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At least 163 records · Page 9Linked to original sources
PubMed2000

Zoospore homing and infection events: effects of the biocontrol bacterium Burkholderia cepacia AMMDR1 on two oomycete pathogens of pea (Pisum sativum L.).

Burkholderia cepacia AMMDR1 is a biocontrol agent that protects pea and sweet corn seeds from Pythium damping-off in field experiments. The goal of this work was to understand the effect of B. cepacia AMMDR1 on Pythium aphanidermatum and Aphanomyces euteiches zoospore homing events and on infection of pea seeds or roots. In vitro, B. cepacia AMMDR1 caused zoospore lysis, prevented cyst germination, and inhibited germ tube growth of both oomycetes. B. cepacia AMMDR1 also reduced the attractiveness of seed exudates to Pythium zoospores to nondetectable levels. However, when present at high levels on seeds, B. cepacia AMMDR1 had little net effect on zoospore attraction, probably because it also enhanced seed exudation. Seed-applied B. cepacia AMMDR1 dramatically reduced the incidence of infection by Pythium zoospores in situ compared with an antibiosis-deficient Tn5 mutant strain. This mutant strain also decreased Pythium infection incidence to some extent, but only when the pathogen inoculum potential was low. B. cepacia AMMDR1 did not affect attraction of Aphanomyces zoospores or Aphanomyces root rot incidence. These results suggest that B. cepacia AMMDR1 controls P. aphanidermatum largely through antibiosis, but competition for zoospore-attracting compounds can contribute to the effect. Differences in suppression of Aphanomyces and Pythium are discussed in relation to differences in the ecology of the two pathogens.

Burkholderia cepacia↗
PubMed2002

Novel aspects of tomato root colonization and infection by Fusarium oxysporum f. sp. radicis-lycopersici revealed by confocal laser scanning microscopic analysis using the green fluorescent protein as a marker.

The fungus Fusarium oxysporum f. sp. radicis-lycopersici is the causal agent of tomato foot and root rot disease. The green fluorescent protein (GFP) was used to mark this fungus in order to visualize and analyze the colonization and infection processes in vivo. Transformation of F oxysporum f. sp. radicis-lycopersici was very efficient and gfp expression was stable for at least nine subcultures. Microscopic analysis of the transformants revealed homogeneity of the fluorescent signal, which was clearly visible in the hyphae as well as in the chlamydospores and conidia. To our knowledge, this is the first report in which this is shown. The transformation did not affect the pathogenicity. Using confocal laser scanning microscopy, colonization, infection, and disease development on tomato roots were visualized in detail and several new aspects of these processes were observed, such as (i) the complete colonization pattern of the tomato root system; (ii) the very first steps of contact between the fungus and the host, which takes place at the root hair zone by mingling and by the attachment of hyphae to the root hairs; (iii) the preferential colonization sites on the root surface, which are the grooves along the junctions of the epidermal cells; and (iv) the absence of specific infection sites, such as sites of emergence of secondary roots, root tips, or wounded tissue, and the absence of specific infection structures, such as appressoria. The results of this work prove that the use of GFP as a marker for F. oxysporum f. sp. radicis-lycopersici is a convenient, fast, and effective approach for studying plant-fungus interactions.

Fusarium↗
PubMed2006

Two novel MvaT-like global regulators control exoproduct formation and biocontrol activity in root-associated Pseudomonas fluorescens CHA0.

