Abstract
Huanglongbing (HLB) is a destructive disease, associated with psyllid-transmitted phloem-restricted pathogenic bacteria, which is seriously endangering citriculture worldwide. It affects all citrus species and cultivars regardless of the rootstock used, and despite intensive research in the last decades, there is no effective cure to control either the bacterial species (Candidatus Liberibacter spp.) or their insect vectors (Diaphorina citri and Trioza erytreae). Currently, the best attempts to manage HLB are based on three approaches: (i) reducing the psyllid population by intensive insecticide treatments; (ii) reducing inoculum sources by removing infected trees, and (iii) using nursery-certified healthy plants for replanting. The economic losses caused by HLB (decreased fruit quality, reduced yield, and tree destruction) and the huge environmental costs of disease management seriously threaten the sustainability of the citrus industry in affected regions. Here, we have generated genetically modified sweet orange lines to constitutively emit (E)-β-caryophyllene, a sesquiterpene repellent to D. citri, the main HLB psyllid vector. We demonstrate that this alteration in volatile emission affects behavioral responses of the psyllid in olfactometric and no-choice assays, making them repellent/less attractant to the HLB vector, opening a new alternative for possible HLB control in the field.
Highlights
Huanglongbing (HLB) is currently considered the most serious disease of citrus as it is devastating citriculture almost worldwide
To obtain constitutive synthesis of (E)-β-caryophyllene, a T-DNA harboring the genomic sequence of A. thaliana (E)-βCARYOPHYLLENE SYNTHASE TPS21 (AtCS) under the control of the 35S promoter plus the nptII selectable marker gene cassette was constructed
AtCS expression was evaluated in leaves from young shoots, the most attractive leaf stage to D. citri and the most interesting target tissue to induce (E)-β-caryophyllene emission
Summary
Huanglongbing (HLB) is currently considered the most serious disease of citrus as it is devastating citriculture almost worldwide (reviewed in Bove, 2006; Gottwald, 2010; da Graça et al, 2016; Zheng et al, 2018). HLB-infected trees decline in productivity and fruit quality and, in aggressive situations, even die within a few years, inducing severe economic losses to the growers (Bassanezi et al, 2009). Since HLB detection in Florida (United States) in 2005, millions of trees have been killed, production volume has decreased by more than 74%, and annual economic losses are estimated at hundreds of million $ (Hodges et al, 2014; Singerman and Rogers, 2020). Despite intensive chemical control programs, HLB infection, which before 2004 was restricted to Asia, Eastern Africa, and the Arabic Peninsula, is currently present in all major citrus-producing areas except Australia/New Zealand and the Mediterranean basin
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