Spot Of Pepper Research Articles

Copper Tolerance in Australian Populations of Xanthomonas campestris pv. vesicatoria Contributes to Poor Field Control of Bacterial Spot of Pepper.

Many Australian pepper producers have reported poor control of bacterial spot of pepper (caused by Xanthomonas campestris pv. vesicatoria) despite using copper bactericides at recommended rates. This prompted us to investigate whether copper-tolerant strains of the pathogen are present in Australia and whether they are a contributing factor to poor control. We screened strains of X. campestris pv. vesicatoria in the laboratory, in broths containing different concentrations of CuSO4, and established the maximum copper concentration at which each strain could grow. About one in four strains (75 total) collected between 1999 and 2000 tolerated ≥1.0 mM CuSO4 and could be considered copper tolerant. Only one strain (of 12) collected before 1987 could tolerate 1.0 mM, and comparison of the two populations by fitting regression models revealed that the mortality of strains in the two populations differed significantly across all concentrations of copper. It was necessary to apply higher rates of copper to strains collected between 1999 and 2000 to achieve mortality levels equivalent to those in the older population. This is strong evidence that the prevalence of copper-tolerant strains has increased in Australian populations. We also assessed whether copper-tolerant strains may increase substantially in a field population of X. campestris pv. vesicatoria when copper is repeatedly sprayed. In the field, the proportion of copper-tolerant strains increased after 12 weekly sprays of copper, and they were very prevalent in the population after 21 sprays. This is the first report of copper tolerance in Australian populations of X. campestris pv. vesicatoria.

Development of a sensitive ELISA using three monoclonal antibodies against lipopolysaccharides to detect Xanthomonas campestris pv. vesicatoria, the causal agent of bacterial spot of tomato and pepper

Bacterial spot, caused by Xanthomonas campestris pv. vesicatoria (Doidge 1920) Dye 1978 (Xcv), is responsible for severe production losses in tomato and pepper. Three specific monoclonal antibodies (MABs), 7AH10, 5HB3, and 4AD2, which are reactive to lipopolysaccharides of the bacteria, were tested in three kinds of enzyme-linked immunosorbent assays (ELISAs). The most sensitive ELISA was a competitive one able to detect populations of Xcv as low as 103–104 cfu/ml. Bacterial growth in artificially inoculated tomato and pepper plants could be successfully monitored, and assays on field-collected samples reconfirmed the diagnostic utility of the MABs. Studies on the accessibility of the MABs to their lipopolysaccharide epitopes confirmed that sample preparation can be improved to further increase the sensitivity of the assay. Immunoblotting of differential extracts of the bacterial cells and immunoelectron microscopy demonstrated that the epitopes were present throughout the cell wall and involved in complexes that can be loosened through the action of proteinase K or lysozyme.

Tree vigour influences disease susceptibility of 'Hass' avocado fruits

Differences in tree vigour as a result of feeder root destruction by Phytophthora cinnamomi were found to significantly (P < 0.05) influence disease susceptibility, fruit ripening rates and fruit size of ‘Hass’ avocado. Fruits from root rot-affected, non-vigorous trees had less anthracnose and took longer to ripen. However, they were probably unmarketable due to their small fruit size compared with fruits from healthy vigorous trees. Fruits from non-vigorous trees also had less pepper spot than vigorous trees, but only on the inside of the tree canopy. The increased disease resistance of fruits from non-vigorous trees was related to a 40% increase in the concentration of Ca in the fruit flesh.

Bacterial Spot of Tomato and Pepper Caused by Xanthomonas axonopodis pv. vesicatoria in the Western Mediterranean Region of Turkey.