Pseudomonas fluorescens CHA0 protects various crop plants against root diseases caused by pathogenic fungi. Among a range of exoproducts excreted by strain CHA0, the antifungal compounds 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT) are particularly relevant to the strain's biocontrol potential. Here, we report on the characterization of MvaT and MvaV as novel regulators of biocontrol activity in strain CHA0. We establish the two proteins as further members of an emerging family of MvaT-like regulators in pseudomonads that are structurally and functionally related to the DNA-binding protein H-NS. In mvaT and mvaV in frame-deletion mutants of strain CHA0, PLT production was enhanced about four- and 1.5-fold, respectively, whereas DAPG production remained at wild-type levels. Remarkably, PLT production was increased up to 20-fold in an mvaT mvaV double mutant. DAPG biosynthesis was almost completely repressed in this mutant. The effects on antibiotic production could be confirmed by following expression of gfp-based reporter fusions to the corresponding biosynthetic genes. MvaT and MvaV also influenced levels of other exoproducts, motility, and physicochemical cell-surface properties to various extents. Compared with the wild type, mvaT and mvaV mutants had an about 20% reduced capacity (in terms of plant fresh weight) to protect cucumber from a root rot caused by Pythium ultimum. Biocontrol activity was nearly completely abolished in the double mutant Our findings indicate that MvaT and MvaV act together as further global regulatory elements in the complex network controlling expression of biocontrol traits in plant-beneficial pseudomonads.

Amino Acid Sequence↗
PubMed2004

Proteomic approach: identification of Medicago truncatula proteins induced in roots after infection with the pathogenic oomycete Aphanomyces euteiches.

The legume root rot disease caused by the oomycete pathogen Aphanomyces euteiches is one major yield reducing factor in legume crop production. A comparative proteomic approach was carried out in order to identify proteins of the model legume Medicago truncatula which are regulated after an infection with A. euteiches . Several proteins were identified by two dimensional gel electrophoresis to be differentially expressed after pathogen challenge. Densitometric evaluation of expression values showed different regulation during the time-course analysed. Proteins regulated during the infection were identified by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Among the differentially expressed proteins, two encoded putative cell wall proteins and two were designated as small heat shock proteins. Furthermore, an isoform of the chalcone-O-methyltransferase was found to be increased in infected roots. The majority of induced proteins belonged to the family of class 10 of pathogenesis related proteins (PR10). Previously, various PR10-like proteins have been shown to be regulated by general stress or abscisic acid (ABA). Therefore, these proteins were further investigated concerning their regulation in response to drought stress and exogenous ABA-application. Complex regulation patterns were identified: three of the A. euteiches -induced PR10-like proteins were also induced by exogenous ABA- but none of them is induced after drought stress. In contrast, three of these proteins are down-regulated by drought stress. Hence, the strong expression of different PR10-family members and their regulation profiles indicates that this set of proteins plays a major role during root adaptations to various stress conditions.

Abscisic Acid↗
PubMed2005

Disease suppression on greenhouse tomatoes using plant waste compost.

This study investigated the disease suppression abilities of a compost amendment that was added to the conventional growing medium, yellow cedar sawdust, used in most British Columbia vegetable greenhouses. The compost amendment was produced in a controlled, in-vessel process primarily from greenhouse crop waste materials. The pathogen and cultivar under study were Fusarium oxysporum f. sp. radicis-lycopersici (FORL) on Dombito (FORL-susceptible) beefsteak greenhouse tomatoes. Significant reduction of Fusarium crown and root rot was also realized in tomato seedlings by applying compost amendment from several different batches, as a seed cover or plug substitute. In a greenhouse trial, disease suppression using a mixture of 2:1 sawdust to amendment by volume was shown to be most effective. As a result, the tomato yield over a nine-month growing season was improved by 74% where the medium was deliberately infested with FORL.

Antibiosis↗
PubMed1980

The effect of the herbicide atrazine on rhizosphere microflora of broad bean plants, infested with Fusarium oxysporum f. fabae and Rhizoctonia solani.

The effect of the herbicide atrazine on Fusarium oxysporum f. fabae and Rhizoctonia solani, the causative agents of wilt and rot, respectively, as well as rhizosphere microflora of broad bean plants was studied. The herbicide was applied at intervals of 30, 20, 10, and 0 days before sowing. Atrazine application reduced both densities and per cent of infection of these two pathogenic fungi, R. solani, however, was sensitive to atrazine itself, while F. oxysporum was affected by atrazine by-products. Rhizosphere flora, i.e., total microbial flora, actinomycetes, phosphate-dissolving bacteria, and fungal flora, were not affected by atrazine, but were deleteriously reduced by its by-products at early stages of plant growth. However, rhizosphere flora attained the normal levels after atrazine by-products had completely disappeared from soil (1 month after application), except for actinomycetes. Therefore, it is recommended to apply atrazine within 20 days before sowing for weed control as well as for controlling wilt and root rot infestations.

