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opencc-zeroJan 2021View details →

Neighboring trees regulate the root-associated pathogenic fungi on the host plant in a subtropical forest

Root-associated fungi and host-specific pathogens are major determinants of species coexistence in forests. Phylogenetically related neighboring trees can strongly affect the fungal community structure of the host plant, which, in turn, will affect the ecological processes. Unfortunately, our understanding of the factors influencing fungal community composition in forests is still limited. In particular, investigation of the relationship between the phytopathogenic fungal community and neighboring trees is incomplete. In the current study, we tested the host specificity of members of the root-associated fungal community collected from seven tree species and determined the influence of neighboring trees and habitat variation on the composition of the phytopathogenic fungal community of the focal plant in a subtropical evergreen forest. Using high-throughput sequencing data with respect to the internal transcribed spacer (ITS) region, we characterized the community composition of the root-associated fungi and found significant differences with respect to fungal groups among the seven tree species. The density of conspecific neighboring trees had a significantly positive influence on the relative abundance of phytopathogens, especially host-specific pathogens, while the heterospecific neighbor density had a significant negative impact on the species richness of host-specific pathogens, as well as phytopathogens. Our work provides evidence that the root-associated phytopathogenic fungi of a host plant depends greatly on the tree neighbors of the host plant.

opencc-zeroDec 2010View details →

Data from: Fungal pathogen species richness: why do some plant species have more pathogens than others?

Variation among plant species in the number of associated herbivore and pathogen species is predicted to fit a species-area relationship in which the area or biomass embodied by a plant species is a function of individual size and geographic range size. This hypothesis is tested using published estimates of geographic range, individual size, and species richness of fungal-pathogens for 490 plant species occurring in the United States and controlling for sampling intensity and phylogenetic effects. The number of pathogens found on a plant species increases with the metrics of plant species' area and/or habitat diversity and their effects are similar between gymnosperm and angiosperm lineages. The strength of this pattern across a diverse set of plant lineages suggests that accumulation and persistence of pathogen species on plant species are governed by the same processes among temperate plants.

opencc-zeroDec 2017View details →

Data from: Shifts in diversification rates and host jump frequencies shaped the diversity of host range among Sclerotiniaceae fungal plant pathogens

The range of hosts that a parasite can infect in nature is a trait determined by its own evolutionary history and that of its potential hosts. However, knowledge on host range diversity and evolution at the family level is often lacking. Here, we investigate host range variation and diversification trends within the Sclerotiniaceae, a family of Ascomycete fungi. Using a phylogenetic framework, we associate diversification rates, the frequency of host jump events, and host range variation during the evolution of this family. Variations in diversification rate during the evolution of the Sclerotiniaceae define three major macro-evolutionary regimes with contrasted proportions of species infecting a broad range of hosts. Host-parasite co-phylogenetic analyses pointed towards parasite radiation on distant hosts long after host speciation (host jump or duplication events) as the dominant mode of association with plants in the Sclerotiniaceae. The intermediate macro-evolutionary regime showed a low diversification rate, high frequency of duplication events, and the highest proportion of broad host range species. Our findings suggest that the emergence of broad host range fungal pathogens results largely from host jumps, as previously reported for oomycete parasites, probably combined with low speciation rates. These results have important implications for our understanding of fungal parasites evolution and are of particular relevance for the durable management of disease epidemics.

opencc-zeroDec 2014View details →

Data from: Invasiveness of plant pathogens depends on the spatial scale of host distribution

Plant diseases often cause serious yield losses in agriculture. A pathogen's invasiveness can be quantified by the basic reproductive number, R0. Since pathogen transmission between host plants depends on the spatial separation between them, R0 is strongly influenced by the spatial scale of the host distribution.We present a proof of principle of a novel approach to estimate the basic reproductive number, R0, of plant pathogens as a function of the size of a field planted with crops and its aspect ratio. This general approach is based on a spatially explicit population dynamical model. The basic reproductive number was found to increase with the field size at small field sizes and to saturate to a constant value at large field sizes. It reaches a maximum in square fields and decreases as the field becomes elongated. This pattern appears to be quite general: it holds for dispersal kernels that decrease exponentially or faster, as well as for fat-tailed dispersal kernels that decrease slower than exponential (i.e., power-law kernels).We used this approach to estimate R0 in wheat stripe rust (an important disease caused by Puccinia striiformis), where we inferred both the transmission rates and the dispersal kernels from the measurements of disease gradients. For the two largest datasets, we estimated R0 of P. striiformis in the limit of large fields to be of the order of 30. We found that the spatial extent over which R0 changes strongly is quite fine-scaled (about 30 m of the linear extension of the field). Our results indicate that in order to optimize the spatial scale of deployment of fungicides or host resistances, the adjustments should be made at a fine spatial scale. We also demonstrated how the knowledge of the spatial dependence of R0 can improve recommendations with regard to fungicide treatment.

