Elevated CO2 reduces disease incidence and severity of a red maple fungal pathogen via changes in host physiology and leaf chemistry

Atmospheric CO₂ concentrations are predicted to double within the next century. Despite this trend, the extent and mechanisms through which elevated CO₂ affects plant diseases remain uncertain. In this study, we assessed how elevated CO₂ affects a foliar fungal pathogen, Phyllosticta minima, of Acer rubrum growing in the understory at the Duke Forest free‐air CO₂ enrichment experiment in Durham, North Carolina. Surveys of A. rubrum saplings in the 6th, 7th, and 8th years of the CO₂ exposure revealed that elevated CO₂ significantly reduced disease incidence, with 22%, 27%, and 8% fewer saplings and 14%, 4%, and 5% fewer leaves infected per plant in the three consecutive years, respectively. Elevated CO₂ also significantly reduced disease severity in infected plants in all years (e.g. mean lesion area reduced 35%, 50%, and 10% in 2002, 2003, and 2004, respectively). To assess the mechanisms underlying these changes, we combined leaf structural, physiological and chemical analyses with growth chamber studies of P. minima growth and host infection. In vitro exponential growth rates of P. minima were enhanced by 17% under elevated CO₂, discounting the possibility that disease reductions were because of direct negative effects of elevated CO₂ on fungal performance. Scanning electron micrographs (SEM) verified that conidia germ tubes of P. minima infect A. rubrum leaves by entering through the stomata. While stomatal size and density were unchanged, stomatal conductance was reduced by 21–36% under elevated CO₂, providing smaller openings for infecting germ tubes. Reduced disease severity under elevated CO₂ was likely due to altered leaf chemistry and reduced nutritive quality; elevated CO₂ reduced leaf N by 20% and increased the C : N ratio by 20%, total phenolics by 15%, and tannins by 14% (P<0.05 for each factor). The potential dual mechanism we describe here of reduced stomatal opening and altered leaf chemistry that results in reduced disease incidence and severity under elevated CO₂ may be prevalent in many plant pathosystems where the pathogen targets the stomata.     

Effects of host plant environment and Ustilago maydis infection on the fungal endophyte community of maize (Zea mays)

The focus of many fungal endophyte studies has been how plants benefit from endophyte infection. Few studies have investigated the role of the host plant as an environment in shaping endophyte community diversity and composition. The effects that different attributes of the host plant, that is, host genetic variation, host variation in resistance to the fungal pathogen Ustilago maydis and U. maydis infection, have on the fungal endophyte communities in maize (Zea mays) was examined. The internal transcribed spacer (ITS) region of the rDNA was sequenced to identify fungi and the endophyte communities were compared in six maize lines that varied in their resistance to U. maydis. It was found that host genetic variation, as determined by maize line, had significant effects on species richness, while the interactions between line and U. maydis infection and line and field plot had significant effects on endophyte community composition. However, the effects of maize line were not dependent on whether lines were resistant or susceptible to U. maydis. Almost 3000 clones obtained from 58 plants were sequenced to characterize the maize endophyte community. These results suggest that the endophyte community is shaped by complex interactions and factors, such as inoculum pool and microclimate, may be important.     

Genetic variation in eastern North American and putatively introduced populations of Ceratocystis fimbriata f. platani

The plant pathogenic fungus Ceratocystis fimbriata f. platani attacks Platanus species (London plane, oriental plane and American sycamore) and has killed tens of thousands of plantation trees and street trees in the eastern United States, southern Europe and Modesto, California. Nuclear and mitochondrial DNA fingerprints and alleles of eight polymorphic microsatellite markers of isolates of C. fimbriata from these regions delineated major differences in gene diversities. The 33 isolates from the eastern United States had a moderate degree of gene diversity, and unique genotypes were found at each of seven collection sites. Fingerprints of 27 isolates from 21 collection sites in southern Europe were identical with each other; microsatellite markers were monomorphic within the European population, except that three isolates differed at one locus each, due perhaps to recent mutations. The genetic variability of C. fimbriata f. platani in the eastern United States suggests that the fungus is indigenous to this region. The genetic homogeneity of the fungus in Europe suggests that this population has gone through a recent genetic bottleneck, perhaps from the introduction of a single genotype. This supports the hypothesis that the pathogen was introduced to Europe through Naples, Italy during World War II on infected crating material from the eastern United States. The Californian population may also have resulted from introduction of one or a few related genotypes because it, too, had a single nuclear and mitochondrial genotype and limited variation in microsatellite alleles.     