Xanthomonas axonopodis pv. vesicatoria, causal agent of bacterial spot of tomato (Lycopersicon esculentum L.) and sweet pepper (Capsicum annuum L.) was isolated from tomato and pepper plants in greenhouse production in the Province of Antalya, in southwestern Turkey. Disease incidence was less than 4% of plants observed in 2001 and ranged from 1 to 20% in 2002. Eleven seedling-producing companies and 26 greenhouses that produce tomato and pepper were surveyed during the rainy seasons of 2001 and 2002. The increase in disease incidence in 2002 is an indication that this disease is becoming more prevalent on tomato and pepper plants grown in greenhouses in southwestern Turkey. A gram-negative bacterium producing yellow-pigmented colonies on nutrient agar was consistently isolated from brown, circular spots on leaflets of tomato and sweet pepper seedlings. Five isolates were pathogenic on commercial cultivars of tomato and pepper when bacterial suspensions (108 CFU/ml) were infiltrated into the intercellular spaces of leaves to determine race by using procedures described by Bouzar et al. (1). All the isolates produced hypersensitive reaction responses on tomato genotype cv. Hawaii 7998 and pepper genotype cvs. 20 R and 30 R and were designated tomato race 1 pepper race 1 (T1P1) (1). Fatty acid analysis of the strains identified them as X. axonopodis vesicatoria with similarity index values of 0.872 to 0.933. In addition, the strains were tested with X. axonopodis vesicatoria-specific polymerase chain reaction primers (RST 2/3 and RST 9/10) (2). The isolates were determined to be X. axonopodis vesicatoria. Although bacterial spot of tomato has been suspected in Turkey for a number of years, to our knowledge, this is the first report of the bacterium on tomato.

고추 갈색점무늬병원균 (Cercospora capsici)의 배양특성과 다량 포자형성법

High sporulation method and cultural characteristics of Cercospora capsici causing Cercospora leaf spot of pepper were examined. Optimum temperature for mycelial growth of Cercospora capsici was . The fungus did not grow below and over . Optimum pH for mycelial growth was pH 4.0~pH 8.0. Mycelial growth was not influenced by light. C. capsici sporulated well on pepper leaf agar (5g/l). A standard method of sporulation established was as follows. The mycelial plugs were ground with some water in motar with pestle. The mycelial suspension was smeared on the surface of medium and incubated for 2~3 days at . The culture surface was lightly scraped with a brush after adding 1 ml of sterile water to stimulate sporulation and further incubated for 2~3 days.

Effect of foliar applications of neem oil and fish emulsion on bacterial spot and yield of tomatoes and peppers

Foliar applications of neem oil and fish emulsion, derived from neem seed and menhaden fish, respectively, were tested for their ability to reduce bacterial spot of tomato and bell pepper under both greenhouse and field conditions. Greenhouse-grown tomato and pepper plants sprayed with aqueous suspensions (0.5%, v/v) of neem oil or fish emulsion and then inoculated with Xanthomonas campestris pv. vesicatoria showed less disease symptoms than the water-treated controls. Weekly foliar sprays of neem oil and fish emulsion reduced disease severity on the foliage of inoculated field-grown tomato and pepper plants in both years of a two-year study. The disease incidence on the fruit of these plants was reduced but the effect was not always statistically significant. However, the number of lesions per pepper fruit were consistently lower with these treatments. Fish emulsion increased healthy and total fruit yield of tomatoes in 2000 and healthy fruit yield of peppers in 2001, whereas neem oil increased the yield of disease-free peppers in both years. Neem oil and fish emulsion had no observable phytotoxic effect on tomato or pepper foliage in the field. These results suggest that disease-management programs for bacterial spot may be enhanced by including foliar sprays of these products.

Getting across--bacterial type III effector proteins on their way to the plant cell.

Pathogenicity of most Gram-negative bacterial plant pathogens depends on hrp (hypersensitive response and pathogenicity) genes, which control the ability to cause disease and to elicit specific defense responses in resistant plants. hrp genes encode a specialized type III secretion (TTS) system that mediates the vectorial delivery of bacterial effector proteins across both bacterial membranes as well as across the eukaryotic plasma membrane into the host cell cytosol. One well-studied effector protein is AvrBs3 from Xanthomonas campestris pv. vesicatoria, the causal agent of bacterial spot in pepper and tomato. AvrBs3 induces hypertrophy symptoms in susceptible plants and triggers a resistance gene-specific cell death reaction in resistant plants. Intriguingly, AvrBs3 has characteristic features of eukaryotic transcription factors, suggesting that it modulates the host's transcriptome. Here, we discuss the TTS system of X.campestris pv. vesicatoria in the light of current knowledge on type III-dependent protein secretion in plant pathogenic bacteria.

