PCR–RFLP identifies differences in hrpZ sequences to distinguish two genetic groups of Pseudomonas syringae pv. syringae strains from barley and wheat with bacterial black nod

Differences in hrpZ sequences determined by polymerase chain reaction (PCR)–restriction fragment length polymorphism (RFLP) were used to investigate the molecular epidemiology of Pseudomonas syringae pv. syringae (PSS) strains that were isolated from diseased barley and wheat plants in Okayama, Japan. PCR–RFLP using HhaI separated PSS strains into two groups (A and B). Although specific PCR–RFLP groups of PSS strains were not always isolated from specific cultivars or seeds produced in a specific area, many strains isolated from barley and wheat belonged to PCR–RFLP groups A and B, respectively.     

Incidence of ‘Candidatus Liberibacter europaeus’ and phytoplasmas in Cacopsylla species (Hemiptera: Psyllidae) and their host/shelter plants

Psyllids, as vectors of phloem-restricted plant pathogens, are serious agricultural pests. Fruit tree phytoplasmas are transmitted by different Cacopsylla spp., while other psyllids are known vectors of liberibacters. Recently, the bacterium ??Candidatus Liberibacter europaeus?? was found in pear trees and in Cacopsylla pyri (Linnaeus), the vector of ??Ca. Phytoplasma pyri??. This new species does not cause symptoms in plants and is probably a symbiont rather than a pathogen. Based on these findings and the assumption that ??Ca. Liberibacter europaeus?? is widespread, we studied its distribution in the genus Cacopsylla and in the respective host and shelter plants (where psyllids aestivate and overwinter), as well as its possible co-presence with ??Ca. Phytoplasma?? spp. We tested 14 Cacopsylla species and 11 plant species from northwestern Italy, Hungary and Israel, characterized by warm oceanic, temperate continental and warm Mediterranean climatic conditions, respectively. ??Ca. Liberibacter europaeus?? was common within the Cacopsylla genus, being present in nine of the 14 species screened as well as in most host plants, whereas none of the shelter plants tested positive for this bacterium. Altogether, these findings indicate the presence of ??Ca. Liberibacter europaeus?? in continental zones, whereas it does not seem to be widespread in the Mediterranean region. Furthermore, lack of specific symptoms in all infected plants confirms an endophytic relationship with this bacterium, while its abundance in insects suggests a beneficial role for the host. Co-infections with phytoplasmas, observed in insects and plants, require further study to evaluate the possible interactions between them.     

Fruit Exocarp Phenols in Relation to Quiescence and Development of Monilinia fructicola Infections in Prunus spp.: A Role for Cellular Redox?

ABSTRACT Monilinia fructicola causes brown rot of Prunus species and usually remains quiescent on immature fruit but reactivates when fruit are mature. The dihydroxycinnamates caffeic acid and its quinate ester, chlorogenic acid, abundant in the exocarp of peach fruit, had no effect on fungal growth but markedly inhibited the production of the cell wall degrading enzymes polygalacturonase and cutinase in M. fructicola cultures. This inhibition was related to changes in the electrochemical redox potentials of the cultures, as measured with a redox electrode. Fungal culture filtrates had lower electrochemical redox potentials when the growth medium contained caffeic acid than in caffeic acid-free medium. Levels of total intracellular glutathione, the reduced form of which serves as a major cellular antioxidant, increased significantly in M. fructicola cells in response to external caffeic acid. The presence of caffeic acid, chlorogenic acid, or reduced glutathione in conidial suspensions of M. fructicola did not inhibit germination on flower petals and fruit, but inhibited appressorium formation from germinated conidia and subsequent brown rot lesion development. These results suggest that intracellular antioxidant levels in the pathogen can be influenced by phenols present in host tissue and that changes in the redox environment may influence gene expression and differentiation of structures associated with infection by the pathogen. The possible relationship of host phenols to quiescence and subsequent development of M. fructicola infections is discussed.     

Invasion of Phytophthora infestans at the landscape level: how do spatial scale and weather modulate the consequences of spatial heterogeneity in host resistance?

