Abstract
Fusarium oxysporum is a soilborne fungal plant pathogen responsible for causing disease in many economically important crops with “special forms” (formae speciales) adapted to infect specific plant hosts. F. oxysporum f. sp. pisi (FOP) is the causal agent of Fusarium wilt disease of pea. It has been reported in every country where peas are grown commercially. Disease is generally controlled using resistant cultivars possessing single major gene resistance and therefore there is a constant risk of breakdown. The main aim of this work was to characterise F. oxysporum isolates collected from diseased peas in the United Kingdom as well as FOP isolates obtained from other researchers representing different races through sequencing of a housekeeping gene and the presence of Secreted In Xylem (SIX) genes, which have previously been associated with pathogenicity in other F. oxysporum f. spp. F. oxysporum isolates from diseased United Kingdom pea plants possessed none or just one or two known SIX genes with no consistent pattern of presence/absence, leading to the conclusion that they were foot-rot causing isolates rather than FOP. In contrast, FOP isolates had different complements of SIX genes with all those identified as race 1 containing SIX1, SIX6, SIX7, SIX9, SIX10, SIX11, SIX12, and SIX14. FOP isolates that were identified as belonging to race 2 through testing on differential pea cultivars, contained either SIX1, SIX6, SIX9, SIX13, SIX14 or SIX1, SIX6, SIX13. Significant upregulation of SIX genes was also observed in planta over the early stages of infection by different FOP races in pea roots. Race specific SIX gene profiling may therefore provide potential targets for molecular identification of FOP races but further research is needed to determine whether variation in complement of SIX genes in FOP race 2 isolates results in differences in virulence across a broader set of pea differential cultivars.
Highlights
Fusarium oxysporum is the most widely dispersed and economically important plant pathogenic species in the Fusarium genus as it infects numerous hosts and causes extensive crop losses (Leslie and Summerell, 2006)
Fusarium isolates collected from diseased peas from United Kingdom fields were identified using translation elongation factor 1α (TEF) gene sequencing, with the majority being confirmed as F. oxysporum, in addition to isolates of F. solani and Fusarium redolens
The maximum likelihood phylogenetic tree based on TEF gene sequences, separated the F. oxysporum isolates from United Kingdom peas, FOP isolates and sequences from other f. spp. into a total of eight clades
Summary
Fusarium oxysporum is the most widely dispersed and economically important plant pathogenic species in the Fusarium genus as it infects numerous hosts and causes extensive crop losses (Leslie and Summerell, 2006). Spp.), adapted to infect specific hosts plants. These are thought to have evolved though convergent evolution and many are polyphyletic (Fourie et al, 2011; van Dam et al, 2018); isolates from one f. In F. oxysporum, more than 150 host specific formae speciales have been described (Edel-Hermann and Lecomte, 2019), including well studied and economically important examples such as F. oxysporum f. Lycopersici (FOL), cubense, and pisi are examples of f. Spp. which contain multiple economically damaging races, which are specialised to infect certain cultivars of a host species; for example, f. F. oxysporum f. sp. lycopersici (FOL), cubense, and pisi are examples of f. spp. which contain multiple economically damaging races, which are specialised to infect certain cultivars of a host species; for example, f. sp. cubense tropical race 4 which is devasting the popular Cavendish cultivar of banana in the tropics (Ploetz, 2015)
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