A Monocot Plant Identified as an Alternate Host of the Causal Agent of Bacterial Spot of Tomato and Pepper

Xanthomonas campestris pv. vesicatoria (Xcv) recovered from Commelina benghalensis L., caused bacterial spot disease in cultivars of pepper and tomato susceptible to the pathogen. This is the first reported case of a dicot-infecting Xc pathovar infecting a monocot plant, represented here by a member of the Family Commelinaceae. Laboratory strains of the pathogen that included 81-23, 81-23M13, 82:4, 2595, and P6AD4, known to be pathogenic to pepper and tomato, promoted bacterial spot symptoms on leaves of C. benghalensis L. Of the 63 field isolates recovered from infected C. benghalensis L., 30 gave biochemical and physiological reactions consistent with Xcv pathogens, whereas 10 of the latter promoted bacterial spot disease in the test cultivars resulting in the identification of seven pathogenic races, including P2, P5, P6, P5T1, P5T2, P6T2, and P6T3. Bacterial spot disease symptoms developed on stems only when C. benghalensis L. was spray-inoculated with strains 81-23, 81-23M13, and P6AD4. Bacterial concentration increased in planta by as much as 103 per lesion of the leaf, whereas growth of the same strains was restricted in the stem of this weed. Growth of these three strains was, however, significantly (P ≤ 0.05) lower on NYGA amended with C. benghalensis L. stem extract than on NYGA amended with leaf extract. The ability of the bacterial spot pathogen to infect the stem of C. benghalensis L. has serious implications for management of bacterial spot disease in fields populated with this weed since stems of this plant infected with the pathogen continue to grow vegetatively and disperse throughout all fields in which it is found.

Pepper spot: A preharvest disease of lychee caused by Colletotrichum gloeosporioides

Pepper spot: A preharvest disease of lychee caused by Colletotrichum gloeosporioides

Bacterial spot (Xanthomonas campestris pv. vesicatoria ) of tomato and sweet pepper in Tanzania

Bacterial spot of tomato (Lycopersicon esculentum) and sweet pepper (Capsicum annuum) is recorded from several countries of eastern and southern Africa, including Ethiopia, Kenya, Malawi, Mozambique and South Africa. With the growing importance of solanaceous cash crops in Tanzania, particularly tomato, it was important to confirm the findings of preliminary reports of the possible presence of the pathogen and to record it officially. It was also desirable to assess the degree of contamination of seed as potentially the most significant source of inoculum. Field surveys during the rainy seasons of 1997 and 1998 showed that bacterial spot could be found in tomato and sweet pepper fields in all the mainland vegetable regions of the northern and southern highlands, but not in Zanzibar. In fields of tomato surveyed (59 in 1997, 50 in 1998) in which bacterial spot could be seen, incidence (percentage of plants with symptoms) varied greatly between years and fields (from ,5% to .90%). In pepper, incidence was never greater than 5% (10 fields surveyed in 1997, three in 1998). Xanthomonas campestris pv. vesicatoria (Xcv) suspected from symptoms on tomato and sweet pepper fruit was confirmed by isolation on semi-selective media including Tween B (McGuire et al., 1986), followed by biochemical tests for Xanthomonas and pathogenicity tests on tomato. Although the name X. c. pv. vesicatoria remains a valid taxonomic name, it has recently been proposed for reclassification into three separate species (Jones et al., 2000). However, available data for the Tanzanian isolates are not sufficient for them to be allocated to the newly proposed taxa. In some cases, bacterial spots masked symptoms of Clavibacter michiganensis ssp. michiganensis which was also present (Black et al., 1999). For detection of Xcv in seed, extraction methods recommended for quarantine purposes were used (Anon., 1992). Using dilution plating, Xcv was found in five out of 26 samples of farmers' saved seed, was absent from 12 commercial tomato seed lots and present in two out of three commercial pepper seed lots sampled.

UDP-Glucose Dehydrogenase Gene of Xanthomonas campestris Is Required for Virulence

Xanthomonas campestris pv. campestris (Xc) is the casual agent of black rot in crucifers. The Xc gene (udgH) coding for UDP-glucose dehydrogenase, an enzyme catalyzing the conversion of UDP-glucose to UDP-glucuronic acid, was previously shown to be required for the biosynthesis of xanthan gum, a substance necessary for the bacterium to cause disease. In this study, the transcription start site of the udgH was determined and the promoter activity monitored by the xylE reporter system indicated that expression of the udgH increases following cell growth and that the udgH gene may possess a second promoter that is responsive to stationary-phase change retaining high levels of expression. Results of Southern hybridization suggest that the udgH gene may be ubiquitous in Xanthomonas, coincident with the notion that members of this genus are capable of xanthan gum biosynthesis. Mutation of the udgH gene in Xc and X. campestris pv. vesicatoria, the casual agent of leaf spot in pepper and tomato, was found to cause a loss of virulence.