Cryptosphaeria Canker of Populus nigra Caused by Cryptosphaeria pullmanensis,a New Threat to Poplar Industry in Iran

Trunk diseases are potential threats to the poplar industry worldwide, including Iran. A survey on trunk diseases of Populus nigra in north‐western Iran revealed a new canker disease associated with dieback and decline of this host in West Azarbaijan Province of Iran. Wood samples were collected from poplar trees showing canker, dieback and decline symptoms and taken to the laboratory. A total of 173 fungal isolates were recovered from symptomatic tissues, of those 147 isolates had similar cultural and morphological features on potato dextrose agar. Based on a combination of morphological characteristics and phylogenetic inferences including DNA sequence data from the internal transcribed spacer regions (ITS1, 5.8S rDNA, and ITS2), all 147 isolates were identified as Cryptosphaeria pullmanensis. The remaining 26 isolates were identified as Cytospora chrysosperma. Pathogenicity of Cr. pullmanensis on two‐year‐old P. nigra and Populus alba saplings under glasshouse conditions confirmed that Cr. pullmanensis is pathogenic on P. nigra and P. alba. Cryptosphaeria pullmanensis is here reported from Iran causing Cryptosphaeria canker on poplar trees for the first time. However, its host range, the extent of geographical distribution and management strategies remain to be examined.     

Natural selection on floral traits of Lobelia (Lobeliaceae): spatial and temporal variation

The strength and direction of natural selection on floral traits can vary spatially and temporally because of variation in the biotic and abiotic environment. High spatial variation in selection should lead to differentiation of floral traits among populations. In contrast, high temporal variation in selection should retard the evolution of population-specific floral phenotypes. To determine the relative importance of spatial vs. temporal variation in natural selection, we measured phenotypic selection on seven floral traits of the wildflowers Lobelia cardinalis and L. siphilitica in 1999 and 2000. Lobelia cardinalis experienced significant temporal variation in selection, whereas L. siphilitica experienced spatial variation in selection on the same traits. This variation in selection on floral traits was associated with spatial and temporal differences in the soil microenvironment. Although few studies of natural selection include spatial or temporal replicates, our results suggest that such replication is critical for understanding the distribution of phenotypes in nature.     

Epidemiology of onychomycosis and paronychia in the area of ANCONA (ITALY) over a period of 5 years

We retrospectively evaluated the epidemiology of onychomycosis and/or paronychia in 172 patients attending the Clinic of Dermatology and Venereology over a 5 year period. Although yeast isolates, belonging to the Candida species, represented the most frequent etiologic agents of these infections, an increasing prevalence of fungal infections due to emerging fungal pathogens (EFP) was noted throughout this time period. In particular, EFP as causative agents of these infections increased from 0 to 28.4% from 1998 to 2002.     

Canker on culm of Bambusa multiplex (Lour.) Raeusch. ex Schult. caused by Fusarium incarnatum (Roberge) Sacc.

Bambusa multiplex has been broadly cultivated in China and has significant economical, ecological and ornamental importance. A canker on the culm of B. multiplex was first time discovered in 2015 in Shanghai, China. In this study, the fungal isolate XSZ‐1 isolated from the infected tissues was determined to be a pathogen of canker on the culm of B. multiplex by fulfilling Koch's postulates. The fungal pathogen was identified as Fusarium incarnatum based on the morphological characteristics and phylogenetic analyses with the sequences of ITS, TEF‐1α and RPB2. To our knowledge, this is the first report of a canker on the culm of B. multiplex caused by F. incarnatum worldwide.     

Geographic and taxonomic variation in Batrachochytrium dendrobatidis infection and transmission within a highly endemic amphibian community

Aim

In a highly endemic, threatened amphibian assemblage, we measure and describe the geographic and taxonomic distribution of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), with a view to identifying those sites and species most at risk of infection and its negative consequences. Additionally, we aimed to determine the potential for direct transmission events between two known carriers of Bd infection.

Location

The island of Sardinia.

Methods

We collected swab and tissue samples of amphibians from a wide range of geographic sites and species. We used epidemiological and statistical techniques to quantify deviations from a random distribution. We used random forests to investigate habitat use and overlap in two species known to be infected by Bd to quantify a surrogate measure of the contact rates between these two species.

Results

Both geographic and taxonomic distributions of Bd were highly non‐random: we identified a cluster of infections in the north of the island and found that two species, Euproctus platycephalus and Discoglossus sardus, had a relatively high prevalence of infection within this cluster. Our analyses suggest that, on the basis of their fine‐scale habitat use, they have relatively little opportunity for direct transmission and could maintain Bd infection independently.

