Soft Rot Enterobacteriaceae Are Carried by a Large Range of Insect Species in Potato Fields

Abstract

Pathogenic soft rot (SRE) belonging to the genera and cause diseases in potato and numerous other crops. Seed potatoes are the most important source of infection, but how pathogen-free tubers initially become infected remains an enigma. Since the 1920s, insects have been hypothesized to contribute to SRE transmission. To validate this hypothesis and to map the insect species potentially involved in SRE dispersal, we have analyzed the occurrence of SRE in insects recovered from potato fields over a period of 2 years. Twenty-eight yellow sticky traps were set up in 10 potato fields throughout Norway to attract and trap insects. Total DNA recovered from over 2,000 randomly chosen trapped insects was tested for SRE, using a specific quantitative PCR (qPCR) TaqMan assay, and insects that tested positive were identified by DNA barcoding. Although the occurrence of SRE-carrying insects varied, they were found in all the tested fields. While species were dominant among the insects that carried the largest amount of SRE, more than 80 other SRE-carrying insect species were identified, and they had different levels of abundance. Additionally, the occurrence of SRE in three laboratory-reared insect species was analyzed, and this suggested that SRE are natural members of some insect microbiomes, with herbivorous carrying more SRE than the cabbage moth () and carnivorous green lacewing larvae (). In summary, the high proportion, variety, and ubiquity of insects that carried SRE show the need to address this source of the pathogens to reduce the initial infection of seed material. Soft rot are among the most important pathogens of a wide range of vegetables and fruits. The bacteria cause severe rots in the field and in storage, leading to considerable harvest losses. In potato, efforts to understand how soft rot bacteria infect and spread between healthy plants have been made for over a century. Early on, fly larvae were implicated in the transmission of these bacteria. This work aimed at investigating the occurrence of soft rot bacteria in insects present in potato fields and at identifying the species of these insects to better understand the potential of this suspected source of transmission. In all tested potato fields, a large proportion of insects were found to carry soft rot bacteria. This suggests a need to give more weight to the role of insects in soft rot ecology and epidemiology to design more effective pest management strategies that integrate this factor.

Pectobacterium parvum sp. nov., having a Salmonella SPI-1-like Type III secretion system and low virulence

“…Also proteins annotated as chitinase and chitin binding protein were among the identified P. parvum -specific proteins. Soft rot Pectobacteriaceae have been identified in numerous insect species [ 34 ] and in slugs [ 35 ], and they can also be vectored by free living [ 36 ] and root-knot nematodes [ 37 ]. The characteristics of the P. parvum -specific genes may suggest that it forms a more intimate relationship with a vector when compared to P. polaris or other Pectobacteriaceae species.…”

May the Phage be With You? Prophage-Like Elements in the Genomes of Soft Rot Pectobacteriaceae: Pectobacterium spp. and Dickeya spp.

“…Among the economically most important hosts worldwide are potato, carrot, tomato, onion, pineapple, maize, rice, hyacinth, chrysanthemum, and calla lily (Perombelon and Kelman, 1980; Charkowski, 2018). SRP are widespread in various ecological niches including bulk and rhizosphere soils, water, sewage, the surface of host and non-host plants, and the surfaces and interior of insects (Perombelon and Kelman, 1980; Grenier et al, 2006; Rossmann et al, 2018). Because of the diverse habitats in which they can be found, bacteria presumably also exhibit diverse lifestyles because of their transfer between these different environments; for example, from plants to soil, from plant to plant, from host plant to non-host plant, from surface and/or irrigation water to plants, from water to soil, and vice versa ) (Charkowski, 2018).…”

May the phage be with you? Prophage-like elements in the genomes of Soft Rot Pectobacteriaceae (Pectobacterium spp. and Dickeya spp.)

“…SRP are widespread in various ecological niches viz . bulk and rhizosphere soils, water, sewage, on host and non-host plants as well as they are present on and inside insects (Perombelon and Kelman, 1980;Grenier et al, 2006;Rossmann et al, 2018). Likewise, SRP, because of their lifestyle, are often transferred between different environments (for example: from plant to soil, from plant to plant, from surface and/or irrigation water to plant, from water to soil, and vice verse) (Charkowski, 2018).…”