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Aphanomyces (Saprolegniales, Oomycetes) includes some of the most economically and environmentally devastating pathogens of plants and freshwater animals. Despite research focused on its pathogenicity and dispersal, key biological questions, such as host range and specialization, remain poorly understood. In this study, we investigated the host preference and specialization within Aphanomyces . First, we delineated species boundaries employing delimitation algorithms based on 261 representative sequences of the nuclear ribosomal internal transcriber spacer (nrITS) from 261 samples of 20 described species and several unidentified taxa. Our results suggested that Aphanomyces diversity was previously underestimated, since we identified 14 putative new species. Furthermore, we compiled an interaction database of 1221 host records. Network analyses revealed Aphanomyces as a highly specialized group mainly targeting two clusters of hosts: freshwater animals or plants in wet terrestrial soils. In addition, pathogenic Aphanomyces species appeared to be highly specialized. This study represents the first investigation encompassing the full diversity of Aphanomyces species, not only economically relevant species. Our results set the basis to better understand the evolutionary history of host specialization of harmful oomycete pathogens.

Perina nuda (Lepidoptera: Lymantriidae) is a serious pest of banyan trees (Ficus spp.), which is distributed in South China, but little is known about the host preference on the different banyan tree species. To address this gap, we conducted experiments to investigate larval feeding preferences, assessing the impact of feeding experience in both choice and no-choice conditions. Fifth and sixth instars were exposed to 4 banyan species, and food intake, feeding area, and relative ingestion index were measured. Our findings reveal that Ficus concinna was the preferred host of fifth instars in choice tests, while sixth instars exhibited a preference for this host in no-choice tests. In contrast, fifth instars did not display a significant preference for any of the 4 species in no-choice tests. However, sixth instars fed on F. microcarpa, F. altissima, and F. concinna continued to exhibit a preference for the original host. These observations indicate that larval feeding preference changes with instar, and feeding experience contributes to a preference for the original host. Consequently, the feeding preference of P. nuda larvae is influenced by multiple factors, including instar and previous feeding experience. These findings enhance our understanding of P. nuda's ecological interactions and its potential impact on various banyan tree species.

Background Q fever is a zoonotic disease with virtually worldwide dissemination. Its bacterial agent, Coxiella burnetii , is primarily found in cattle and small ruminants. Disease manifestation is highly variable, i.e. asymptomatic, acute or chronic in humans, and subclinical or present as reproductive disorders in ruminants. Different genomic lineages of C. burnetii have been recognized and are considered to show host preferences and influence the disease outcome. The virulence of C. burnetii is essentially determined by effector proteins that modulate host cell processes, allowing the bacterium to persist and proliferate in the host. Thus, these effectors have been suggested to play a role in the presumed host specificity and disease manifestation. Results In the present study, a comprehensive set of 140 C. burnetii genomes from ten Genomic Groups (GGs) and various hosts was studied bioinformatically to determine if there was an association between their genomic characteristics, including the effector protein repertoire, and their isolation source. The differences in genome size, IS1111 count, number of coding sequences, accessory genome and others could be attributed to lineage-specific traits. Likewise, the GGs showed conserved sets of effector proteins, although intra-lineage variances were high in GGIV. Several effector proteins, e.g. Cem8 (CBU_1634a) and CBU_0469, were highly conserved, while CBU_2007 showed a remarkably high number of sequence variants. Conclusions C. burnetii exhibits genomic diversity that aligns with phylotypes rather than host species, suggesting that genomic traits as well as host factors influence disease outcome rather than a host species specific adaptation.

Rhizobial diversity and host preferences were assessed in 65 native Fynbos legumes of the papilionoid legume tribes Astragaleae, Crotalarieae, Genisteae, Indigofereae, Millettieae, Phaseoleae, Podalyrieae, Psoraleeae and Sesbanieae. Sequence analyses of chromosomal 16S rRNA, recA, atpD and symbiosis-related nodA, nifH genes in parallel with immunogold labelling assays identified the symbionts as alpha- (Azorhizobium, Bradyrhizobium, Ensifer, Mesorhizobium and Rhizobium) and beta-rhizobial (Burkholderia) lineages with the majority placed in the genera Mesorhizobium and Burkholderia showing a wide range of host interactions. Despite a degree of symbiotic promiscuity in the tribes Crotalarieae and Indigofereae nodulating with both alpha- and beta-rhizobia, Mesorhizobium symbionts appeared to exhibit a general host preference for the tribe Psoraleeae, whereas Burkholderia prevailed in the Podalyrieae. Although host genotype was the main factor determining rhizobial diversity, ecological factors such as soil acidity and site elevation were positively correlated with genetic variation within Mesorhizobium and Burkholderia, respectively, indicating an interplay of host and environmental factors on the distribution of Fynbos rhizobia. This study is the most comprehensive phylogenetic assessment of rhizobia within the Fynbos biome, showing that legumes are specifically associated with Burkholderia and Mesorhizobium, the latter underestimated within Fynbos soils.