Optimisation of inoculum production and incubation conditions for screening white clover for resistance to Leptosphaerulina trifolii

This study was conducted to investigate sporulation of Leptosphaerulina trifolii (Rost.) Petrak and to improve infection of white clover plants during experimental screening of germplasm for resistance to this ascomycete. Sporulation at 23 ± 2°C was greatest after 9 ± 1 days growth on V-8 juice agar under fluorescent and near-ultraviolet lights. Infection was greatly promoted by keeping leaf surfaces wet during the initial period of ascospore deposition. Increasing the period of ascospore deposition beyond 12 h did not significantly increase plant infection. The number of pepper spot lesions which appeared on leaves was significantly correlated with the number of ascospores released by sporulating cultures suspended over plants during the spore deposition period. More leaf spots were produced when the temperature was 25°C during ascospore deposition and 20°C during incubation than when a regime of 20/15°C was used.

Bacterial spot of pepper and tomato

Bacterial spot of pepper and tomato

Pepper spot: a new preharvest Colletotrichum disease of avocado cv. Hass.

Pepper spot of avocado cv. Hass, an undescribed preharvest disease, was found to be caused by Colletotrichum gloeosporioides.

Development of Bacterial Spot on Near-Isogenic Lines of Bell Pepper Carrying Gene Pyramids Composed of Defeated Major Resistance Genes

ABSTRACT Disease severity caused by races 1 through 6 of Xanthomonas campestris pv. vesicatoria on eight near-isogenic lines (isolines) of Early Calwonder (ECW) with three major resistance genes (Bs1, Bs2, and Bs3) in different combinations was evaluated in the greenhouse and field. Strains representing races 1, 3, 4, and 6 caused similar high levels of disease severity, followed by races 2 and 5 on susceptible ECW. Race 3 caused severe disease on all isolines lacking resistance gene Bs2. Race 4, which defeats Bs1 and Bs2, caused less disease on isoline ECW-12R (carries Bs1 + Bs2), than on isolines ECW, ECW-10R (carries Bs1), and ECW-20R (carries Bs2). Similar results were obtained with race 4 strains in field studies conducted during 1997 and 1998. In greenhouse studies, race 6, which defeats all three major genes, caused less disease on isoline ECW-13R (carries Bs1 + Bs3) and ECW-123R (carries Bs1 + Bs2 + Bs3) than on isolines ECW, ECW-10R, ECW-20R, and ECW-30R (carries Bs3), but not on ECW-23R (carries Bs2 + Bs3). In greenhouse studies with commercial hybrids, strains of races 4 and 6 caused less disease on Boynton Bell (carries Bs1 + Bs2) than on Camelot (carries no known resistance genes), King Arthur (carries Bs1), and X3R Camelot (carries Bs2). Race 6 caused less disease on hybrid R6015 (carries Bs1 + Bs2 + Bs3) and Sentinel (carries Bs1 + Bs3) than on Camelot. Residual effects were not as evident in field studies with race 6 strains. Defeated major resistance genes deployed in specific gene combinations (i.e., gene pyramids) were associated with less area under the disease progress curve than when genes were deployed individually in isolines of ECW or commercial hybrids. Successful management of bacterial spot of pepper is achieved incrementally by integrating multiple tactics. Although there is evidence of residual effects from defeated genes, these effects alone likely will not provide acceptable bacterial spot control in commercial production fields. However, when combined with sanitation practices and a judicious spray program, pyramids of defeated resistance genes may aid in reducing the risk of major losses due to bacterial spot.

Races of Xanthomonas campestris pv. vesicatoria overcoming the gene Bs2 for bacterial spot resistance in pepper, prevalent on Capsicum chinense in Barbados and Grenada and weakly pathogenic on bell pepper and tomato in the field