Actinomycetaceae↗
PubMed2000

Citrus Blight and Other Diseases of Recalcitrant Etiology.

Several economically important diseases of unknown or recently determined cause are reviewed. Citrus blight (CB), first described over 100 years ago, was shown in 1984 to be transmitted by root-graft inoculations; the cause remains unknown and is controversial. Based on graft transmission, it is considered to be an infectious agent by some; others suggest that the cause of CB is abiotic. Citrus variegated chlorosis, although probably long present in Argentina, where it was considered to be a variant of CB, was identified as a specific disease and shown to be caused by a strain of Xylella fastidiosa after if reached epidemic levels in Brazil in 1987. Citrus psorosis, described in 1933 as the first virus disease of citrus, is perhaps one of the last to be characterized. In 1988, it was shown to be caused by a very unusual virus. The cause of lettuce big vein appears to be a viruslike agent that is transmitted by a soilborne fungus. Double-stranded RNAs were associated with the disease, suggesting it may be caused by an unidentified RNA virus. Rio Grande gummosis, dry rot root, peach tree short life, and some replant diseases may be diseases of complex etiology. Various microorganisms have been isolated from trees with these diseases, but the diseases may be attributable in part to environmental factors. Determination of the cause of these diseases of complex etiology has proven difficult, in part, because they affect only mature trees.

citrus psorosis↗
PubMed2005

Phenylacetic acid-producing Rhizoctonia solani represses the biosynthesis of nematicidal compounds in vitro and influences biocontrol of Meloidogyne incognita in tomato by Pseudomonas fluorescens strain CHA0 and its GM derivatives.

AIMS: The aim of the present investigation was to determine the influence of Rhizoctonia solani and its pathogenicity factor on the production of nematicidal agent(s) by Pseudomonas fluorescens strain CHA0 and its GM derivatives in vitro and nematode biocontrol potential by bacterial inoculants in tomato. METHODS AND RESULTS: One (Rs7) of the nine R. solani isolates from infected tomato roots inhibited seedling emergence and caused root rot in tomato. Thin layer chromatography revealed that culture filtrates of two isolates (Rs3 and Rs7) produced brown spots at Rf-values closely similar to synthetic phenylacetic acid (PAA), a phytotoxic factor. Filtrates from isolate Rs7, amended with the growth medium of P. fluorescens, markedly repressed nematicidal activity and PhlA'-'LacZ reporter gene expression of the bacteria in vitro. On the contrary, isolate Rs4 enhanced nematicidal potential of a 2,4-diacetylphloroglucinol overproducing mutant, CHA0/pME3424, of P. fluorescens strain CHA0 in vitro. Therefore, R. solani isolates Rs4 and Rs7 were tested more rigorously for their potential to influence biocontrol effectiveness of the bacterial agents. Methanol extract of the culture filtrates of PAA-producing isolate Rs7 resulting from medium amended with phenylalanine enhanced fungal repression of the production of nematicidal agents by bacteria, while amendments with zinc or molybdenum eliminated such fungal repression, thereby restoring bacterial potential to cause nematode mortality in vitro. A pot experiment was carried out, 3-week-old tomato seedlings were infested with R. solani isolates Rs4 or Rs7 and/or inoculated with Meloidogyne incognita, the root-knot nematode. The infested soil was treated with aqueous cell suspensions (10(8) CFU) of P. fluorescens strain CHA0 or its GM derivatives or left untreated (as a control). Observations taken 45 days after nematode inoculation revealed that, irrespective of the bacterial treatments, galling intensity per gram of fresh tomato roots was markedly higher in soil amended with isolate Rs4 than in Rs7-amended soils. Soil amendments with R. solani and the bacterial antagonists resulted in substantial reductions of the number of galls per gram of root. These results are contradictory to those obtained under in vitro conditions where culture filtrates of PAA-positive Rs7 repressed the production of nematicidal compounds. Plants grown in Rs7-amended soils, with or without bacterial inoculants, had lesser shoot and root weights than plants grown in nonamended or Rs4-amended soils. Moreover, amendments with Rs7 substantially retarded root growth and produced necrotic lesions that reduced the number of entry sites for invasion and subsequent infection by nematodes. Populations of P. fluorescens in the tomato rhizosphere were markedly higher in Rs7-amended soils. CONCLUSIONS: PAA-producing virulent R. solani drastically affects the potential of P. fluorescens to cause death of M. incognita juveniles in vitro and influences bacterial effectiveness to suppress nematodes in tomato roots. SIGNIFICANCE AND IMPACT OF THE STUDY: As most agricultural soils are infested with root-infecting fungi, including R. solani, it is likely that some PAA-producing isolates of the fungus may also be isolated from such soils. The inhibitory effect of PAA-producing R. solani on the biosynthesis of nematicidal agent(s) critical in biocontrol may reduce or even eliminate the effectiveness of fluorescent pseudomonads against root-knot nematodes, both in nursery beds and in field conditions. Introduction of bacterial inoculants, for the control of any plant pathogen, should be avoided in soils infested with PAA-producing R. solani. Alternatively, the agents could be applied together with an appropriate quantity of fungicide or chemicals such as zinc to create an environment more favourable for bacterial biocontrol action.

