Identification of novel aphid‐killing bacteria to protect plants

Abstract

Aphids, including the peach-potato aphid, Myzus persicae, are major insect pests of agriculture and horticulture, and aphid control measures are limited. There is therefore an urgent need to develop alternative and more sustainable means of control. Recent studies have shown that environmental microbes have varying abilities to kill insects. We screened a range of environmental bacteria isolates for their abilities to kill target aphid species. Tests demonstrated the killing aptitude of these bacteria against six aphid genera (including Myzus persicae). No single bacterial strain was identified that was consistently toxic to insecticide-resistant aphid clones than susceptible clones, suggesting resistance to chemicals is not strongly correlated with bacterial challenge. Pseudomonas fluorescens PpR24 proved the most toxic to almost all aphid clones whilst exhibiting the ability to survive for over three weeks on three plant species at populations of 5-6 log CFU cm À2 leaf. Application of PpR24 to plants immediately prior to introducing aphids onto the plants led to a 68%, 57% and 69% reduction in aphid populations, after 21 days, on Capsicum annuum, Arabidopsis thaliana and Beta vulgaris respectively. Together, these findings provide new insights into aphid susceptibility to bacterial infection with the aim of utilizing bacteria as effective biocontrol agents.

Multiple toxins and a protease contribute to the aphid‐killing ability of Pseudomonas fluorescensPpR24

“…In this work, we have sought to gain insight into the mechanisms employed by P. fluorescens PpR24 to kill aphid pests, a largely understudied area. Our previous work (Paliwal et al, 2022) showed PpR24 to be particularly effective in the killing of six aphid species. However, in similar toxicity assays variations in aphid killing efficacy were demonstrated indicating significant variations in both aphid susceptibility and bacterial pathogenicity.…”

“…A list of all bacteria and aphids used in this study is provided in Table S1 and media and growing conditions are described in Paliwal et al (2022). In brief, King's medium B (KBM) plates (King et al, 1954) and Lysogeny Broth (LB) (Miller, 1972) were used to grow PpR24 and Escherichia coli at 27°C and 37°C, respectively.…”

“…The total RNA of the control and infected aphids was prepared using the RNeasy Mini kit (Qiagen, UK). To extract total RNA from aphids, the control and bacteria‐inoculated aphid sachets (Paliwal et al, 2022) were prepared in four replicates. Four biological bacterial replicate cultures were used to infect aphids in four different sachets each consisting of 10 aphids.…”

“…We have previously described a range of bacterial plant isolates that are pathogenic to different species of aphids (Paliwal et al, 2022). One of these, P. fluorescens PpR24, was found to colonize different plant species and showed an excellent ability to control aphid infestations.…”

“…Pseudomonas strains exhibit insecticidal activity against agricultural pests including aphids. It is assumed that ingested bacteria can pass through the aphid gut, from the mouth onto the distal end of the foregut, and then to the midgut (Flury et al, 2016; Paliwal et al, 2022; Stavrinides et al, 2009). However, the differential acidity and hydrolytic enzymes within the aphid gut can inhibit or kill ingested microorganisms (Cristofoletti et al, 2003).…”