Background Pulses are essential components of agricultural production systems, post-harvest losses caused by storage insect pests remain a major challenge. Callosobruchus maculatus (F.) is a widespread pest of stored legumes, and its host preference is influenced by seed type and associated physico-biochemical traits. This study examined the determinants of C. maculatus preference among nine legume species using controlled laboratory assays and seed trait analyses. Results Under no-choice conditions, chickpea ( Cicer arietinum L), pigeon pea ( Cajanus cajan L.) , and moth bean ( Vigna aconitifolia (Jacq.) Maréchal) supported high oviposition, larval development, and adult emergence, suggesting their overall biological suitability as hosts. In contrast, the common bean ( Phaseolus vulgaris L.) was the most preferred oviposition substrate under free-choice conditions but exhibited poor hatching and emergence, indicating its role as an oviposition trap. Black gram ( Vigna mungo L.) , soybean ( Glycine max (L.) Merr) , and moth bean, though less preferred, supported high post-embryonic success, revealing latent susceptibility. Green gram ( Vigna radiata L. ), black gram, red gram, cowpea ( Vigna unguiculata L. ), and moth bean exhibited high intrinsic suitability, reflected by positive growth indices, shorter developmental durations (notably in black gram and green gram), and balanced oviposition with adult longevity. Conclusion Principal component analysis identified two major axes of host discrimination: (i) physical traits governing oviposition preference and (ii) biochemical composition determining larval development. Seeds with greater surface area, thinner seed coats, and moderate sphericity were favoured for egg deposition, whereas high protein and carbohydrate content enhanced larval growth. In contrast, anti-nutritional factors such as tannins and phytic acid negatively affected larval performance. These findings underscore the significance of integrating physico-biochemical resistance traits into legume breeding and storage management strategies to reduce bruchid-related post-harvest losses.

The fall armyworm (FAW), Spodoptera frugiperda , has emerged as a major global threat to maize production due to its highly invasive nature, absence of diapause, and capacity for continuous reproduction in tropical environments. While off-season irrigated maize is generally recognized as a “green-bridge” for FAW population continuity between seasons, yet its actual contribution relative to alternative hosts remains unclear. To quantify the roles of maize and non-maize hosts in sustaining FAW populations across seasons under climatic continuity and cropping system structures typical of tropical agroecosystems, we assessed FAW seasonal persistence by integrating controlled cage experiments with intensive pest surveys across 123 fields during both irrigated and rain-fed seasons in the Koga Irrigation Scheme, northwestern Ethiopia. Host preference assays revealed that FAW exhibited little host discrimination, feeding readily on finger millet and barley and causing 100% plant mortality, while wheat exhibited 75% severity by 30 days after larval hatching (DAH). Tef sustained significantly slower damage progression (10%, P < 0.001), yet suffered total destruction in the absence of maize. Field survey exhibited near-ubiquitous FAW presence (99.2% prevalence), with 4.3-fold increased FAW incidence and 2.9-fold increased severity ( P < 0.001) during the irrigation season. Structural equation modeling further showed that potato and finger millet exert the strongest positive effects on FAW incidence (β = 0.73 and β = 0.65, respectively; p < 0.001), followed by maize (β = 0.49, p < 0.01). Elevated infestations after crop rotations, combined with the minimal host preference, demonstrated that FAW persists throughout the irrigation season regardless of crop type. This makes off-season irrigated fields a critical “green bridge”, with some alternative hosts contributing better than maize in sustaining FAW populations. Integrating intensified off-season FAW management strategies into a coordinated, landscape-level framework would be essential for lowering population carry-over and mitigating pest pressure sustainably in the subsequent cropping seasons.

Background Chlamydia (C.) psittaci , the causative agent of avian chlamydiosis and human psittacosis, is a genetically heterogeneous species. Its broad host range includes parrots and many other birds, but occasionally also humans (via zoonotic transmission), ruminants, horses, swine and rodents. To assess whether there are genetic markers associated with host tropism we comparatively analyzed whole-genome sequences of 61 C. psittaci strains, 47 of which carrying a 7.6-kbp plasmid. Results Following clean-up, reassembly and polishing of poorly assembled genomes from public databases, phylogenetic analyses using C. psittaci whole-genome sequence alignment revealed four major clades within this species. Clade 1 represents the most recent lineage comprising 40/61 strains and contains 9/10 of the psittacine strains, including type strain 6BC, and 10/13 of human isolates. Strains from different non-psittacine hosts clustered in Clades 2– 4. We found that clade membership correlates with typing schemes based on SNP types, ompA genotypes, multilocus sequence types as well as plasticity zone (PZ) structure and host preference. Genome analysis also revealed that i) sequence variation in the major outer membrane porin MOMP can result in 3D structural changes of immunogenic domains, ii) past host change of Clade 3 and 4 strains could be associated with loss of MAC/perforin in the PZ, rather than the large cytotoxin, iii) the distinct phylogeny of atypical strains (Clades 3 and 4) is also reflected in their repertoire of inclusion proteins (Inc family) and polymorphic membrane proteins (Pmps). Conclusions Our study identified a number of genomic features that can be correlated with the phylogeny and host preference of C. psittaci strains. Our data show that intra-species genomic divergence is associated with past host change and includes deletions in the plasticity zone, structural variations in immunogenic domains and distinct repertoires of virulence factors.