Animals↗
PubMed1999

Strategies of cruciferous pathogenic fungi: detoxification of the phytoalexin cyclobrassinin by mimicry.

The remarkable metabolism of the cruciferous phytoalexin cyclobrassinin by the phytopathogenic root rot (Rhizoctonia solani Kuhn) and blackleg [Phoma lingam (Tode ex Fr.) Desm., asexual stage of Leptosphaeria maculans (Desm.) Ces. et de Not.] fungi is reported. It was established that R. solani metabolized and detoxified cyclobrassinin via the phytoalexin brassicanal A, which was further transformed into nontoxic products. Detoxification of cyclobrassinin in P. lingam avirulent isolate Unity occurred via the phytoalexin brassilexin, whereas the detoxification in P. lingam virulent isolate BJ 125 occurred via the phytoalexin dioxibrassinin. The chemistry involved in the structure determination of the intermediates of these three apparently different pathways and their antifungal activities are described. In addition, efficient syntheses of both phytoalexins brassicanal A and brassilexin by mimicry of the fungal biotransformation route are reported. Implications of these unprecedented transformations are discussed.

Brassicaceae↗
PubMed2005

Infection of Rosellinia necatrix with purified viral particles of a member of Partitiviridae (RnPV1-W8).

Isolate W8 of the white root rot fungus, Rosellinia necatrix, harbors three dsRNA segments, L1-, L2- and M-dsRNAs, and showed an irregular colony margin, slow growth, and moderate virulence. The M-dsRNA was previously shown to be the genome of a partitivirus, RnPV1-W8. Here a transfection protocol was developed for RnPV1-W8. Protoplasts of two virus-free isolates of R. necatrix were inoculated with purified viral particles using a polyethylene glycol-mediated method. Virus infection was confirmed by electrophoresis and Northern analysis. RnPV1-W8 introduced into the new host isolates was transmissible via hyphal anastomosis. However, the infection had no effect on the morphology and virulence of infected isolates of R. necatrix. This is the first report on the transfection of a partitivirus for R. necatrix.

Ascomycota↗
PubMed2006

Pip, a novel activator of phenazine biosynthesis in Pseudomonas chlororaphis PCL1391.

