Aggressiveness and its role in the adaptation of plant pathogens

Abstract

Aggressiveness, the quantitative component of pathogenicity, and its role in the adaptation of plant pathogens are still insufficiently investigated. Using mainly examples of biotrophic and necrotrophic fungal pathogens of cereals and Phytophthora infestans on potato, the empirical knowledge on the nature of aggressiveness components and their evolution in response to host and environment is reviewed. Means of measuring aggressiveness components are considered, as well as the sources of environmental variance in these traits. The adaptive potential of aggressiveness components is evaluated by reviewing evidence for their heritability, as well as for constraints on their evolution, including differential interactions between host and pathogen genotypes and trade-offs between components of pathogenicity. Adaptations of pathogen aggressiveness components to host and environment are analysed, showing that: (i) selection for aggressiveness in pathogen populations can be mediated by climatic parameters; (ii) global population changes or remarkable population structures may be explained by variation in aggressiveness; and (iii) selection for quantitative traits can influence pathogen evolution in agricultural pathosystems and can result in differential adaptation to host cultivars, sometimes leading to erosion of quantitative resistance. Possible links with concepts in evolutionary ecology are suggested.

An Extended Leaf Disc Test for Virulence Assessment in Plasmopara Viticola and Detection of Downy Mildew Resistance in Vitis

“…This Asiatic species has been previously characterized as suppressing sporulation while reacting with strong necrosis [4,33]. Despite this, it has been reported that stronger necrotic reaction correlates to higher susceptibility in crosses of V. vinifera with V. amurensis [14]. This shows that hosts with stronger resistance might block the sporulation of the pathogen without showing necrosis, which was the case for A. japonica in the present study.…”

“…In our previously published system [7], a set of six host genotypes (two North American species, one European and three commercially used cultivars) was developed to achieve an improved assessment of strain diversity of the oomycete. In the present study, we broaden the characterization system by including The development of necrosis on a specific host reveals the presence of resistance genes [12][13][14] and the level of sporulation achieved by a strain is related to its aggressiveness [15]. Conventional evaluation systems used on P. viticola based on the amount of sporangia do not consider the necrotic reaction of the plant [16][17][18] or evaluate it in combination with the sporulation [13,19].…”

“…Thirty-five of the more than sixty known species from the genus Vitis, originate in China and many of these wild grapes have been used for wine production recently due to their desirable characteristics [30], which confirms their potential for breeding with European species. Even though the presence of several resistant loci have been reported on V. amurensis (Rpv8: [14]; Rpv10: [31]; Rpv12: [33]), it has been shown that there is a strong variation of downy mildew resistance between accessions of this species. While some accessions present a high level of resistance to the pathogen [34], other accessions are susceptible to it [30,35].…”

Genetic and aggressiveness variation among Sclerotinia sclerotiorum dry bean isolates from Brazil fields

“…Pathogenicity may be evaluated in many ways such as infection efficiency, latent period, sporulation rate, infectious period or lesion size (PARIUAD et al, 2009). By measuring lesion progress on stems over time, OttoHanson et al (2011) found that S. sclerotiorum isolates collected from dry bean fields in Minnesota were more aggressive than isolates from Nebraska, Michigan and Washington, whereas California isolates were less aggressive than those collected from all other bean production locations.…”

Spatio‐temporal connectivity and host resistance influence evolutionary and epidemiological dynamics of the canola pathogen Leptosphaeria maculans

“…Where trade‐offs exist between infectivity and other traits that affect pathogen fitness (e.g., spore production; Villaréal & Lannou, 2000; Thrall & Burdon, 2003; Pariaud et al., 2009; Peyraud, Cottret, Marmiesse, Gouzy, & Genin, 2016), theory predicts that regular rotation of cultivars carrying different resistance genes will select against pathogens carrying unnecessary infectivity. However, this may at least partly depend on the initial composition of pathogen populations and whether there are gametic disequilibria (Brown, 1994; Brown & Wolfe, 1990; Hovmøller, Munk, & Østergård, 1993; Kolmer, 1993).…”