Phytopathogenic, morphological, genetic and molecular characterization of a Verticillium dahliae population from Crete, Greece

A population of 84 V. dahliae isolates mainly originating from Crete, Greece, was characterized in terms of pathogenicity and virulence on different hosts, in parallel with morphological/physiological characterization, vegetative compatibility grouping and mating type determination. Tomato race 2 was found to have supplanted race 1 and was more virulent on a tomato-susceptible cultivar than race 1. Using a differential host classification system which tests pathogenicity to tomato, eggplant, sweet pepper and turnip, 59 isolates were assigned to tomato, 19 to eggplant, one to sweet pepper and five to tomato-sweet pepper pathogenicity groups. All isolates from Crete fell into VCG subgroups 2A, 2B and 4B, while a remarkably high incidence of bridging isolates (compatible with two or more VCGs) was recorded. The tomato-sweet pepper pathogenicity group was morphologically quite distinct from the others, while conidial length and pigment intensity were discriminatory parameters among VCGs 2A, 2B and 4B. PCR-based molecular marker Tr1/Tr2 was reliable in race prediction among tomato-pathogenic isolates, except for members of VCG 4B, while the application of markers Tm5/Tm7 and 35-1/35-2 was highly successful for tomato-pathogenic isolates. E10 marker was related to VCG 2B, rather than to pathogenicity groups. A single nucleotide polymorphism in the ITS2 region, and two novel molecular markers, M1 and M2, proved useful for the fast and accurate determination of major VCGs 2A, 2B and 4B, and can be used for high-throughput population analyses in future studies. The mating type was unrelated to VCG classification and probably does not control heterokaryon incompatibility in V. dahliae. © 2013 KNPV

A robust identification and detection assay to discriminate the cucumber pathogens Fusarium oxysporum f. sp. cucumerinum and f. sp. radicis-cucumerinum

The fungal species Fusarium oxysporum is a ubiquitous inhabitant of soils worldwide that includes pathogenic as well as non-pathogenic or even beneficial strains. Pathogenic strains are characterized by a high degree of host specificity and strains that infect the same host range are organized in so-called formae speciales. Strains for which no host plant has been identified are believed to be non-pathogenic strains. Therefore, identification below the species level is highly desired. However, the genetic basis of host specificity and virulence in F. oxysporum is so far unknown. In this study, a robust random-amplified polymorphic DNA (RAPD) marker-based assay was developed to specifically detect and identify the economically important cucumber pathogens F. oxysporum f. sp. cucumerinum and F. oxysporum f. sp. radicis-cucumerinum. While the F. oxysporum radicis-cucumerinum strains were found to cluster in a separate clade based on elongation factor-1¿ phylogeny, strains belonging to F. oxysporum f. sp. cucumerinum were found to be genetically more diverse. This is reflected in the observation that specificity testing of the identified markers using a broad collection of F. oxysporum strains with all known vegetative compatibility groups of the target formae speciales, as well as representative strains belonging to other formae speciales, resulted in two cross-reactions for the F. oxysporum f. sp. cucumerimum marker. However, no cross-reactions were observed for the F. oxysporum f. sp. radicis-cucumerimum marker. This F. oxysporum f. sp. radicis-cucumerimum marker shows homology to Folyt1, a transposable element identified in the tomato pathogen F. oxysporum f. sp. lycopersici and may possibly play a role in host-range specificity in the target forma specialis. The markers were implemented in a DNA array that enabled parallel and sensitive detection and identification of the pathogens in complex samples from diverse origins