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Entomopathogenicity to Two Hemipteran Insects Is Common but Variable across Epiphytic Pseudomonas syringae Strains.

ABSTRACT: Strains of the well-studied plant pathogen Pseudomonas syringae show large differences in their ability to colonize plants epiphytically and to inflict damage to hosts. Additionally, P. syringae can infect some sap-sucking insects and at least one P. syringae strain is highly virulent to insects, causing death to most individuals within as few as 4 days and growing to high population densities within insect hosts. The likelihood of agricultural pest insects coming into contact with transient populations of P. syringae while feeding on plants is high, yet the ecological implications of these interactions are currently not well understood as virulence has not been tested across a wide range of strains. To investigate virulence differences across strains we exposed the sweet potato whitefly, Bemisia tabaci, and the pea aphid, Acyrthosiphon pisum, both of which are cosmopolitan agricultural pests, to 12 P. syringae strains. We used oral inoculations with bacteria suspended in artificial diet in order to assay virulence while controlling for other variables such as differences in epiphytic growth ability. Generally, patterns of pathogenicity remain consistent across the two species of hemipteran insects, with bacterial strains from phylogroup II, or genomospecies 1, causing the highest rate of mortality with up to 86% of individuals dead after 72 h post infection. The rate of mortality is highly variable across strains, some significantly different from negative control treatments and others showing no discernable difference. Interestingly, one of the most pathogenic strains to both aphids and whiteflies (Cit7) is thought to be non-pathogenic on plants. We also found Cit7 to establish the highest epiphytic population after 48 h on fava beans. Between the nine P. syringae strains tested for epiphytic ability there is also much variation, but epiphytic ability was positively correlated with pathogenicity to insects, suggesting that the two traits may be linked and that strains likely to be found on plants may often be entomopathogenic. Our study highlights that there may be a use for epiphytic bacteria in the biological control of insect crop pests. It also suggests that interactions with epiphytic bacteria could be evolutionary and ecological drivers for hemipteran insects.

SUBMITTER: Smee MR

PROVIDER: S-EPMC5742162 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Entomopathogenicity to Two Hemipteran Insects Is Common but Variable across Epiphytic Pseudomonas syringae Strains.

Smee Melanie R MR Baltrus David A DA Hendry Tory A TA

Frontiers in plant science 20171219

Strains of the well-studied plant pathogen Pseudomonas syringae show large differences in their ability to colonize plants epiphytically and to inflict damage to hosts. Additionally, P. syringae can infect some sap-sucking insects and at least one P. syringae strain is highly virulent to insects, causing death to most individuals within as few as 4 days and growing to high population densities within insect hosts. The likelihood of agricultural pest insects coming into conta ...[more]

PMID: 29312398

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Project description:Interactions between epiphytic bacteria and herbivorous insects are ubiquitous on plants, but little is known about their ecological implications. Aphids are devastating crop pests worldwide, so understanding how epiphytic bacteria impact aphid populations is critically important. Recent evidence demonstrates that plant-associated bacteria, such as Pseudomonas syringae, can be highly virulent to one species of aphid, the pea aphid (Acyrthosiphon pisum). Currently, we have no knowledge on how broad this phenomenon is across diverse aphid species that are of high agricultural concern. In controlled experiments using oral exposure in an artificial diet, we challenged five aphid species of agricultural importance with three strains of P. syringae that vary in virulence to the pea aphid. These strains also vary in epiphytic ability and comprise two phytopathogens and one non-plant-pathogenic strain. In general, differences in virulence to aphids remained relatively constant across strains regardless of the aphid species, except for the bird cherry-oat aphid (Rhopalosiphum padi), which is significantly less susceptible to two P. syringae strains. We demonstrate that lower infection incidence likely plays a role in the reduced susceptibility. Importantly, these data support previous results showing that interactions with epiphytic bacteria are important for aphids and may play a large, but underappreciated, role in insect population dynamics. Our study illustrates a potential role of epiphytic bacteria in the biological control of aphid pests broadly but suggests the need for more research encompassing a greater diversity of pest species.IMPORTANCE Sap-sucking aphids are insects of huge agricultural concern, not only because of direct damage caused by feeding but also because of their ability to transmit various plant pathogens. Some bacteria that grow on leaf surfaces, such as Pseudomonas syringae, can infect and kill aphids, making them potentially useful in the biological control of pest aphids. However, only one aphid species, the pea aphid (Acyrthosiphon pisum), has been tested for infection by P. syringae Here, we challenged five aphid species of agricultural importance with three strains of P. syringae that vary in virulence to the pea aphid. We found that four of these aphid species were susceptible to infection and death, suggesting that these bacteria are broadly useful for biological control. However, one aphid species was much more resistant to infection, indicating that more testing on diverse aphid species is needed.

Project description:The genome sequence of more than 100 Pseudomonas syringae strains has been sequenced to date; however only few of them have been fully assembled, including P. syringae pv. syringae B728a. Different strains of pv. syringae cause different diseases and have different host specificities; so, UMAF0158 is a P. syringae pv. syringae strain related to B728a but instead of being a bean pathogen it causes apical necrosis of mango trees, and the two strains belong to different phylotypes of pv.syringae and clades of P. syringae. In this study we report the complete sequence and annotation of P. syringae pv. syringae UMAF0158 chromosome and plasmid pPSS158. A comparative analysis with the available sequenced genomes of other 25 P. syringae strains, both closed (the reference genomes DC3000, 1448A and B728a) and draft genomes was performed. The 5.8 Mb UMAF0158 chromosome has 59.3% GC content and comprises 5017 predicted protein-coding genes. Bioinformatics analysis revealed the presence of genes potentially implicated in the virulence and epiphytic fitness of this strain. We identified several genetic features, which are absent in B728a, that may explain the ability of UMAF0158 to colonize and infect mango trees: the mangotoxin biosynthetic operon mbo, a gene cluster for cellulose production, two different type III and two type VI secretion systems, and a particular T3SS effector repertoire. A mutant strain defective in the rhizobial-like T3SS Rhc showed no differences compared to wild-type during its interaction with host and non-host plants and worms. Here we report the first complete sequence of the chromosome of a pv. syringae strain pathogenic to a woody plant host. Our data also shed light on the genetic factors that possibly determine the pathogenic and epiphytic lifestyle of UMAF0158. This work provides the basis for further analysis on specific mechanisms that enable this strain to infect woody plants and for the functional analysis of host specificity in the P. syringae complex.

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Entomopathogenicity to Two Hemipteran Insects Is Common but Variable across Epiphytic Pseudomonas syringae Strains.

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Entomopathogenicity to Two Hemipteran Insects Is Common but Variable across Epiphytic <i>Pseudomonas syringae</i> Strains.

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