Secondary metabolites are important factors for interactions between bacteria and other organisms. Pseudomonas chlororaphis PCL1391 produces the antifungal secondary metabolite phenazine-1-carboxamide (PCN) that inhibits growth of Fusarium oxysporum f. sp. radius lycopersici the causative agent of tomato foot and root rot. Our previous work unraveled a cascade of genes regulating the PCN biosynthesis operon, phzABCDEFGH. Via a genetic screen, we identify in this study a novel TetR/AcrR regulator, named Pip (phenazine inducing protein), which is essential for PCN biosynthesis. A combination of a phenotypical characterization of a pip mutant, in trans complementation assays of various mutant strains, and electrophoretic mobility shift assays identified Pip as the fifth DNA-binding protein so far involved in regulation of PCN biosynthesis. In this regulatory pathway, Pip is positioned downstream of PsrA (Pseudomonas sigma factor regulator) and the stationary-phase sigma factor RpoS, while it is upstream of the quorum-sensing system PhzI/PhzR. These findings provide further evidence that the path leading to the expression of secondary metabolism gene clusters in Pseudomonas species is highly complex.

Amino Acid Sequence↗
PubMed2003

Biochemical, genetic, and zoosporicidal properties of cyclic lipopeptide surfactants produced by Pseudomonas fluorescens.

Zoospores play an important role in the infection of plant and animal hosts by oomycetes and other zoosporic fungi. In this study, six fluorescent Pseudomonas isolates with zoosporicidal activities were obtained from the wheat rhizosphere. Zoospores of multiple oomycetes, including Pythium species, Albugo candida, and Phytophthora infestans, were rendered immotile within 30 s of exposure to cell suspensions or cell culture supernatants of the six isolates, and subsequent lysis occurred within 60 s. The representative strain SS101, identified as Pseudomonas fluorescens biovar II, reduced the surface tension of water from 73 to 30 mN m-1. The application of cell suspensions of strain SS101 to soil or hyacinth bulbs provided significant protection against root rot caused by Pythium intermedium. Five Tn5 mutants of strain SS101lacked the abilities to reduce the surface tension of water and to cause lysis of zoospores. Genetic characterization of two surfactant-deficient mutants showed that the transposons had integrated into condensation domains of peptide synthetases. A partially purified extract from strain SS101 reduced the surface tension of water to 30 mN m-1 and reached the critical micelle concentration at 25 micrograms ml-1. Reverse-phase high-performance liquid chromatography yielded eight different fractions, five of which had surface activity and caused lysis of zoospores. Mass spectrometry and nuclear magnetic resonance analyses allowed the identification of the main constituent as a cyclic lipopeptide (1,139 Da) containing nine amino acids and a 10-carbon hydroxy fatty acid. The other four zoosporicidal fractions were closely related to the main constituent, with molecular massesranging from 1,111 to 1,169 Da.

Amino Acid Sequence↗
PubMed2006

Genetic population structure of three Armillaria species at the landscape scale: a case study from Swiss Pinus mugo forests.

Armillaria species are plant pathogens that cause Armillaria root rot and are known to cause mortality of mountain pines (Pinus mugo) in the Swiss National Park in the Central Alps. The identity of isolates and the spatially explicit population structure of the Armillaria species were investigated in a 3.3km(2) study area in the Swiss National Park. In total, 242 Armillaria isolates, 205 from wood samples and 37 from epiphytic rhizomorphs, were collected. Species were identified using haploid-diploid pairings and genets were determined using intraspecific somatic incompatibility tests. The population structure differed markedly among the Armillaria species. A. cepistipes and A. borealis mainly occurred as genets of small spatial extent (mean 0.2ha, and 0.6ha), whereas A. ostoyae formed significantly larger genets (mean 6.8ha). The largest A. ostoyae genet extended over approx. 37ha. Several disease centres associated with Heterobasidion annosum were found to be embedded within large Armillaria genets. The extension of large A. ostoyae genets suggests that forests that occupy the study area have developed in the presence of these Armillaria genets. The finding of large Armillaria genets supports the assumption that large genets occur in areas with cold climate and little precipitation.

