Molecular analysis of Japanese isolates of Verticillium dahliae and V. albo-atrum

Development of the molecular methods for rapid detection and differentiation of Fusarium oxysporum and F. oxysporum f. sp. niveum in Taiwan

Fusarium wilt, caused by Fusarium oxysporum (Fo), is one of the most important fungal diseases worldwide. Like other plant pathogens, Fo displays specialized forms in association with its hosts. For example, F. oxysporum f. sp. niveum (Fon) is the damaging pathogen causing Fusarium wilt disease on watermelon, whereas F. oxysporum f. sp. cubense is the pathogen that infects banana. A rapid and reliable pathogen identification or disease diagnosis is essential for the integrated disease management practices in many crops. In this study, two new primer sets, Fon-1/Fon-2 and FnSc-1/FnSc-2, were developed to differentiate Fon and Fo, respectively. The PCR method using the novel primer sets has high sensitivity to detect Fon when the DNA concentration was as low as 0.01 pg or when the conidia number was as few as 5. In comparison with the published primer set, the Fon-1/Fon-2 primer set, derived from the sequence of OP-M12 random primer-amplified fragment, produced a 174 bp DNA fragment, and was more specific to Fon in Taiwan. In addition, with optimized PCR parameters, the molecular method using the Fon-1/Fon-2 primer set could directly detect Fon even when watermelon samples were collected in its early stage of disease development.

Plant pathogenic Verticillium species: how many of them are there?

SUMMARY Two of the currently widely accepted species in the section Nigrescentia of the genus Verticillium are major plant pathogens inducing wilt diseases in a wide range of mainly dicotyledonous hosts. Three species closely related to these two are less important wilt pathogens and soil saprophytes. A sixth species, V. theobromae, causes the cigar end of banana. Molecular and genetic studies have shown that these species represent a complex pool of discrete lineages of varying degrees of relatedness with unknown levels of gene flow between them. Most isolates are haploid, but some are thought to be amphihaploid interspecific hybrids. Until our understanding of this complex is much improved, it seems most appropriate to add only one new species, for wilt isolates primarily associated with potato and producing dark-resting-mycelium in bundles (currently known as V. albo-atrum Grp2). It is suggested that the following be retained: (i) V. dahliae to include all isolates which produce only microsclerotia, (ii) V. albo-atrum to cover the majority of isolates producing only dark-resting-mycelium (and not in bundles), and (iii) V. nigrescens, V. nubilum, V. tricorpus and V. theobromae for the minor wilt pathogens/saprophytes and the non-wilt pathogen.

Design and development of a DNA array for rapid detection and identification of multiple tomato vascular wilt pathogens

Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici, and Verticillium wilt, caused by either Verticillium albo-atrum or Verticillium dahliae, are devastating diseases of tomato (Lycopersicon esculentum) found worldwide. Monitoring is the cornerstone of integrated pest management of any disease. The lack of rapid, accurate, and reliable means by which plant pathogens can be detected and identified is one of the main limitations in integrated disease management. In this paper, we describe the development of a molecular detection system, based on DNA array technology, for rapid and efficient detection of these vascular wilt pathogens. We show the utility of this array for the sensitive detection of these pathogens from complex substrates like soil, plant tissues and irrigation water, and samples that are collected by tomato growers in their greenhouses.

Molecular evidence that Verticillium ablo-atrum Grp 2 isolates are distinct from V. albo-atrum Grp 1 and V. tricorpus

summary Verticillium species-specific primers were used in a polymerase chain reaction to differentiate between Verticillium albo-atrum groups and V. tricorpus. Amplification with species-specific primers identified 21 isolates from the 64 V. albo-atrum isolates tested as Grp2. Genome analysis using RAPDs and restriction fragment length polymorphism (RFLP) of the intergenic (IGS) region of the rDNA showed that V. albo-atrum Grp2 isolate were genetically distinct from either V. albo-atrum Grp1 or V. tricorpus, demonstrating a significant differentiation between these species. The sizes of the amplified IGS fragment were different, with Grp1 isolates having a smaller fragment ( approximately 2.1 kb) than either Grp2 ( approximately 2.3 kb) or V. tricorpus ( approximately 2.7 kb). Based on RAPD analysis, the average similarity coefficients between Grp1 and Grp2 were 35% and 34% between Grp2 and V. tricorpus. Multiple correspondence analysis separated the isolates into three major groups corresponding to Grp1, Grp2 and V. tricorpus. Surprisingly, isolates collected from Pisum sativa were distinct from other Grp1 V. albo-atrum isolates. The observed low levels of genetic similarity, the differences in sizes of IGS fragments, IGS-RFLP profiles and the RAPD patterns point to the possibility of Grp2 isolates comprising a different species of Verticillium than those occupied by either V. albo-atrum Grp1 isolates or V. tricorpus.

Use of ribotyping and random amplified polymorphic DNA to differentiate isolates of Burkholderia andropogonis

AIMS

The aim of this study was to determine the genetic diversity among isolates of Burkholderia andropogonis from various host plant species and geographic locations.

METHODS AND RESULTS

Both random amplified polymorphic DNA (RAPD) and ribotyping analyses were used to assess the diversity of B. andropogonis isolates and compare these results with pathogenicity assays carried out on a number of common hosts of the organism.

CONCLUSIONS

Both RAPD and ribotyping analyses revealed a high level of genetic diversity between isolates of B. andropogonis. Both methods demonstrated a similar clustering of isolates. However, there was no strict correlation between the genetic diversity revealed and the original host, geographic location or pathogenicity of the isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report on the genetic diversity of isolates of B. andropogonis. The great degree of diversity revealed in this study contrasts with the lack of phenotypic diversity within this species.

Molecular Characterization of Vegetative Compatibility Group 4A and 4B Isolates of Verticillium dahliae Associated with Potato Early Dying

Forty isolates of Verticillium dahliae, collected from potato seed tubers and potato plants from various regions in North America and previously assigned to vegetative compatibility groups (VCGs) 4A or 4B, were characterized using molecular markers. The VCG 4A isolates were previously shown to be a highly virulent pathotype of potato and to interact synergistically with the root-lesion nematode Pratylenchus penetrans to cause potato early dying. All but one of the VCG 4A isolates characterized in this study lacked the subspecies-specific repetitive DNA sequence E18 and could be differentiated from the remaining isolates by restriction fragment length polymorphisms (RFLPs) in the nuclear rDNA and Trp1 loci. The E18 RFLP patterns of several VCG 4B isolates from Maine and New York were highly similar to those of VCG 4B isolates previously collected from potato and tomato fields in Ontario. The data presented here suggest that the molecular markers will be useful for the detection and classification of isolates of V. dahliae associated with potato early dying.