Is there a trade-off between host generalism and aggressiveness across pathogen populations? A synthesis of the global potato and tomato blight lesion growth data

Abstract

Phytophthora infestans is among the most destructive of plant diseases. Pathogen populations have varying degrees of host preference among potato and tomato, from no specificity to extreme specialisation. How host specificity impacts fitness among populations is unclear. Comparing the aggressiveness of both population types can shed light on the determinants of host specificity in P. infestans. A trade-off between generalism and quantitative aggressiveness can explain the variation among strains. I assessed the existence of such a trade-off by analysing the global cross-inoculation data on potato and tomato isolates, and tested whether specificity has changed over time. The synthesis included 44 and 34 data points for potato and tomato isolates respectively. Potato isolates overall did not prefer their original host significantly more than tomato isolates. However, tomato isolates became more generalist over the last few decades. High specificity was associated with significantly greater aggressiveness, and strains from potato can generally infect tomato with similar aggressiveness and specificity as in reverse. This synthesis reveals several novel insights on the evolutionary ecology of the blight pathogen, and provides a new way to map and track P. infestans populations. Many unresolved questions on host specificity and aggressiveness remain which are discussed.

Modelling the displacement and coexistence of clonal lineages of Phytophthora infestans through revisiting past outbreaks

“…Strains of the pathogen vary widely in host specificity on potato and tomato, from generalists that have similar lesion growth rates on both hosts to specialists that are only pathogenic on their preferred host. Strains with different degrees of specificities can reside on the two hosts at many locations, while other locations have a single dominant strain on both hosts (Fry et al., 2015; Legard et al., 1995; Wan, 2023). While mathematical models of disease severity based on weather conditions, fungicide application and cultivar selection have been used to accurately predict disease (e.g., LATEBLIGHT for potato late blight; Andrade‐Piedra et al., 2005), and pathogenesis components have been used effectively in mathematical modelling of disease progression (Skelsey et al., 2009, 2010), there are only a few models on the displacement and coexistence of competing genotypes in clonal plant pathogens.…”

“…infestans worldwide. A model that deals with multiple lineages and hosts over time is necessary to investigate the interactions between genotypes of differing qualities (e.g., with varying host specificity and aggressiveness; Wan, 2023). A model that can simulate genotype frequencies based on pathogenicity traits may help identify potentially invasive emergent strains.…”

“…However, both potato and tomato are major hosts of P. infestans worldwide. A model that deals with multiple lineages and hosts over time is necessary to investigate the interactions between genotypes of differing qualities (e.g., with varying host specificity and aggressiveness; Wan, 2023).…”