The hard life of Phytophthora infestans: when trade‐offs shape evolution in a biotrophic plant pathogen

Abstract

The strict dependency of biotrophic pathogens upon living host tissue for multiplication and survival makes them particularly exposed to evolutionary trade-offs. Such trade-offs can occur both between life history traits directly involved in pathogenicity (e.g. fitness costs due to unnecessary virulence factors), or between traits involved in either pathogenicity (within-season fitness) or survival (between-season fitness). Both types of trade-offs should result in the limitation of maximum pathogenicity, and shape the invasive potential of pathogen genotypes. While strong theoretical developments have been made on evolutionary consequences, including recent work taking seasonality into account (i.e. periodic host absence and/or periodic sexual/asexual reproduction), experimental evidence to confirm theoretical predictions is still scarce. This paper will therefore attempt to illustrate the different kinds of trade-offs that can be measured, and their likely consequences, taking Phytophthora infestans (the cause of potato and tomato late blight) as a case study.

Phenotypic and genotypic changes in French populations of Phytophthora infestans: are invasive clones the most aggressive?

“…As the selection of highly aggressive isolates within the epidemic season has been previously demonstrated (Andrivon et al ., ; Gisi et al ., ), it can be supposed that these aggressive isolates do not bridge epidemic seasons well. This trade‐off hypothesis (Andrivon et al ., ), consistent with the concept of fitness (involving the abilities to both reproduce and survive; Antonovics & Alexander, ), would explain why the highly aggressive clones were not selected during the years of the present study. In West Europe, P. infestans is mainly transmitted asexually between seasons, through volunteer or seed tubers (Johnson, ).…”

Durable Resistance of Crops to Disease: A Darwinian Perspective

“…Synergistic costs of virulence have been detected in Xanthomonas axonopodis pv. vesicatoria (149) and P. infestans (4,97), and it may be especially costly for Puccinia graminis f.sp. tritici to be virulent to certain combinations of Sr genes (50).…”

“…Estimating costs of virulence is usually more challenging than in these examples on at least three accounts: the availability of suitable biological material, integration of epidemiological variables into a single estimate of the cost, and variation in costs between different environments. Furthermore, to get useful predictions about durable resistance, estimates of costs must be relevant to field situations (4,82). Methods of measuring costs of virulence efficiently, reliably, and realistically would make a valuable contribution to breeding for durable resistance.…”

“…There has been considerable interest in using RES genes that detect AVR proteins that are important effectors and thus incur a fitness cost in virulent pathogens that lack them (b > 0) (4,82,85,136,141). This is in accord with a view that durable resistance is any type of resistance to which a parasite cannot readily adapt.…”

“…Third, it may simply be a matter of chance, resulting from a recent population bottleneck. In any case, if a virulence is rare, that does not imply that it is necessarily costly; the cost of virulence must be measured experimentally (4,82,85,141).…”