opencc-zeroDec 2011View details →

Data from: Recent range expansion and agricultural landscape heterogeneity have only minimal effect on the spatial genetic structure of the plant pathogenic fungus Mycosphaerella fijiensis

Understanding how geographical and environmental features affect genetic variation at both the population and individual levels is crucial in biology, especially in the case of pathogens. However, distinguishing between these factors and the effects of historical range expansion on spatial genetic structure remains challenging. In the present study, we investigated the case of Mycosphaerella fijiensis-a plant pathogenic fungus that has recently colonized an agricultural landscape characterized by the presence of potential barriers to gene flow, including several commercial plantations in which disease control practises such as the use of fungicides are applied frequently, and low host density areas. We first genotyped 300 isolates sampled at a global scale on untreated plants in 2 dimensions over a 50x80 Km area. Using two different clustering algorithms, no genetic structure was detected in the studied area, suggesting expansion of large populations and/or no influ ence of potential barriers. Second, we investigated the potential effect of disease control practises on M. fijiensis diversity by comparing populations sampled in commercial vs. food-crop plantations. At this local scale, we detected significantly higher allelic richness inside commercial plantations compared to the surrounding food-crop plantation populations. Analysis of molecular variance (AMOVA) indicated that 99% of the total genetic variance occurred within populations. We discuss the suggestion that high population size and/or high migration rate between populations might be responsible for the absence of any effect of disease control practises on genetic diversity and differentiation.

Data from: The role of habitat filtering in the leaf economics spectrum and plant susceptibility to pathogen infection

The leaf economics spectrum (LES) describes global covariation in the traits of plant leaves. The LES is thought to arise from biophysical constraints and habitat filtering (ecological selection against unfit trait combinations along environmental gradients). However, the role of habitat filtering in generating the LES has not been tested experimentally. If the process of habitat filtering plays a role in generating the LES, the LES could weaken in communities that have yet to be filtered by the current environment, for example after abiotic environmental change. LES traits are commonly used to predict community and ecosystem processes, and if the LES weakens in unfiltered communities, LES-based models may no longer apply. In the glasshouse, we experimentally simulated three stages of habitat filtering in response to abiotic change: from unfiltered, to semi-filtered, to completely filtered communities. In each stage, we quantified the strength of the LES and assessed the accuracy of trait-based models of an important ecological process, pathogen infection. The strength of the LES increased with the completeness of habitat filtering, as did the accuracy of trait-based models of plant susceptibility to pathogen infection. Synthesis. Our results suggest that habitat filtering plays a fundamental role in strengthening the trait correlations of the LES and that trait-based models may be less accurate when communities have not been filtered by the current environment, for example, following rapid environmental change.

opencc-zeroApr 2020View details →

Data from: Landscape simplification shapes pathogen prevalence in plant-pollinator networks

Species interaction networks, which play an important role in determining pathogen transmission and spread in ecological communities, can shift in response to agricultural landscape simplification. However, we know surprisingly little about how landscape simplification-driven changes in network structure impact epidemiological patterns. Here, we combine mathematical modeling and data from eleven bipartite plant-pollinator networks observed along a landscape simplification gradient to elucidate how changes in network structure shape disease dynamics. Our empirical data show that landscape simplification reduces pathogen prevalence in bee communities via increased diet breadth of the dominant species. Furthermore, our empirical data and theoretical model indicate that increased connectance reduces the likelihood of a disease outbreak and decreases variance in prevalence among bee species in the community, resulting in a dilution effect. Because infectious diseases are implicated in pollinator declines worldwide, a better understanding of how land use change impacts species interactions is therefore critical for conserving pollinator health.