Strategic spatial patterning of crop species and cultivars could make agricultural landscapes less vulnerable to plant disease epidemics, but experimentation to explore effective disease-suppressive landscape designs is problematic. Here, we present a realistic, multiscale, spatiotemporal, integrodifference equation model of potato late blight epidemics to determine the relationship between spatial heterogeneity and disease spread, and determine the effectiveness of mixing resistant and susceptible cultivars at different spatial scales under the influence of weather. The model framework comprised a landscape generator, a potato late blight model that includes host and pathogen life cycles and fungicide management at the field scale, and an atmospheric dispersion model that calculates spore dispersal at the landscape scale. Landscapes consisted of one or two distinct potato-growing regions (6.4-by-6.4-km) embedded within a nonhost matrix. The characteristics of fields and growing regions and the separation distance between two growing regions were investigated for their effects on disease incidence, measured as the proportion of fields with ≥1% severity, after inoculation of a single potato grid cell with a low initial level of disease. The most effective spatial strategies for suppressing disease spread in a region were those that reduced the acreage of potato or increased the proportion of a resistant potato cultivar. Clustering potato cultivation in some parts of a region, either by planting in large fields or clustering small fields, enhanced the spread within such a cluster while it delayed spread from one cluster to another; however, the net effect of clustering was an increase in disease at the landscape scale. The planting of mixtures of a resistant and susceptible cultivar was a consistently effective option for creating potato-growing regions that suppressed disease spread. It was more effective to mix susceptible and resistant cultivars within fields than plant some fields entirely with a susceptible cultivar and other fields with a resistant cultivar, at the same ratio of susceptible to resistant potato plants at the landscape level. Separation distances of at least 16 km were needed to completely prevent epidemic spread from one potato-growing region to another. Effects of spatial placement of resistant and susceptible potato cultivars depended strongly on meteorological conditions, indicating that landscape connectivity for the spread of plant disease depends on the particular coincidence between direction of spread, location of fields, distance between the fields, and survival of the spores depending on the weather. Therefore, in the simulation of (airborne) pathogen invasions, it is important to consider the large variability of atmospheric dispersion conditions.     

Can a specialist parasite species of a widespread and common host species be rare? The case of Spinitectus inermis (Nematoda: Cystidicolidae) in eels Anguilla anguilla

The claim by many authors that Spinitectus inermis (Zeder, 1800), a narrowly specific parasite of European eels Anguilla anguilla (L.), is a rare species is considered at three levels: its geographical range, its frequency of occurrence compared to other eel parasites and its relative abundance in component communities. The parasite is widely distributed in freshwater throughout the European range of the eel but its occurrence is erratic and unpredictable, being known from only 8 countries. Surveys of eel parasites in the United Kingdom and in Continental Europe show that it is present in only 13% of British and 29% of continental localities. This satisfies one of the criteria for rarity. When present, its prevalence ranges from 1.8% to 43.3%, so it can be considered rare in some localities but in a few it may be common and on occasion it may be the dominant species in the gastro-intestinal community. Populations of S. inermis are almost always characterised by high levels of overdispersion, even at low prevalence. The species also displays an ability to colonise a locality following introduction there. Overall it meets many of the criteria of a rare species including a restricted distribution and a low frequency of occurrence and so it can be considered to exhibit diffusive rarity.     

Diversity of microsporidia (Fungi: Microsporidia) among captive great apes in European zoos and African sanctuaries: evidence for zoonotic transmission?

Abstract: Two hundred and seventeen captive great apes (150 chimpanzees, Pan troglodytes; 14 bonobos, Pan paniscus; 53 western gorillas, Gorilla gorilla) and 20 personnel from thirteen European zoos and two African sanctuaries were sampled and examined in order to determine the occurrence ofEnterocytozoon bieneusi and species of Encephalitozoon in faecal specimens and to compare the epidemiological situation between zoos and sanctuaries. Microsporidia were detected at all sampling sites. Sequence analyses of ITS amplicons generated by using microsporidia-specific primers determined the presence ofmicrosporidia in 87 samples including 13 humans; since two cases of simultaneous occurrence of Encephalitozoon cuniculi and Enterocytozoon bieneusi were identified, 89 full-length ITS sequences were obtained, namely 78 Encephalitozoon cuniculi genotype I, five E. cuniculi genotype II, two E. hellem 1A and four Enterocytozoon bieneusi. No Encephalitozoon intestinalis-positive samples were identified. This is the first report of Encephalitozoon species and Enterocytozoon bieneusi genotypes in captive great apes kept under various conditions and the first record of natural infection with E. hellem in great apes. A comparison of zoos and sanctuaries showed a significantly higher prevalence of microsporidia in sanctuaries (P<0.001), raising a question about the factors affecting the occurrence of microsporidia in epidemiologically and sanitarily comparable types of facilities.