Phylogenetic Analyses of Phytopathogenic Isolates of Verticillium spp.

Abstract

To better understand the genetic relationships between Verticillium dahliae isolates from lettuce and other phytopathogenic Verticillium spp. isolates from various hosts and geographic locations, the complete intergenic spacer (IGS) region of the nuclear ribosomal RNA gene (rDNA) and the β-tubulin gene were amplified and sequenced. The sequences of the complete IGS region and the β-tubulin gene were used alone and in combination to infer genetic relationships among different isolates of Verticillium with the maximum-likelihood distance method. Phylogenetic analyses set sequences into four distinct groups comprising isolates of V. albo-atrum, V. tricorpus, and V. dahliae from cruciferous and noncruciferous hosts. Within the four Verticillium groups, isolates of V. dahliae from cruciferous hosts displayed the closest affinity to V. dahliae from noncruciferous hosts. Isolates of V. dahliae from noncruciferous hosts could be further divided into four subgroups based on sequence similarities within the IGS region. Cross-pathogenicity tests demonstrated that most Verticillium isolates were as virulent on other hosts as on their hosts of origin. A phenogram based on the cross pathogenicity of individual isolates resembled those derived from the IGS and β-tubulin sequence comparisons. On the basis of the data presented, the potential origin of some isolates of V. dahliae pathogenic on lettuce is proposed.

Diversity, Pathogenicity, and Management of Verticillium Species

“…Even though this information existed in the literature, the taxonomic debate relative to the distinctiveness of these two species continued until the late 1970s when V. dahliae was universally accepted as a species separate from V. albo-atrum (53,109). Subsequent phylogenetic studies have clearly identified V. albo-atrum and V. dahliae as distinct taxa (9,13,26,117).…”

“…If such minimal differences consistently separate the long-spored crucifer strains from other Verticillium species across multiple unlinked genes, then a new species (76) considered the new species V. longisporum to be host specific. V. dahliae generally lacks host specificity, although some strains are more aggressive on certain hosts than others (17,117) or classified as distinct pathotypes (87,110). Usually, strains of V. dahliae are considered to be host adapted rather than host specific because strains have the potential to infect a wide range of hosts but often seem to be most aggressive [disease severity on individual hosts (5)] towards hosts from which they originated (42,117,125).…”

Verticillium dahliaeand other pathogenic fungi inCirsium arvensefrom New Zealand pastures: occurrence, pathogenicity and biological control potential

“…The fungus has also been detected in C. arvense in New Zealand by PCR methods ) using primers specifically targeting the V. dahliae b tubulin gene (Atallah et al 2007), or by closest sequence match with V. dahliae following a GenBank BLASTn search (Dodd et al 2010). Recent research has indicted that, while plant pathogenic species of Verticillium can be distinguished by their morphological characters in culture (Goud et al 2003), the phylogenetic relationship among isolates is complicated (Qin et al 2006;Inderbitzin et al 2011). Future studies on Verticillium spp.…”

First report of the presence of Verticillium dahliae VCG1A in Australia

“…Molecular analysis of the samples using the primer pairs derived from microsatellite sequencing (Berbegal et al 2011) revealed two isolates (DAR82592 and DAR82598, Table 1) to be VCG1A, the cotton D pathotype, thought to be exotic to Australia. The two Australian VCG1A isolates, when compared with the reference isolates (Papaioannou et al 2013), aligned in the subregion P. This result prompted analysis using the Carder et al (1994) and Qin et al (2006) methods with both identifying the presumptive VCG1A isolates as D pathotype, thus supporting the initial VCG1A result. The eight isolates were sent to R.M.…”

“…The size of the amplified product distinguished between D and ND strains; 539 and 523 bp respectively. The third method was to amplify the Intergenic spacer (IGS) region using the primers VdIGSF1 and VdIGSR1 (Qin et al 2006). Comparison of the amplicon sequence to known V. dahliae VCG typed reference isolates determined the presumptive VCG of each isolate.…”