Data from: Horizontal gene acquisitions, mobile element proliferation, and genome decay in the host - restricted plant pathogen Erwinia tracheiphila

Modern industrial agriculture depends on high density cultivation of genetically similar crop plants, creating favorable conditions for the emergence of novel pathogens with increased fitness in managed compared to ecologically intact settings. Here, we present the genome sequence of six strains of the cucurbit bacterial wilt pathogen Erwinia tracheiphila (Enterobacteriaceae) isolated from infected squash plants in New York, Pennsylvania, Kentucky, and Michigan. These genomes exhibit a high proportion of recent horizontal gene acquisitions, invasion and remarkable amplification of mobile genetic elements, and pseudogenization of ~20% of the coding sequences. These genome attributes indicate that E. tracheiphila recently emerged as a host-restricted pathogen. Furthermore, chromosomal rearrangements associated with phage and transposable element proliferation contributes to substantial differences in gene content and genetic architecture between the six E. tracheiphila strains and other Erwinia species. Together, these data lead us to hypothesize that E. tracheiphila has undergone recent evolution via both genome decay (pseudogenization) and genome expansion (horizontal gene transfer and mobile element amplification). Despite evidence of dramatic genomic changes, the six strains are genetically monomorphic, suggesting a recent population bottleneck and emergence into E. tracheiphila's current ecological niche.

opencc-zeroDec 2017View details →

Data from: The effects of rainforest fragment area on the strength of plant-pathogen interactions

Pathogenic interactions between fungi and plants facilitate plant species coexistence and tropical rainforest diversity. Such interactions, however, may be affected by forest fragmentation as fungi are susceptible to anthropogenic disturbance. To examine how fragmentation affects fungus-induced seed and seedling mortality, we sowed seeds of six plant species in soils collected from 21 forest fragments. We compared seedling establishment in unmanipulated soils to soils treated with fungicides. Fungicides increased germination of Toona ciliata seeds and decreased mortality of Syzygium rubicundum and Olea dioica seedlings. The fungus-induced mortality of one of these species, S. rubicundum, decreased with decreasing fragment size, indicating that its interactions with pathogenic fungi may weaken as fragments become smaller. We provide evidence that a potential diversity-maintaining plant-fungus interaction weakens in small forest fragments and suggest that such disruptions may have important long-term consequences for plant diversity. We, however, emphasize the need for further research across rainforest plant communities to better understand the future of diversity in fragmented rainforest landscapes.

Data from: Current and projected global distribution of Phytophthora cinnamomi, one of the world's worst plant pathogens

Globally, Phytophthora cinnamomi is listed as one of the 100 worst invasive alien species and active management is required to reduce impact and prevent spread in both horticulture and natural ecosystems. Conversely, there are regions thought to be suitable for the pathogen where no disease is observed. We developed a CLIMEX model for the global distribution of P. cinnamomi based on the pathogen's response to temperature and moisture and by incorporating extensive empirical evidence on the presence and absence of the pathogen. The CLIMEX model captured areas of climatic suitability where P. cinnamomi occurs that is congruent with all available records. The model was validated by the collection of soil samples from asymptomatic vegetation in areas projected to be suitable by the model for which there were few records. DNA was extracted and the presence or absence of P. cinnamomi determined by high throughput sequencing (HTS). While not detected using traditional isolation methods, HTS detected P. cinnamomi at higher elevations in eastern Australia and central Tasmania as projected by the CLIMEX model. Further support for the CLIMEX model was obtained by using the large dataset from southwest Australia where the proportion of positive records in an area is related to the Ecoclimatic Index value for the same area. We provide for the first time a comprehensive global map of the current P. cinnamomi distribution, an improved CLIMEX model of the distribution, and a projection to 2080 of the distribution with predicted climate change. This information provides the basis for more detailed regional scale modelling and supports risk assessment for governments to plan management of this important soil-borne plant pathogen.

opencc-zeroMar 2020View details →

Bacterial community richness shifts the balance between volatile organic compound-mediated microbe-pathogen and microbe-plant interactions

