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

Framing

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 director
Benoît Moury (INRAE): Thesis co-supervisor

Summary of the thesis

Breeding resistant varieties is an effective way to control the development of plant pathogens without using pesticides. Partial disease resistances, often polygenic in nature, exert less selection pressure on pathogen populations than total resistances, usually monogenic in nature, and therefore have a higher potential for sustainability. In addition, tolerance, which reduces the damage inflicted by a pathogen on its host, is an effective means of control to reduce 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 resistance type (full vs. partial) and pathogen group is a key factor for the durability of varietal resistance. Experimental work focused on the evolution of Potato virus Y (PVY) and the oomycete Phytophthora capsici on related chilli lines contrasting for their alleles at QTLs (quantitative trait loci) of resistance. For PVY, populations with viral accumulation in plantaor decreased, or induced more damage to their host (i.e. virulent) were selected according to the chilli line on which the virus population 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 chilli line and imposed a low level of genetic drift to the PVY population at the inoculation stage. Mutations that emerged during the experimental evolution were associated with changes in virulence and viral accumulation and their involvement will be assessed in the near future by reverse genetics using an infectious PVY clone. For P. capsiciIn this case, adapted populations were selected on the line with only minor effect resistance QTLs. Conversely, the line with a major effect QTL frequently selected populations showing declines in adaptation. The point mutations and insertion/deletion events associated with these phenotypes will be identified at a later stage 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 (full or partial) and the pathogen group, (ii) the combinations in alleles at the chilli resistance QTLs and (iii) the level of genetic drift imposed by the host on the pathogen population. Experimental developments are therefore recommended to deploy the most sustainable varietal resistances and to determine other sustainability factors to improve deployment strategies for resistant or tolerant varieties. Key words : Experimental evolution, PVY, Phytophthora capsiciresistance, tolerance, adaptation