Fitness costs associated with unnecessary virulence factors and life history traits: evolutionary insights from the potato late blight pathogen Phytophthora infestans.
BACKGROUND
In gene-for-gene models of plant-pathogen interactions, the existence of fitness costs associated with unnecessary virulence factors still represents an issue, both in evolutionary biology and agricultural sciences. Measuring such costs experimentally has proven difficult, especially in pathogens not readily amenable to genetic transformation, since the creation of isogenic lines differing only by the presence or absence of avirulence genes cannot be achieved in many organisms. Here, we circumvented this difficulty by comparing fitness traits in groups of Phytophthora infestans isolates sharing the same multilocus fingerprint, but differing by their virulence/avirulence spectrum.


RESULTS
Fitness was assessed from calculations derived from the basic reproduction number, combining several life history traits (latent period, spore density and lesion growth rate) evaluated on leaflets of the potato cultivar Bintje, which is free of resistance genes. A statistically significant fitness cost was found in isolates virulent to the R10 resistance gene. That cost was due to a lower spore production in virulent isolates; however, the latent period was shorter in virulent isolates. Similar trends, although not statistically significant, were observed for the other genes tested.


CONCLUSIONS
The data likely reflect the adaptive response of the pathogen to the cost associated with virulence. They suggest strong trade-offs between life history traits related to pathogenicity and adaptive biology of pathogens.
Montarry
Josselin
J
INRA, Agrocampus-Ouest, UMR1099 BiO3P, Biology of Organisms and Populations applied to Plant Protection, F-35653 Le Rheu, France. josselin.montarry@avignon.inra.fr
Hamelin
Frédéric M
FM
Glais
Isabelle
I
Corbi
Roselyneère
R
Andrivon
Didier
D
D005075:Biological Evolution; D005838:Genotype; D055750:Phytophthora infestans / Q000235:genetics* / Q000378:metabolism*; D010935:Plant Diseases / Q000382:microbiology*; D011198:Solanum tuberosum / Q000382:microbiology*; D014774:Virulence / Q000235:genetics; D037521:Virulence Factors / Q000502:physiology*
D037521:Virulence Factors