Main conclusions

Our results illustrate how obtaining detailed information on the geographic and taxonomic distribution of infection is a useful first step in assessing the risk of infection for species within the region. Attempting to quantify possible routes of transmission amongst species further aids us in identifying mechanisms of pathogen persistence within the host community. Within this assemblage, we have identified two hosts that carry infection and may be at risk. Further, our research suggests that these two species may be able to maintain infection independently of one another, which has implications for attempts to mitigate this parasite.

     

Elevated atmospheric carbon dioxide and ozone alter soybean diseases at SoyFACE

Human driven changes in the Earth's atmospheric composition are likely to alter plant disease in the future. We evaluated the effects of elevated carbon dioxide (CO₂) and ozone (O₃) on three economically important soybean diseases (downy mildew, Septoria brown spot and sudden death syndrome‐SDS) under natural field conditions at the soybean free air concentration enrichment (SoyFACE) facility. Disease incidence and/or severity were quantified from 2005 to 2007 using visual surveys and digital image analysis, and changes were related to microclimatic variability and to structural and chemical changes in soybean host plants. Changes in atmospheric composition altered disease expression, but responses of the three pathosystems varied considerably. Elevated CO₂ alone or in combination with O₃ significantly reduced downy mildew disease severity (measured as area under the disease progress curve‐AUDPC) by 39–66% across the 3 years of the study. In contrast, elevated CO₂ alone or in combination with O₃ significantly increased brown spot severity in all 3 years, but the increase was small in magnitude. When brown spot severity was assessed in relation to differences in canopy height induced by the atmospheric treatments, disease severity increased under combined elevated CO₂ and O₃ treatment in only one of the 3 years. The atmospheric treatments had no effect on the incidence of SDS or brown spot throughout the study. Higher precipitation during the 2006 growing season was associated with increased AUDPC severity across all treatments by 2.7 and 1.4 times for downy mildew and brown spot, respectively, compared with drought conditions in 2005. In the 2 years with similar precipitation, the higher daily temperatures in the late spring of 2007 were associated with increased severity of downy mildew and brown spot. Elevated CO₂ and O₃ induced changes in the soybean canopy density and leaf age likely contributed to the disease expression modifications.     

Within-population variation in prevalence and lineage distribution of avian malaria in blue tits, Cyanistes caeruleus

The development of molecular genetic screening techniques for avian blood parasites has revealed many novel aspects of their ecology, including greatly elevated diversity and complex host-parasite relationships. Many previous studies of malaria in birds have treated single study populations as spatially homogeneous with respect to the likelihood of transmission of malaria to hosts, and we have very little idea whether any spatial heterogeneity influences different malaria lineages similarly. Here, we report an analysis of variation in the prevalence and cytochrome b lineage distribution of avian malaria infection with respect to environmental and host factors, and their interactions, in a single blue tit (Cyanistes caeruleus) population. Of 11 Plasmodium and Haemoproteus cytochrome b lineages found in 997 breeding individuals, the three most numerous (pSGS1, pTURDUS1 and pBT7) were considered separately, in addition to analyses of all avian malaria lineages pooled. Our analyses revealed marked spatial differences in the prevalence and distribution of these lineages, with local prevalence of malaria within the population ranging from over 60% to less than 10%. In addition, we found several more complex patterns of prevalence with respect to local landscape features, host state, parasite genotype, and their interactions. We discuss the implications of such heterogeneity in parasite infection at a local scale for the study of the ecology and evolution of infectious diseases in natural populations. The increased resolution afforded by the combination of molecular genetic and geographical information systems (GIS) tools has the potential to provide many insights into the epidemiology, evolution and ecology of these parasites in the future.     

Seasonal variation in Plasmodium prevalence in a population of blue tits Cyanistes caeruleus