Even though bacteria are important in determining plant growth and health via volatile organic compounds (VOCs), it is unclear how these beneficial effects emerge in multi-species microbiomes. Here we studied this using a model plant-bacteria system, where we manipulated bacterial community richness and composition and determined the subsequent effects on VOC production and VOC-mediated pathogen suppression and plant growth-promotion. We assembled VOC-producing bacterial communities in different richness levels ranging from one to twelve strains using three soil-dwelling bacterial genera (Bacillus, Paenibacillus and Pseudomonas) and investigated how the composition and richness of bacterial community affect the production and functioning of VOCs. We found that VOC production correlated positively with pathogen suppression and plant growth-promotion and that all bacteria produced a diverse set of VOCs. However, while pathogen suppression was maximized at intermediate community richness levels when the relative amount and the number of VOCs were the highest, plant growth-promotion was maximized at low richness levels and was only affected by the relative amount of plant growth-promoting VOCs. The contrasting effects of richness could be explained by differences in the amount and number of produced VOCs and by opposing effects of community productivity and evenness on pathogen suppression and plant-growth promotion along the richness gradient. Together, these results suggest that the number of interacting bacterial species and the structure of the rhizosphere microbiome drive the balance between VOC-mediated microbe-pathogen and microbe-plant interactions potentially affecting plant disease outcomes in natural and agricultural ecosystems.

opencc-zeroDec 2013View details →

Data from: A hyperparasite affects the population dynamics of a wild plant pathogen

Assessing the impact of natural enemies of plant and animal pathogens on their host's population dynamics is needed to determine the role of hyperparasites in affecting disease dynamics, and their potential for use in efficient control strategies of pathogens. Here we focus on the long-term study describing metapopulation dynamics of an obligate pathogen, the powdery mildew (Podosphaera plantaginis) naturally infecting its wild host plant (Plantago lanceolata) in the fragmented landscape of the Åland archipelago (southwest Finland). Regionally, the pathogen persists through a balance of extinctions and colonizations, yet factors affecting extinction rates remain poorly understood. Mycoparasites of the genus Ampelomyces appear as good candidates for testing the role of a hyperparasite, i.e. a parasite of other parasites, in the regulation of their fungal hosts' population dynamics. For this purpose, we first designed a quantitative PCR assay for detection of Ampelomyces spp. in field-collected samples. This newly developed molecular test was then applied to a large-scale sampling within the Åland archipelago, revealing that Ampelomyces is a widespread hyperparasite in this system, with high variability in prevalence among populations. We found that the hyperparasite was more common on leaves where multiple powdery mildew strains coexist, a pattern that may be attributed to differential exposure. Moreover, the prevalence of Ampelomyces at the plant level negatively affected the overwinter survival of its fungal host. We conclude that this hyperparasite may likely impact on its host population dynamics and argue for increased focus on the role of hyperparasites in disease dynamics.

Data from: Adaptation of a plant pathogen to partial host resistance: selection for greater aggressiveness in grapevine downy mildew

An understanding of the evolution of pathogen quantitative traits in response to host selective pressures is essential for the development of durable management strategies for resistant crops. However, we still lack experimental data on the effects of partial host resistance on multiple phenotypic traits (aggressiveness) and evolutionary strategies in pathogens. We performed a cross-inoculation experiment with four grapevine hosts and 103 isolates of grapevine downy mildew (Plasmopara viticola) sampled from susceptible and partially resistant grapevine varieties. We analysed the neutral and adaptive genetic differentiation of five quantitative traits relating to pathogen transmission. Isolates from resistant hosts were more aggressive than isolates from susceptible hosts, as they had a shorter latency period and higher levels of spore production. This pattern of adaptation contrasted with the lack of neutral genetic differentiation, providing evidence for directional selection. No specificity for a particular host variety was detected. Adapted isolates had traits that were advantageous on all resistant varieties. There was no fitness cost associated with this genetic adaptation, but several trade-offs between pathogen traits were observed. These results should improve the accuracy of prediction of fitness trajectories for this biotrophic pathogen, an essential element for the modelling of durable deployment strategies for resistant varieties.

