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Genotypic diversity of globally derived isolates of Fusarium oxysporum f. sp. fragariae

Peter Henry: University of California

<div>Fusarium wilt of strawberry (caused by <em>Fusarium oxysporum</em> f. sp. <em>fragariae</em>) was first reported in Australia in 1962 and soon after observed in Japan (1969) and South Korea (1974). New reports of this disease surged globally in the early to mid-2000’s, coinciding with decreased availability of the fumigant methyl bromide. Studies of genetic diversity in national populations have been conducted in Australia, South Korea, and California, but the methods for assessing diversity are not consistent between publications. Therefore, little is known about genetic diversity in the global population, or the extent to which this pathogen may have been trafficked between countries. Corresponding authors from 15 publications reporting <em>F.o. fragariae </em>in 7 countries were contacted for the isolates used in their study. From this query, DNA or cultures were obtained from 27 Australian, 22 Japanese, 18 Korean, 8 Spanish, and 11 Californian isolates (86 total). The translation elongation factor 1a (EF-1a; ~700bp) and nuclear ribosomal intergenic spacer (IGS; ~2.2 kbp) loci were sequenced from all isolates and used to construct multi-locus phylogenetic trees. Each isolate was additionally PCR-tested for presence of a locus that is diagnostic of some <em>F.o. fragariae </em>strains. Thirty-nine isolates representing diverse haplotypes from each country were tested for pathogenicity on cultivars known to be susceptible and resistant to <em>F.o. fragariae</em> in California. Several clades with high bootstrap support included isolates from multiple countries, which suggests international movement may have occurred more than once. The challenges to, and opportunities for, preventing future dispersal are discussed.</div>