Abstract
Simple SummaryThe iconic citrus crop of Florida is suffering from an incurable disease called Huanglongbing (HLB), or citrus greening. HLB is caused by a bacterium Candidatus Liberibacter asiaticus (CLas), which is efficiently vectored by a small insect, the Asian citrus psyllid (ACP). To control the spread of CLas and ultimately HLB, citrus growers primarily depend on environmentally harmful insecticides against the ACP, which can induce insecticide resistance. An alternative, biological approach involves insect-specific viruses (ISVs) of the ACP for future exploitation to exclusively target this insect pest. To identify these ISVs, we have subjected ACPs to high-throughput sequencing, a powerful sequencing technology. This current study follows an initial detection of citrus tristeza virus (CTV) amongst the viruses detected in the ACP during HTS and continues to show the persistent and diverse presence of CTV in Florida ACPs across subsequent years. We suggest that the ACP may be utilized as a tool or lens of CTV presence throughout Florida citrus groves.The destructive citrus disease, Huanglongbing (HLB) or citrus greening, continues to devastate Florida’s citrus industry. A hemipteran insect, the Asian citrus psyllid (ACP), disperses Candidatus Liberibacter asiaticus, one of the putative bacterial pathogens of HLB. This study builds upon ongoing research utilizing high-throughput sequencing to analyze the virome of ACP populations collected from citrus groves throughout Florida. Following the widespread detection of sequences aligning to the genome of citrus tristeza virus (CTV) across consecutive years in the Florida ACP virome, we continued to detect a pervasive amount of CTV in Florida ACPs during subsequent years. Simultaneously, we also detected mixed infections of CTV strains in pooled ACPs from different Florida regions. Predating the HLB epidemic, CTV has been present in Florida for many years and our results confirm its widespread and diverse persistence in Florida citrus groves through a unique lens, the ACP. CTV presence in the ACP likely results from feeding on CTV-infected citrus trees in Florida citrus groves, which may help to understand an overlapping presence of CTV and HLB, both endemic citrus pathosystems in the state, and their role in future integrated pest management strategies.
Highlights
Florida citrus groves face overwhelming devastation from the disease Huanglongbing (HLB) or citrus greening
Based on the Kruskal–Wallis test and Dunn’s test of the reads per kilobase per million sequenced (RPKM) means, significant differences between the relative abundance of the viruses were observed in Group 2019, the Asian citrus psyllid (ACP)-associated Diaphorina citri associated C virus (DcACV) relative abundance was significantly higher than transcripts detected from the bacteriophage Wolbachia phage (WO) (Table 4)
Virome analysis of Florida ACP populations enabled a unique viewpoint of the decades-long presence of citrus tristeza virus (CTV) in Florida citrus groves and showed an overlap with the HLB epidemic throughout the state
Summary
Florida citrus groves face overwhelming devastation from the disease Huanglongbing (HLB) or citrus greening. Reducing dependence on environmentally harmful insecticides to control the ACP motivates research for identifying potential biological alternatives. Such biological controls include microorganisms naturally present in the ACP, viruses known as insect-specific viruses (ISVs) [4,5]. Nouri et al [4] and subsequent studies expanded ISV analyses in the ACP using metagenomics of worldwide ACP populations and identified several novel ACP-associated viruses [7,8]. The endemic presence of HLB and the ACP in Florida citrus groves prompted a need to apply HTS solely to field populations of Florida ACPs originating from commercial citrus groves throughout the state with a goal to identify potential ISVs suitable for biological control of the ACP [10]
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