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11120019 Durability of PCN resistance

Publication Date: 
1 May 2019
Author/Contact :
Author/Contact: 
Kyriakos Varypatakis (PhD student) and John Jones

Contractor :
Contractor: 
The James Hutton Institute

Full Title: Identification of avirulence genes in Globodera pallida as tools for assessing durability of resistance
Duration: October 2015 to September 2018

Background

Plants have a multi-layered immune system to protect themselves from attack by pathogens and pests such as PCN. In turn, the pathogens and pests may be able to circumvent a plant’s first layer of defence by producing proteins (effectors) that supress the plant’s responses. However, a second layer of plant defences involving molecules encoded by resistance genes can recognise the effectors, triggering a strong resistance response (a hypersensitive reaction). Some pests have modified versions of the effector proteins and evade the recognition/hypersensitive response normally conferred by resistance genes. A better understanding of the diversity of effectors in PCN (Globodera pallida), and which effectors are recognised by resistant varieties, will help us predict how durable G. pallida resistance might be. If the effector(s) which trigger a resistance response are highly conserved (little variation in the sequence of amino acids that make up the protein) then it is less likely that resistance will breakdown but if there is substantial variation in the effectors produced by G. pallida, it is considered to be more likely that nematodes with modified versions of effectors that evade the recognition/hypersensitive response will evolve in response to repeated exposure to resistant plants.

The aims of this PhD studentship project were to examine the diversity in effector sequences from G. pallida in order to provide information on the potential durability of resistance. It involved studies of the variation in the virulence of G. pallida i.e. whether different lines of the pest multiply to different extents on a range of potato cultivars.

The student studied the virulence of lines of G. pallida selected on potato cultivars containing various resistance sources in order to determine the potential for selection of virulent G. pallida.

He used capture enrichment sequencing of effector-encoding genes of G. pallida from avirulent and virulent populations of nematodes in order to identify potential candidate avirulence genes. He collaborated on the development of a system for functional testing of candidate avirulence genes.

The outputs and conclusions from the work are that:

  • Virulence against the most commercially widely used resistance sources can be selected if G. pallida is repeatedly exposed to these resistance sources
  • This increased virulence is specific against the resistance source used for selection rather than representing a shift in general aggressiveness of PCN
  • Combining a range of different resistance sources in a single cultivar will therefore provide more durable resistance that will be extremely difficult for PCN to overcome
  • A new genome assembly for Globodera pallida has been generated that shows greatly improved metrics compared to the published sequence
  • Candidate avirulence genes for H3 and S. vernei resistance sources have been identified for functional testing
  • A system for functional testing of candidate avirulence genes has been developed

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