A total of 404 isolates of Xanthomonas campestris pv. vesicatoria, obtained from Capsicum chinense cv. West Indian Red grown in Barbados and Grenada, were differentiated into pathogenic races, and of these, 96 were tested also for selected taxonomic group phenotypes. The response of C. chinense to infection by several X. campestris pv. vesicatoria races and the contribution of races isolated from this cultivar to severity of bacterial spot of bell pepper and tomato were also investigated. P4T2, P5T2 and P6T2 were the predominant races of X. campestris pv. vesicatoria isolated from C. chinense grown in Grenada, whereas nine races (T1, P4, P6, P0T2, P1T2, P4T1, P4T2, P6T1 and P6T2) were isolated in Barbados. Race P4T2 comprised 46.0 and 71.4% of the isolates from Barbados and Grenada, respectively. The 96 isolates, all of which overcame resistance conferred by the gene Bs2, shared taxonomic group B strain characteristics, including the presence of the β‐protein band, positive amylolytic activity and inability to oxidize cis‐aconitate. The C. chinense cv. West Indian Red was susceptible only to races of X. campestris pv. vesicatoria that can overcome Bs2 gene resistance. Of six such races identified in Barbados, only P4T1, P4T2 and P6T1 affected bacterial spot‐susceptible bell pepper or tomato in the field, and they amounted to only 1.5–2.1% of each sample of isolates from these plant species. Moreover, they were confined to the smallest bacterial spot lesions. Bell pepper was most severely affected by combinations of races T1 with P3T2 and T2 with P0T1, and tomato by race T1 only and combinations of races P0T1 with P0T2 and P1T1 with P1T0, all of which prevailed in the field despite selection against them by C. chinense cv. West Indian Red.

Variety and environment affect pepper spot infection on apple

Variety and environment affect pepper spot infection on apple

First Observation of Xanthomonas campestris pv. vesicatoria Race T2P7 Isolated from Pepper in the Philippines

Thirteen strains of Xanthomonas campestris pv. vesicatoria, causal agent of bacterial spot of pepper (Capsicum spp.) and tomato (Lycopersicum spp.), were isolated from six different pepper fields in the vicinity of Bongabon, Luzon, the Philippines. The strains were characterized based on sensitivity to copper and streptomycin, physiological tests, analysis of whole cell fatty acids (fatty acid methyl ester; FAME), serology, amplification of the 16S-23S rDNA spacer region, pathogenicity, and virulence on pepper and tomato differential genotypes as previously described (1,2). All of the Philippine strains were copper resistant (50 μg/ml), and streptomycin sensitive (20 μg /ml). None of the strains were pectolytic or amylolytic. FAME analysis showed that all strains had similar fatty acid profiles, and matched the strains to X. campestris (similarity indices [S.I.] = 0.186-0.455). With the universal primers 4F/7R, a DNA fragment (680 bp) was amplified from 16S-23S rDNA spacer regions of all Philippine strains. Serological fingerprints of the strains with a set of eight monoclonal antibodies (MAbs) in indirect enzyme-linked immunosorbent assay showed that all Philippine strains were serovar A1. Existence of the avrRxv gene in X. campestris pv. vesicatoria race T1 strains was also confirmed for all Philippine strains by amplifying a DNA fragment (approximately 0.7 kb) with the primer set RST 27/28. This is genetic evidence for race identity of the Philippine strains with T1. However, hypersensitive test results on pepper and tomato differential lines identified the Philippine strains as T2P7. These results showed that X. campestris pv. vesicatoria strains may contain the avrRxv gene, but it may not be functional. This is the first report of the observation of X. campestris pv. vesicatoria race T2P7 on pepper.

Diversity among xanthomonads pathogenic on pepper and tomato.

Xanthomonas campestris pv. vesicatoria, causal agent of bacterial spot of tomato and pepper, had been considered for nearly 70 years to be a relatively homogeneous organism. However, in the past decade this bacterium was determined to be composed of two genetically and phenotypically distinct groups. The two groups, designated A and B, were distinguished based on amylolytic activity, expression of unique protein bands, reaction on differential hosts (tomato races T1 and T2), reaction patterns with monoclonal antibodies, DNA restriction profiles, and DNA:DNA hybridization. The A and B groups were placed into X. axonopodis pv. vesicatoria and X. vesicatoria, respectively. A third group, designated C, was pathogenically (race T3) and serologically distinct from A and B strains, and formed unique DNA restriction profiles. DNA:DNA hybridization data suggest that C is distinct but related to A strains and may represent a subspecies of A. A final group, designated D, consisted of X. gardneri, an organism identified in Yugoslavia in 1957, and also found in Costa Rica. Group D was determined to be genetically distinct from strains within the other two groups; it represents a third Xanthomonas species pathogenic on tomato and pepper.

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.