaCu2 (about 280 kb), or both. In a copper-resistant strain Pa429, the location of the copper-resistance gene(s) was examined by insertional inactivation with Tn5. The MIC of copper sulfate in the copper-sensitive mutant obtained by Tn5 tagging decreased from 2.75 to 0.75 mM. The 14.5 kb BamHI fragment, designated pPaCuB14, containing the same locus mutagenized with Tn5 was cloned from pPaCu1. However, pPaCuB14 did not confer copper resistance in the transformant of copper-sensitive strain Pa21R, suggesting that this clone did not contain a full set of copper-resistance gene(s). Then a cosmid library of pPaCu1 was constructed and six cosmid clones hybridized with pPaCuB14 were selected. One of the six cosmids, designated pPaCuC1, conferred a near wild-type level of copper resistance in the transformant of the copper-sensitive strain. pPaCuC1 had a homologous region that hybridized with all of the PCR-amplifled fragments of copA, copB, copR, and copS genes of P. syringae pv. tomato. DNA sequence analysis of the homologous region revealed the existence of four open reading frames (ORF A, B, R and S) oriented in the same direction. The predicted amino acid sequences of ORF A, B, R and S had 80, 70, 97 and 95% identity with CopA, B, R and S of P. syringae pv. tomato, respectively.

Leading Edge of Plant Protection for Walnuts

English walnut (Juglans regia) producers in California compete with many insect and disease pests to produce an acceptable crop. Traditional control strategies work reasonably well for most pests. However, environmental concerns, loss of certain pesticides and new or impending regulations threaten the use of many traditional techniques for control of many of the pests. Codling moth (Cydia pomonella), walnut husk fly (Rhagoletis completa), and walnut aphid (Chromaphis juglandicola) are the major insects that affect California walnut production. Control strategies that use integrated pest management programs, beneficial insects, mating disruption, insect growth regulators, improved monitoring techniques and precise treatment timing based on the insect's life cycle are leading edge techniques currently available for insect control in walnuts. Major diseases include walnut blight (Xanthomonas campestris pv. juglandis), crown gall (Agrobacterium tumefaciens) and crown and root rot (Phytophthora spp). Both copper resistant and copper sensitive strains of the walnut blight bacterium are best controlled with combinations of copper bactericides and maneb instead of copper materials alone. A new computer model, Xanthocast, used to forecast the need for walnut blight treatment is under evaluation. Crown gall is managed using a preplant biological control agent and a heat treatment to eradicate existing galls. Phytophthora crown and root rot is dealt with primarily by site selection, irrigation management and rootstock selection.

Copper uptake and its compartmentalization in Pseudomonas aeruginosa strains: Chemical nature of cellular metal

Copper-sensitive (Cus) and copper-resistant (Cur) strains of Pseudomonas aeruginosa were characterized in terms of Cu2+ sensitivity, uptake and its compartmentalization in the possible cell sectors. Minimum inhibitory concentrations (MICs) of Cu2+ for the Cur strain (3.2 mM and 0.12 mM in enriched- and in minimal-medium, respectively) were almost 5-fold higher over that of its sensitive counterpart. While Cus strain accumulated Cu2+ to a maximum of 1.8 μ mol mg−1 protein, Cur strain increased it to 2.37 μmol mg−1 protein. Both the strains also demonstrated energy- and pH-dependent Cu2+ uptake through the broad-substrate range divalent cation (Zn2+, Mg2+, Co2+) uptake system as well as through the system specific for Cu2+. Cell-fractionation study revealed that in Cur strain, periplasm and membrane are the main Cu2+ binding sites, whereas, in case of Cus strain, it is the cytoplasm. The overall observations indicate that the Cur strain restricted Cu2+ sequestration exterior to the cytoplasm as the possible strategy for Cu-resistance. The chemical nature of Cu2+ deposition in the respective strains was also ascertained by X-ray powder diffraction analysis.

Bacterial Spot of Tomato and Pepper on Four East Caribbean Islands: Races, Their Abundance, Distribution, Aggressiveness, and Prospects for Control.

A total of 5,134 strains of Xanthomonas campestris pv. vesicatoria obtained from diseased pepper and tomato fruits at 22 diverse locations on the East Caribbean islands of Antigua, St. Christopher, St. Lucia, and Grenada were assessed for pathogenicity, taxonomic group phenotypes, and sensitivity to copper, zinc, and streptomycin. Altogether, 15 known races, namely T1, T2, P0T1, P0T2, P1T1, P1T2, P2T1, P2T2, P3T1, P3T2, P4T2, P5T2, P5T3, P6T2, and P6T3, were detected. Races T1, P0T1, P0T2, P1T2, P2T1, and P3T1 were common to all islands except St. Lucia. St. Lucia had races P2T2, P3T2, P4T2, and P6T2 in common with Grenada and two races each from among the four pathotypes in common with Antigua and St. Lucia. Races T1, P1T2, P3T1, and P3T2 were the most abundant strains of the bacterium in Antigua, whereas the two latter pathotypes, as well as races P0T1 and P2T1, were among the most prevalent strains in St. Christopher. In contrast, races P6T2 and P5T2 predominated in St. Lucia, and P6T2, P1T2, and P3T2 were the abundant pathotypes in Grenada. Generally, the largest bacterial spot fruit lesions were associated with the predominant races on each island, and the smallest lesions were generally linked to races capable of overcoming gene Bs2. Only these latter races were similar to group B strains of X. campestris pv. vesicatoria with respect to the presence of β-protein in their cellular protein profiles, ability to hydrolyze starch, and inability to oxidize cis-aconitate. Other race types tested resembled group A strains of the bacterium in their ability to utilize cis-aconitate, inability to hydrolyze starch and pectate, and the presence of the α-protein in profiles of cellular proteins. Copper-resistant strains of X. campestris pv. vesi-catoria constitute 8.7 to 10.6% of the pathogen collections from Antigua and St. Christopher and 44.4 and 66.7% of pathotypes from St. Lucia and Grenada, respectively. Almost all strains were sensitive to zinc. Streptomycin resistance was observed among 62% of the strains in St. Christopher and Grenada and 62.8 to 83.6% of those in Antigua and St. Lucia.

Effect of Copper Bactericides on Copper-Resistant and -Sensitive Strains of Pseudomonas syringae pv. syringae.

Fourteen formulations of copper-based bactericides were evaluated for their efficacy in reducing populations of copper-resistant and -sensitive strains of Pseudomonas syringae pv. syringae growing on tissue-cultured lilac and of copper-sensitive strains of this pathogen on field-grown lilac. The amount of free cupric ions (Cu2+) in solution was the only predictor of formulation efficacy, but this variable could not be estimated from the metallic copper content of the product. Relative to nontreated controls, all copper-based bactericides reduced the population size of copper-sensitive strains by 50%, but only cupric hydroxide mixed with mancozeb or ferric chloride reduced the population size of copper-resistant strains by an equivalent amount. Several noncopper bactericides, including streptomycin-sulfate, caused only small reductions in bacterial populations on tissue-cultured or field-grown lilacs. In the field, two applications of cupric hydroxide (wettable powder) when plant growth stages were at dormant (mid-February) and delayed dormant (late February) provided better control than either one or no treatments.