A high-throughput analysis of high-resolution x-ray CT images of stems of olive and citrus plants resistant and susceptible to Xylella fastidiosa

Abstract

The bacterial plant pathogen Xylella fastidiosa causes disease in several globally important crops. However, some cultivars harbour reduced bacterial loads, and express few symptoms. Evidence considering plant species in isolation suggests xylem structure influences cultivar susceptibility to X. fastidiosa. We test this theory more broadly by analysing high-resolution synchrotron X-ray Computed Tomography of healthy and infected plant vasculature from two taxonomic groups containing susceptible and resistant varieties; two Citrus (sweet orange cv. Pera, tangor cv. Murcott), and two olive cultivars (Koroneiki, Leccino). Results found the susceptible plants had more vessels than resistant ones, which could promote within-host pathogen spread. However, features associated with resistance were not shared by citrus and olives. Whilst xylem vessels in resistant citrus stems had comparable diameters to those in susceptible plants, resistant olives had narrower vessels that could limit biofilm spread. And while differences among olive cultivars were not detected, results suggest greater vascular connectivity in resistant vs susceptible citrus plants. We hypothesise this provides alternate flow paths for sustaining hydraulic functionality under infection. In summary, this work elucidates different physiological resistance mechanisms between two taxonomic groups, whilst supporting the existence of an inter-taxonomical metric that could speed up the identification of candidate resistant plants.

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Identifiers

ORCID for Nancy C. Walker: orcid.org/0000-0003-2297-1046

ORCID for Daniel McKay Fletcher: orcid.org/0000-0001-6569-2931

ORCID for Tiina Roose: orcid.org/0000-0001-8710-1063

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