Agaricales↗
PubMed2006

Rhodanobacter spathiphylli sp. nov., a gammaproteobacterium isolated from the roots of Spathiphyllum plants grown in a compost-amended potting mix.

Three Gram-negative, yellow-pigmented strains were isolated from the rhizospheres of Spathiphyllum plants grown in a compost-amended potting mix. The strains showed biological control activity towards the root-rot plant pathogen Cylindrocladium spathiphylli, and were characterized to determine their taxonomic position. Cells of the strains were non-motile rods, and the strains were oxidase- and catalase-positive and unable to ferment most sugars tested. The three strains showed differences in growth temperature range, optimal growth temperature and some biochemical reactions. The majority of the fatty acids were branched, and large amounts of 15 : 0 iso and 17 : 1 iso omega9c were present. The 16S rRNA gene sequence (1,497 bp) of strain B39(T) showed the highest level of similarity (98.5 %) to that of Rhodanobacter fulvus IAM 15025(T), followed by Rhodanobacter lindaniclasticus LMG 18385(T) (96.0 %; strain no longer extant), Dyella koreensis CCUG 50883(T) (96.4 %), Dyella japonica DSM 16301(T) (96.3 %), Frateuria aurantia LMG 1558(T) (96.2 %) and Fulvimonas soli LMG 19981(T) (95.9 %). Less than 90 % 16S rRNA gene sequence similarity was observed for other members of the Gammaproteobacteria. The mean DNA-DNA reassociation value for the three strains was 100 % and was 25 % when the strains were compared with DNA from R. fulvus LMG 23003(T). The strains had a mean DNA G+C content of 67.6 mol%. On the basis of their phylogenetic, genomic and phenotypic properties, the three strains represent a novel species within the genus Rhodanobacter, for which the name Rhodanobacter spathiphylli sp. nov. is proposed. The type strain is strain B39(T) (=LMG 23181(T)=DSM 17631(T)).

Antibiosis↗
PubMed2006

Changes in communities of Fusarium and arbuscular mycorrhizal fungi as related to different asparagus cultural factors.

Asparagus (Asparagus officinalis) is a high-value perennial vegetable crop that has shown a marked decline in productivity after many years of continuous harvesting. This decline is caused by an increase in both abiotic (autotoxicity, harvesting pressure) and biotic stresses [fungal infections, mainly Fusarium crown and root rot (FCRR)]. To gain insight into disease development and possible mitigation strategies, we studied the effects of harvesting, time in the growing season, and field age on FCRR development, Fusarium species composition, and arbuscular mycorrhizal fungi (AMF) communities in both a controlled field experiment and an ecological survey of commercial fields. In one experiment, a 3-year-old asparagus field was subdivided into plots that were harvested or not and sampled throughout the growing season to assess short-term dominant Fusarium species shifts. In addition, diseased and healthy asparagus plants sampled from six commercial fields in the same geographical region were used to assess Fusarium and AMF communities in relation to different parameters. Fusarium and AMF communities were described by using a polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) approach, and results were analyzed by mainly correspondence analysis and canonical correspondence analysis. Results showed that dominant Fusarium taxa assemblages changed throughout the growing season. Harvested plots had significantly more FCRR symptomatic plants at the end of the growing season, but this effect was not related with any trend in Fusarium community structure. Sampling site and plant age significantly influenced AMF community structure, whereas only sampling site consistently influenced the Fusarium community. Diseased and healthy plants harbored similar Fusarium and AMF communities. Shifts in Fusarium community might not be responsible for different disease incidence because they are ubiquitous regardless of plant health status or harvesting regime. The different incidence noted might rather be related to plant physiology, antagonist microbial communities, or soil parameters.

Asparagus Plant↗
PubMed2000

Effects of carbohydrates, ethanol and selected cell wall phenolics on in vitro growth of necrotrophic fungi--Heterobasidion annosum and Fusarium avenaceum.