opencc-zeroNov 2023View details →

Effects of herbivory and pathogen infection on plant-pollinator interactions

Plant enemies can indirectly affect pollinators by modifying plant traits, but simultaneous tests of herbivore and pathogen effects are lacking, and the role of floral volatiles has seldom been mechanistically assessed. In this study, we tested for indirect effects of insect herbivores and pathogens on pollinator attraction via altered floral volatile emissions, and its consequences for plant fitness in Brassica rapa. Plants in the field were exposed to either no damage or damage by caterpillars (Mamestra brassicae), aphids (Brevicoryne brassicae), a leaf fungus (Sclerotinia sclerotiorum), or a bacterium (Xanthomonas campestris pv. campestris). We recorded pollinator visits, and measured floral traits (flower number, volatiles) and plant fitness-correlates. We additionally performed a greenhouse experiment with artificial emitters to test for effects of target floral volatiles on pollinator attraction. In the field experiments, plants subjected to herbivory by the aphid B. brassicae (but not the other enemies) exhibited a marked reduction in the emission of two VOCs (nonanal and 2-butyl-1-octanol), experienced lower pollinator visits, and produced seeds of lower quality in terms of seed biomass and germination rate, while flower output itself was not affected. Artificial emitters with reduced amounts of these compounds were less attractive to pollinators under greenhouse conditions. Synthesis: These results provide strong evidence for volatile-mediated indirect interactions between plant enemies and pollinators ultimately impacting plant fitness, and further point at enemy and compound specificity underlying such effects.

opencc-by-4.0Nov 2024View details →

Sequence and functional analyses of native plasmids from plant pathogenic Gammaproteobacteria: comparative genomics, conjugative mobilization and fitness effects

These data tables are part of the Supplementary Material for Chapter I of the thesis titled "Sequence and Functional Analyses of Native Plasmids from Plant-Pathogenic Gammaproteobacteria: Comparative Genomics, Conjugative Mobilization, and Fitness Effects."

FIGURE 1 in Pseudopestalotiopsis gilvanii sp. nov. and Neopestalotiopsis formicarum leaves spot pathogens from guarana plant: a new threat to global tropical hosts

FIGURE 1. Phylogenetic relationship in Pseudopestalotiopsis inferred with concatenated sequences of ITS, tub2 and tef1-α, showing the placement Pseudopestalotiopsis gilvanii. The tree topology was generated by the ML analysis and bootstrap values for maximum parsimony (MP), maximum likelihood (ML), and posterior probability (PP) analyses are presented at the branches (MP/ML/PP). Isolates from this study are highlighted in blue.

FIGURE 4 in Pseudopestalotiopsis gilvanii sp. nov. and Neopestalotiopsis formicarum leaves spot pathogens from guarana plant: a new threat to global tropical hosts

FIGURE 4. Nucleotides differences in the ITS, tef1-α and tub2 sequences of Pseudopestalotiopsis gilvanii and closely related species. Ten nucleotides up and downstream to the nucleotide variation are in light green.

FIGURE 3 in Pseudopestalotiopsis gilvanii sp. nov. and Neopestalotiopsis formicarum leaves spot pathogens from guarana plant: a new threat to global tropical hosts

FIGURE 3. Pseudopestalotiopsis gilvanii (strain INPA 2913), aspects of colonies in PDA (A), aspects of conidia (B) and scanning electron microscopy of conidia (C). Neopestalotiopsis formicarum (strain INPA 2916), aspects of colonies in PDA (D), aspects of conidia (E) and scanning electron microscopy of conidia (F).

FIGURE 2 in Pseudopestalotiopsis gilvanii sp. nov. and Neopestalotiopsis formicarum leaves spot pathogens from guarana plant: a new threat to global tropical hosts

FIGURE 2. Phylogenetic relationship in Neopestalotiopsis inferred with concatenated sequences of ITS, tub2 and tef1- α. The tree topology was generated by the ML analysis and bootstrap values for maximum parsimony (MP), maximum likelihood (ML), and posterior probability (PP) analyses are presented at the branches (MP/ML/PP). Isolates from this study are highlighted in yellow.

FIGURE 6 in Pseudopestalotiopsis gilvanii sp. nov. and Neopestalotiopsis formicarum leaves spot pathogens from guarana plant: a new threat to global tropical hosts

FIGURE 6. Leaf spot symptoms on tropical plants inoculated with Pseudopestalotiopsis gilvanii and Neopestalotiopsis formicarum, under greenhouse conditions. Presence of symptoms noticed on açaí palms (Euterpe oleraceae and E. precatoria), oil palm (Elaeis guineenses). Banana (Musa paradisiaca) displayed symptoms for N. formicarum but not for Ps. gilvanii. Absence of symptoms on rubber trees (Hevea brasiliensis). Uninoculated plants were employed as control.