Clonal expansion and migration of a highly virulent, defoliating lineage of Verticillium dahliae

Michael G. Milgroom, María Del Mar Jiménez-Gasco, Concepción Olivares-García, Rafael M. Jiménez-Díaz

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

We used a population genomics approach to test the hypothesis of clonal expansion of a highly fit genotype in populations of Verticillium dahliae. This fungal pathogen has a broad host range and can be dispersed in contaminated seed or other plant material. It has a highly clonal population structure, with several lineages having nearly worldwide distributions in agricultural crops. Isolates in lineage 1A are highly virulent and cause defoliation in cotton, okra, and olive (denoted 1A/D), whereas those in other lineages cause wilting but not defoliation (ND). We tested whether the highly virulent lineage 1A/D could have spread from the southwestern United States to the Mediterranean basin, as predicted from historical records. We found 187 single-nucleotide polymorphisms (SNPs), determined by genotyping by sequencing, among 91 isolates of lineage 1A/D and 5 isolates in the closely related lineage 1B/ND. Neighbor-joining and maximum-likelihood analyses on the 187 SNPs showed a clear divergence between 1A/D and 1B/ND haplotypes. Data for only 77 SNPs were obtained for all 96 isolates (no missing data); lineages 1A/D and 1B/ND differed by 27 of these 77 SNPs, confirming a clear divergence between the two lineages. No evidence of recombination was detected within or between these two lineages. Phylogenetic and genealogical analyses resulted in five distinct subclades of 1A/D isolates that correlated closely with geographic origins in the Mediterranean basin, consistent with the hypothesis that the D pathotype was introduced at least five times in independent founder events into this region from a relatively diverse source population. The inferred ancestral haplotype was found in two isolates sampled before 1983 from the southwestern United States, which is consistent with historical records that 1A/D originated in North America. The five subclades coalesce with the ancestral haplotype at the same time, consistent with a hypothesis of rapid population expansion in the source population during the emergence of 1A/D as a severe pathogen of cotton in the United States.

Original languageEnglish (US)
Pages (from-to)1038-1046
Number of pages9
JournalPHYTOPATHOLOGY
Volume106
Issue number9
DOIs
StatePublished - Sep 2016

Fingerprint

Verticillium dahliae
defoliation
single nucleotide polymorphism
haplotypes
Southwestern United States
cotton
basins
okra
pathogens
pathotypes
wilting
host range
provenance
genotyping
population structure
genotype
phylogeny
crops
seeds
testing

All Science Journal Classification (ASJC) codes

  • Agronomy and Crop Science
  • Plant Science

Cite this

Milgroom, Michael G. ; Jiménez-Gasco, María Del Mar ; Olivares-García, Concepción ; Jiménez-Díaz, Rafael M. / Clonal expansion and migration of a highly virulent, defoliating lineage of Verticillium dahliae. In: PHYTOPATHOLOGY. 2016 ; Vol. 106, No. 9. pp. 1038-1046.
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Clonal expansion and migration of a highly virulent, defoliating lineage of Verticillium dahliae. / Milgroom, Michael G.; Jiménez-Gasco, María Del Mar; Olivares-García, Concepción; Jiménez-Díaz, Rafael M.

In: PHYTOPATHOLOGY, Vol. 106, No. 9, 09.2016, p. 1038-1046.

Research output: Contribution to journalArticle

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AU - Milgroom, Michael G.

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AB - We used a population genomics approach to test the hypothesis of clonal expansion of a highly fit genotype in populations of Verticillium dahliae. This fungal pathogen has a broad host range and can be dispersed in contaminated seed or other plant material. It has a highly clonal population structure, with several lineages having nearly worldwide distributions in agricultural crops. Isolates in lineage 1A are highly virulent and cause defoliation in cotton, okra, and olive (denoted 1A/D), whereas those in other lineages cause wilting but not defoliation (ND). We tested whether the highly virulent lineage 1A/D could have spread from the southwestern United States to the Mediterranean basin, as predicted from historical records. We found 187 single-nucleotide polymorphisms (SNPs), determined by genotyping by sequencing, among 91 isolates of lineage 1A/D and 5 isolates in the closely related lineage 1B/ND. Neighbor-joining and maximum-likelihood analyses on the 187 SNPs showed a clear divergence between 1A/D and 1B/ND haplotypes. Data for only 77 SNPs were obtained for all 96 isolates (no missing data); lineages 1A/D and 1B/ND differed by 27 of these 77 SNPs, confirming a clear divergence between the two lineages. No evidence of recombination was detected within or between these two lineages. Phylogenetic and genealogical analyses resulted in five distinct subclades of 1A/D isolates that correlated closely with geographic origins in the Mediterranean basin, consistent with the hypothesis that the D pathotype was introduced at least five times in independent founder events into this region from a relatively diverse source population. The inferred ancestral haplotype was found in two isolates sampled before 1983 from the southwestern United States, which is consistent with historical records that 1A/D originated in North America. The five subclades coalesce with the ancestral haplotype at the same time, consistent with a hypothesis of rapid population expansion in the source population during the emergence of 1A/D as a severe pathogen of cotton in the United States.

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