Four phenotypically and phylogenetically distinct lineages in Phytophthora lateralis

Area of Science:

• Plant Pathology
• Mycology
• Phylogenetics

Background:

• Phytophthora lateralis historically caused dieback and mortality in Lawson cypress (Chamaecyparis lawsoniana) within its native Pacific Northwest (PNW) range.
• Since the 1990s, disease outbreaks have increased on ornamental C. lawsoniana in Europe, and the pathogen was found in Taiwan in 2007, suggesting potential endemicity.

Purpose of the Study:

• To compare phenotypes of over 150 Phytophthora lateralis isolates from Taiwan, the PNW, and Europe.
• To determine the phylogenetic relationships among these geographically diverse isolates.
• To identify and characterize distinct populations of P. lateralis.

Main Methods:

• Phenotypic comparison of isolates based on growth rate, colony patterns, and spore metrics.
• Multivariate analysis to discriminate between subtypes.
• Comparative sequencing of two mitochondrial and three nuclear genes to test phylogenetic assumptions.

Main Results:

• Three main growth rate groups were resolved: slow-growing from Taiwan, fast-growing from the PNW and Europe, and intermediate-growing from the UK.
• Distinct subtypes were identified within growth groups, further discriminated by multivariate analysis.
• Phylogenetic analysis confirmed the distinctness of the three main growth groups and revealed two additional distinct clusters within the Taiwan group, resulting in four unique populations: PNW, UK, Taiwan J, and Taiwan K lineages.

Conclusions:

• Four phenotypically and genotypically unique populations of Phytophthora lateralis (PNW, UK, Taiwan J, Taiwan K lineages) have been identified.
• These lineages exhibit distinct characteristics and geographical distributions.
• The findings have significant implications for understanding the evolution, taxonomy, and plant health risks associated with Phytophthora lateralis.