The forest canopy is home to a rich biota. One salient feature are the dynamics of the habitat‐building trees, which are growing and eventually vanishing. Tree species strongly differ in growth rates, final size and longevity. Nevertheless, these inherent dynamics have been a blind spot in studies on host specificity of vascular epiphytes (vascular plants dwelling on trees without parasitizing them)—not least because tree growth rates and longevity are usually unknown in highly diverse tropical forests. The present study aims at tackling this blind spot. We compared epiphyte abundances (>23,000 individuals) found on 285 individuals of four focal tree species in a lowland moist forest in Panama. Data on repeated dbh censuses from a permanent tree plot provided the unique opportunity to estimate the age of our sampled trees. We compared the relative importance of tree longevity for host biases with that of other host tree characteristics, namely microclimatic conditions and bark acidity, rugosity and stability. The studied tree species differ in host quality and epiphyte species partly differ in host preferences. The conclusions concerning relative host tree quality depend hugely on whether or not different tree growth rates are considered. Comparing these conclusions allows important insights into the role of tree longevity in shaping epiphyte communities. Relating tree trait differences to the observed distributions of epiphytes among the focal tree species shows how the simultaneous action of various tree characteristics causes host biases. Synthesis. This study highlights the substantial but, up to now, hidden role of different tree growth rates for host tree specificity of vascular epiphytes. Future investigations need to consider this possibly confounding factor adequately to avoid spurious conclusions. Differences in tree growth rates have been a blind spot in studies on host specificity of vascular epiphytes. We compared epiphyte abundances on four tree species in a lowland moist forest. Host quality ranking depends hugely on whether tree size or age is used as a covariate. Future investigations need to consider different tree growth rates to avoid spurious conclusions.

Through co‐evolutionary adaptation, phytopathogenic fungi have evolved specialised host preference mechanisms to optimise infection efficacy. Fungi of the Valsa genus infect various Rosaceae fruit trees, with Valsa mali exhibiting a marked host preference for apple trees, while Valsa pyri preferentially colonises pear trees. The divergent secondary metabolite biosynthetic gene clusters (SMBGCs) between these two species may serve as key determinants of their distinct host preferences. In this study, VmPKS5, a polyketide synthase, was identified as a key factor influencing the host preference of V. mali, which is the main pathogen of apple Valsa canker (AVC). Deletion of VmPKS5 greatly reduced the virulence of V. mali in apple trees, but not in pear trees. Deletion of VmPKS5 completely abolished the production of the toxin p‐coumaric acid ethyl ester (p‐CAEE). Exogenous p‐CAEE application partly restored the virulence of ΔVmPKS5 and enhanced the virulence of the wild‐type strain of V. mali. Crucially, heterologous expression of VmPKS5 in V. pyri increased its virulence towards apple trees by production of p‐CAEE during infection. Notably, V. mali can uptake double‐stranded RNA (dsRNA), and exogenous spray of VmPKS5‐dsRNA significantly inhibited the infection by V. mali. This study provides new perspectives on host preference mechanisms of fungal pathogens and green disease control of tree disease by dsRNA fungicides. VmPKS5 mediates the virulence and host preference of Valsa mali by regulating the synthesis of p‐coumaric acid ethyl ester (p‐CAEE). Meanwhile, exogenous application of VmPKS5‐dsRNA significantly suppresses the infection caused by V. mali.

Influences of soil environment and willow host species on ectomycorrhizal fungi communities was studied across an hydrologic gradient in temperate North America. Soil moisture, organic matter and pH strongly predicted changes in fungal community composition. In contrast, increased fungal richness strongly correlated with higher plant-available phosphorus. The 93 willow trees sampled for ectomycorrhizal fungi included seven willow species. Host identity did not influence fungal richness or community composition, nor was there strong evidence of willow host preference for fungal species. Network analysis suggests that these mutualist interaction networks are not significantly nested or modular. Across a strong environmental gradient, fungal abiotic niche determined the fungal species available to associate with host plants within a habitat. Soil moisture, pH and organic matter alter the ectomycorrhizal fungal species present in communities regardless of host plant identity. Graphical Abstract Figure. Soil moisture, pH and organic matter alter the ectomycorrhizal fungal species present in communities regardless of host plant identity.