Revisiting the Concept of Host Range of Plant Pathogens

Abstract

Strategies to manage plant disease—from use of resistant varieties to crop rotation, elimination of reservoirs, landscape planning, surveillance, quarantine, risk modeling, and anticipation of disease emergences—all rely on knowledge of pathogen host range. However, awareness of the multitude of factors that influence the outcome of plant–microorganism interactions, the spatial and temporal dynamics of these factors, and the diversity of any given pathogen makes it increasingly challenging to define simple, all-purpose rules to circumscribe the host range of a pathogen. For bacteria, fungi, oomycetes, and viruses, we illustrate that host range is often an overlapping continuum—more so than the separation of discrete pathotypes—and that host jumps are common. By setting the mechanisms of plant–pathogen interactions into the scales of contemporary land use and Earth history, we propose a framework to assess the frontiers of host range for practical applications and research on pathogen evolution.

Host Range Evolution of Potyviruses: A Global Phylogenetic Analysis

“…Molecular determinants of host jumps are largely unknown for plant viruses (but see [3] and references therein), in contrast with molecular determinants involved in the breakdown of resistance genes, i.e., host adaptation at the within-plant-species level. Perhaps the most striking result of this study is the large number of repeated correlated host gains in the potyvirus phylogenetic tree, i.e., the fact that several host gains were inferred on the same branch of the tree.…”

“…For Avena sativa, P 64 was above the 0.35 threshold (0.36), but the status of next branch in the tree was inferred with more confidence (P 65 = 0.24) allowing reliable host change reconstruction. 3 The p value indicates the frequency of random permutations of host and non-host data among the potyvirus species providing a probability that the plant species was host of the potyvirus MRCA lower than the inferred one (P 64 in column 4). 4 Number of changes among potyviruses (i.e., excluding rymoviruses).…”

“…The number and diversity of host species are frequently used to measure a parasites' host range. Host range is an important notion in parasitology, since it is linked to risks of disease emergence [1] and has important consequences on the implementation and efficiency of disease control strategies including epidemiological surveillance, quarantine measures, vaccination, and deployment of parasite-resistant crop varieties in agricultural landscapes [2][3][4].…”

Geometry and evolution of the ecological niche in plant-associated microbes

“…Evidence for different types of cophylogenetic dynamics in plant-fungus symbioses ranging from close congruence indicating codivergence to incongruence indicating long-range host switching ( 36 ). Host jumps (acquisition of a host phylogenetically distant from current hosts) and transitions from specialist to generalist or vice-versa are known in plant pathogens ( 37, 38 ), suggesting that a host range evolution could be more evolutionarily labile than temperature physiology. We found a statistically significant cophylogenetic association between the topologies of three Phytophthora phylogenies and the phylogeny of their plant hosts (436 species-level pathogen-host interaction records; Bayesian phylogeny, m 2 XY = 0.952, p < 0.001; Maximum likelihood phylogeny: m 2 XY = 0.951, p < 0.001; Maximum Parsimony phylogeny: m 2 XY = 0.946, p < 0.001) (Fig.…”

Distinctive Gene Expression Profiles and Effectors Consistent With Host Specificity in Two Formae Speciales of Marssonina brunnea

“…Gathered evidences suggest that gene expression profiles and virulent factors like effectors could be associated with pathogenic host specificity (Parkinson et al, 2016;Poloni and Schirawski, 2016;Inoue et al, 2017;Palma-Guerrero et al, 2017). However, the determinant mechanism underlying host specificity is still waiting to be elucidated (Borah et al, 2018;Frantzeskakis et al, 2019;Morris and Moury, 2019). Yet most of such knowledge at present has been obtained through documents on strains or formae speciales of pathogens against phylogenetically distant hosts (Borah et al, 2018;Frantzeskakis et al, 2019;Morris and Moury, 2019).…”