In this study, a comparative assessment was undertaken of nutritional factors that are likely to influence in vivo growth of the S and P-types of necrotrophic root rot fungus Heterobasidion annosum and of the damping off pathogen Fusarium avenaceum respectively. The results indicate that glucose and fructose but not cellobiose or sucrose supported growth of these fungi when used as sole carbon source. Particularly for P-types and F. avenaceum, however, the utilization of cellobiose and sucrose was considerably enhanced by several fold in the presence of ethanol. In addition, key plant cell wall phenolics (ferulic acid, caffeic acid, p-coumaric acid) at 0.025% inhibited growth of the test fungi. But this toxicity was reversed in the presence of exogenously added cell wall sugars (glucose, fructose, sucrose, cellobiose) except for the P-types where sucrose addition was apparently slightly effective. Similarly, ethanol whether alone or in combination with the phenolics was poorly utilized except for F. avenaceum. The importance of these results in understanding factors influencing growth and development during pathogenesis of the necrotrophs on their conifer hosts is discussed.

Basidiomycota↗
PubMed2002

PCR Sampling of disease resistance-like sequences from a disease resistance gene cluster in soybean.

Clusters of Resistance-like genes (RLGs) have been identified from a variety of plant species. In soybean, RLG-specific primers and BAC-fingerprinting were used to develop a contig of overlapping BACs for a cluster of RLGs on soybean linkage group J. The resistance genes Rps2 ( Phytophthora stem and root rot) and Rmd-c (powdery mildew) and the ineffective nodulation gene Rj2 were previously mapped to this region of linkage group J. PCR hybridization was used to place two TIR/NBD/LRR cDNAs on overlapping BACs from this contig. Both of the cDNAs were present on BAC 34P7. Fingerprinting of this BAC suggested as many as twelve different RLGs were present. Given the high nucleotide identity shared between cDNAs LM6 and MG13 (>90%), direct sequencing of this region would be difficult. More sequence information was needed about the RLGs within this region before sequencing could be undertaken. By comparing the genomic sequences of cDNAs LM6 and MG13 we identified conserved regions from which oligonucleotide primers specific to BAC 34P7 RLGs could be designed. The nine primer pairs spanned the genomic sequence of LM6 and produced overlapping RLG products upon amplification of BAC 34P7. Amplification products from 12 different RLGs were identified. On average, nucleotide identity between RLG sequences was greater than 95%. Examination of RLG sequences also revealed evidence of additions, deletions and duplications within targeted regions of these genes. Using previously mapped cDNAs we were able to quickly and inexpensively access multiple RLGs within a single specific cluster.

Journal Article↗
PubMed2002

Recessive resistance genes against potyviruses are localized in colinear genomic regions of the tomato ( Lycopersicon spp.) and pepper ( Capsicum spp.) genomes.

Resistance against both Potato virus Y (PVY) and Tobacco etch virus (TEV) was identified in the wild tomato relative Lycopersicon hirsutum PI247087. Analysis of the segregation ratio in F(2)/F(3) and BC(1) interspecific progenies indicated that a single recessive gene, or two very tightly linked recessive loci, are involved in resistance to both potyviruses. This locus was named pot-1. Using amplified fragment length polymorphism markers and a set of L. hirsutum introgression lines, pot-1 was mapped to the short arm of tomato chromosome 3, in the vicinity of the recessive py-1 locus for resistance to corky root rot. Because of the occurrence of phenotypically similar genes in pepper ( Capsicum spp.), the comparative genetics of resistance to potyviruses between tomato and pepper was investigated. Unlike most of the comparative genetic studies on resistance genes, pot-1 was tightly flanked by the same restriction fragment length polymorphism (RFLP) markers than the pvr2/pvr5 locus for resistance to PVY and TEV from pepper. These results may indicate that recessive resistance genes against potyviruses evolve less rapidly than the majority of the dominant genes cloned so far, and consequently may belong to a different family of resistance genes.

Journal Article↗