Epidemiology, host range, cultivar resistance and management of Allium rust

RHS project team
Dr Matthew Cromey and Dr Rebekah Robinson
Start date
01/06/2015 08:00:00
End date
26/06/2018 12:00:00
Keywords
Puccinia allii, P. porri, Allium spp., host range, cultivar resistance, epidemiology
The problem
Allium rustAllium rust affects a wide range of ornamental and edible Allium species. While it is usually regarded as a single fungal species, it is actually a complex of related types with overlapping host ranges. Because the rust fungus only grows on living tissue, one way to manage the disease is to minimise the ‘green bridge’ that enables the rust to move from green leaves of one host to another. However, there is only limited information on the population structure of Allium rust (for instance, whether ornamental alliums pose a risk to edible alliums and vice versa), making it difficult to develop recommendations to deal with this green bridge.

Ornamental and vegetable Allium cultivars also differ in their susceptibility to rust. While there is the potential to utilise disease resistance as a management strategy for Allium rust, there is currently insufficient understanding of the variation and genetic basis of resistance.     
Approach
Variation in the Allium rust pathogen
This research will provide important base information for the rest of the project (resistance assessment, gene-for-gene interactions, epidemiology) as well as advancing scientific knowledge in an area of horticultural importance. The finding of a strain intermediate between the ‘leek’ and ‘non-leek’ forms (Sansford et al. 2015) demonstrates that there still much to be discovered. We are collecting and storing isolates from as wide a range of Allium spp. as possible to enable us to characterise differences in morphology, host range and carry out a phylogenetic analysis.

Rust resistance of leek and ornamental Allium cultivars
Identification and quantification of resistance (partial or immunity) in cultivars (particularly those in AGM trials). Field assessment of cultivars in the AGM trials and associated experiments in our field research area, along with more detailed characterisation of resistance in selected cultivars.

Physiologic specialisation
If we find evidence of pathotypes with leek-attacking strains of Allium rust, we will examine gene-for-gene interactions (these are common in rust diseases). Indications of this occurring will include where reputedly resistant cultivars have more disease than expected. The research will involve developing a set of differential cultivars, testing with a range of rust cultures and characterising physiologic specialisation.

Epidemiology
In this part of the project, we will investigate sources of inoculum and how they can be minimised. Host range tests will help us understand where inoculum sources are likely to be located and whether the risk of severe rust can be reduced by eliminating nearby sources of inoculum. We will also examine how the environment and planting date influences disease build-up in susceptible and partially resistant cultivars.

Utilising crop diversity to manage disease
Experiments will be done to determine the potential to mix cultivars and species and vary the layout of vegetable and ornamental plantings to disrupt processes of disease spread, thereby minimising disease epidemics.

Integrated disease management
Existing and new information will be used to develop and refine a set of integrated strategies to manage Allium rust in home gardens.
Benefits to gardeners
The project will provide the scientific knowledge required to develop strategies to minimise carryover of Allium rust inoculum from one host to another. Identification and quantification of resistance (partial or immunity) in cultivars (focussing on those in the Award of Garden Merit (AGM) trials) will feed directly into information that can be made available to gardeners.
Further information
RHS advice: Leek rust
References
Sansford C, Beal E, Denton G, Denton J (2015). First report of the rust Puccinia porri on cultivated Allium vineale 'Hair'. New Disease Reports 31, 4.

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