[Thesis defence] 19 April 2023 - Thibaud Jayet: "Evolution of pathogens against partial resistance in chilli pepper: impact on their multiplication in planta, on their virulence and on host tolerance", INRAE GAFL et PV

Date and place

19 April 2023
13h30
67 allée des Chênes, domaine St Maurice, 84140 Montfavet

Discipline

Evolutionary biology, plant pathology

Laboratory

GAFL and PV

Management

Director: Véronique Lefebvre (DR)
Co-director: Benoît Moury (DR)

Composition of the jury

Eugénie Hébrard (IRD): Rapporteur
François Delmotte (INRAE): Rapporteur
Nathalie Boissot (INRAE): Examiner
Didier Tharreau (CIRAD): Examiner
Véronique Lefebvre (INRAE): Thesis supervisor
Benoît Moury (INRAE): Thesis co-supervisor

Summary of the thesis

Selecting resistant varieties is an effective way of combating the development of plant pathogens, without using pesticides. Partial disease resistance, which is often polygenic in nature, exerts less selection pressure on pathogen populations than total resistance, which is generally monogenic, and therefore has greater potential for sustainability. In addition, tolerance, which reduces the damage inflicted by a pathogen on its host, is an effective means of reducing the economic impact of pathogens. The main objective of this thesis is to study the adaptation of pathogens to varietal resistance. A systematic review of the literature indicated that the statistical interaction between the type of resistance (total vs. partial) and the pathogen group is a key factor in the durability of varietal resistance. Experimental work focused on the evolution of Potato virus Y (PVY) and the oomycete Phytophthora capsici on related pepper lines with contrasting alleles at the QTLs (quantitative trait loci) of resistance. For PVY, populations showing viral accumulation in plantaincreased or decreased, or induced more damage to their host (i.e. virulent) were selected according to the chilli line on which the virus population had evolved. Lower host tolerance was observed for all populations where an increase in virulence was observed, while lower host tolerance was observed for only one population showing an increase in viral accumulation. Increases in viral accumulation in planta were observed specifically in the most resistant pepper line and imposed a low level of genetic drift on the PVY population at the inoculation stage. Mutations that appeared during experimental evolution were associated with changes in virulence and viral accumulation, and their involvement will soon be assessed by reverse genetics using an infectious PVY clone. For P. capsiciAdapted populations were selected on the line possessing only minor-effect resistance QTLs. Conversely, the line possessing a major effect QTL frequently selected populations showing reduced adaptation. The point mutations and insertion/deletion events associated with these phenotypes will be identified later, by sequencing. Thus, the thesis work indicates that the adaptation of pathogens to their host is influenced by (i) the interaction between the type of resistance (total or partial) and the pathogen group, (ii) the allele combinations at the chilli pepper resistance QTLs and (iii) the level of genetic drift imposed by the host on the pathogen population. Experimental developments are therefore recommended in order to deploy the most sustainable varietal resistances and to determine other sustainability factors in order to improve deployment strategies for resistant or tolerant varieties. Key words: Experimental evolution, PVY, Phytophthora capsiciresistance, tolerance, adaptation