Abstract
Huanglongbing (HLB) is the most devastating citrus disease worldwide, and suppression of the Asian citrus psyllid (Diaphorina citri) is regarded as an effective method to inhibit the spread of HLB. In this study, we isolated a strain named as Serratia marcescens KH-001 from D. citri nymphs suffering from disease, and evaluated its killing effect on D. citri via toxicity test and effect on microbial community in D. citri using high-throughput sequencing. Our results indicated that S. marcescens KH-001 could effectively kill 83% of D. citri nymphs, while the fermentation products of S. marcescens KH-001 only killed 40% of the D. citrinymphs. High-throughput sequencing results indicated that the S. marcescens KH-001 increased the OTU numbers from 62.5 (PBS buffer) to 81.5, while significantly lowered the Shannon index compared with Escherichia coli DH5α (group E) (p < 0.05). OTU analysis showed that the S. marcescens KH-001 had significantly reduced the relative abundance of endosymbionts Wolbachia, Profftella, and Carsonella in group S compared with that in other groups (p < 0.05). Therefore, the direct killing effect of the fermentation products of S. marcescens KH-001 and the indirect effect via reducing the numbers of endosymbionts (Wolbachia, Profftella, and Carsonella) of D. citri endow S. marcescens KH-001 a sound killing effect on D. citri. Further work need to do before this strain is used as a sound biological control agents.
Highlights
Huanglongbing (HLB, known as citrus greening) is a devastating citrus disease caused by Candidatus Liberibacter spp., which is first reported in China in 1943 and has been reported in at least 40 citrus producing countries (Bové, 2006)
Our group investigated the killing effects of fermented supernatant of S. marcescens KH-001, Escherichia coli DH5α and S. marcescens KH-001 on D. citri, and we studied their effects on the parasitic microbial diversity in D. citri using high-throughput sequencing method, to explore the possible killing mechanism of S. marcescens KH-001 on D. citri
Forty five strains were randomly selected and identified using biochemical identification and molecular biological identification, and a strain of S. marcescens were selected based on its sound killing effect on D. citri nymphs, which was named as S. marcescens KH-001 and stored at China Center for Type Culture Collection (Registration No CCTCC M 2017465)
Summary
Huanglongbing (HLB, known as citrus greening) is a devastating citrus disease caused by Candidatus Liberibacter spp., which is first reported in China in 1943 and has been reported in at least 40 citrus producing countries (Bové, 2006). There is no cure for HLB once the trees get infected, and traditional HLB managements rely on psyllid control, aggressive removal of infected trees and planting of disease-free nursery trees (Grafton-Cardwell et al, 2013; Alvarez et al, 2016). Las is the most widely distributed HLB pathogen and is vectored by Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Liviidae) (Bové, 2006). D. citri depends heavily on young citrus flush for survival and reproduction, and the feeding and reproductive behavior of D. citri plays an important role in the spread of Las. D. citri adults prefer emerging plant tissues for oviposition (Halbert and Manjunath, 2004), which make young trees prone to Las infection. Suppression or reduction of D. citri has been the primary method to inhibit the spread of HLB (Saha et al, 2017)
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