1. Seasonal variation in environmental conditions is ubiquitous and can affect the spread of infectious diseases. Understanding seasonal patterns of disease incidence can help to identify mechanisms, such as the demography of hosts and vectors, which influence parasite transmission dynamics. 2. We examined seasonal variation in Plasmodium infection in a blue tit Cyanistes caeruleus population over 3 years using sensitive molecular diagnostic techniques, in light of Beaudoin et al.'s (1971; Journal of Wildlife Diseases, 7, 5-13) model of seasonal variation in avian malaria prevalence in temperate areas. This model predicts a within-year bimodal pattern of spring and autumn peaks with a winter absence of infection. 3. Avian malaria infections were mostly Plasmodium (24.4%) with occasional Haemoproteus infections (0.8%). Statistical nonlinear smoothing techniques applied to longitudinal presence/absence data revealed marked temporal variation in Plasmodium prevalence, which apparently showed a within-year bimodal pattern similar to Beaudoin et al.'s model. However, of the two Plasmodium morphospecies accounting for most infections, only the seasonal pattern of Plasmodium circumflexum supported Beaudoin et al.'s model. On closer examination there was also considerable age structure in infection: Beaudoin et al.'s seasonal pattern was observed only in first year and not older birds. Plasmodium relictum prevalence was less seasonally variable. 4. For these two Plasmodium morphospecies, we reject Beaudoin et al.'s model as it does not survive closer scrutiny of the complexities of seasonal variation among Plasmodium morphospecies and host age classes. Studies of host-parasite interactions should consider seasonal variation whenever possible. We discuss the ecological and evolutionary implications of seasonal variation in disease prevalence.     

Spatial and temporal variation in the diet of a predaceous stonefly (Plecoptera: Perlodidae)

SUMMARY. 1. Spatial and temporal variation in the diet of the univoltine predatory stonefly, Kogotus nonus , was studied over 3 years in a small Alberta stream to determine whether the relative abundance of prey types in the diet of Kogotus reflected relative prey densities in the stream and whether the variation in absolute feeding rate was related to either prey or predator density.
2. The seasonal shift from sole utilization of Orthocladiinae to inclusion of Baetis in the diet could not be attributed to seasonal changes in prey density, but was probably related to predator size and ability to handle very active prey. Most of the spatial variation in diet could be related to differences in background prey densities, but very high densities of Baetis caused the predator to specialize on this prey.
3. Feeding rate on Baetis . as assessed by per capita gut contents, showed a seasonal shift from a positive correlation with Baetis density in winter to a negative relationship with predator density in spring. This suggested that feeding by small Kogotus is a function of prey density. while feeding by later instars is influenced by between predator interactions such as interference.     

Rangewide variation of the maritime pine bast scale matsucoccus feytaudi duc. (Homoptera: matsucoccidae) in relation to the genetic structure of its host

The bast scale Matsucoccus feytaudi is a specific pest of maritime pine, but the damage inflicted by the insect on the host trees is variable, ranging from no apparent effect to severe decline of the maritime pine stands. Rangewide variation of mitochondrial DNA among M. feytaudi populations was analysed by polymerase chain reaction-restriction fragment length-single-strand conformation polymorphism (PCR-RFLP-SSCP) analysis and the results compared with the genetic information already available for its host. Three main nonoverlapping lineages can be distinguished in M. feytaudi. The phylogeography of the pest population is clearly related to the history of its host. Most local associations could result from common evolution while others must be interpreted as intraspecific host shifts. Because the distribution of cultivated tree species is greatly influenced by humans, much may be learned concerning their genetic structure from the indirect study of their specific pests.     

Epizootics and behavioral alteration in the arctiid caterpillar Chionarctia nivea (Lepidoptera: Arctiidae) caused by an entomopathogenic fungus, Entomophaga aulicae (Zygomycetes: Entomophthorales)

We observed epizootics and behavioral alteration in the arctiid caterpillar Chionarctia nivea after infection by an entomopathogenic fungus, Entomophaga aulicae, in April at a riverbank in Kyoto Prefecture, central Japan. The density of arctiid cadavers infected with E. aulicae was 1.31 individuals/m². The critically ill caterpillars crawled up the dead stems of grasses and herbs such as the common reed Phragmites communis and the Japanese mugwort Artemisia indica var. maximowiczii to die at and near the highest parts of the stems, while the healthy larvae usually wandered on the ground and fed on the leaves of small herbs. This behavioral difference could be caused by infection with E. aulicae to enhance dispersal of conidia by active discharge in Entomophthorales with the aid of wind and rainfall.     

First Report of Calonectria ilicicola Causing a New Disease on Laurus (Laurus nobilis) in Europe

Crown and root rot has been detected on potted Laurus nobilis plants in a nursery located in the Catania province (Italy). Perithecia referable to a Calonectria species were consistently detected on crowns and stems of symptomatic plants. Based on morphology, cultural features and molecular analysis, the species was identified as Calonectria ilicicola. Koch’s postulates were fulfilled by pathogenicity tests carried out on potted Laurus nobilis seedlings. To our knowledge, this is the first report of the occurrence of a disease caused by Ca. ilicicola on Laurus nobilis.