Canine olfactory detection of a vectored phytobacterial pathogen, Liberibacter asiaticus, and integration with disease control

Abstract

Early detection and rapid response are crucial to avoid severe epidemics of exotic pathogens. However, most detection methods (molecular, serological, chemical) are logistically limited for large-scale survey of outbreaks due to intrinsic sampling issues and laboratory throughput. Evaluation of 10 canines trained for detection of a severe exotic phytobacterial arboreal pathogen, Candidatus Liberibacter asiaticus (CLas), demonstrated 0.9905 accuracy, 0.8579 sensitivity, and 0.9961 specificity. In a longitudinal study, cryptic CLas infections that remained subclinical visually were detected within 2 wk postinfection compared with 1 to 32 mo for qPCR. When allowed to interrogate a diverse range of in vivo pathogens infecting an international citrus pathogen collection, canines only reacted to Liberibacter pathogens of citrus and not to other bacterial, viral, or spiroplasma pathogens. Canines trained to detect CLas-infected citrus also alerted on CLas-infected tobacco and periwinkle, CLas-bearing psyllid insect vectors, and CLas cocultured with other bacteria but at CLas titers below the level of molecular detection. All of these observations suggest that canines can detect CLas directly rather than only host volatiles produced by the infection. Detection in orchards and residential properties was real time, ∼2 s per tree. Spatiotemporal epidemic simulations demonstrated that control of pathogen prevalence was possible and economically sustainable when canine detection was followed by intervention (i.e., culling infected individuals), whereas current methods of molecular (qPCR) and visual detection failed to contribute to the suppression of an exponential trajectory of infection.

Evaluation of the control effect of SAR inducers against citrus Huanglongbing applied by foliar spray, soil drench or trunk injection

“…However, in many citrus producing areas where HLB is endemic or has high incidence, such as Florida, inoculum eradication is largely abandoned (Graham et al 2020). Intriguingly, despite that Las has not been cultured in artificial media, promising advances have been made that might help develop long-term solutions to control HLB, including understanding the virulence mechanisms of Las (Duan et al 2009;Jain et al 2018;Pitino et al 2018;Chen et al 2020;Clark et al 2020;Pandey et al 2020;Pang et al 2020;Thapa et al 2020a;Thapa et al 2020b;Vasconcelos et al 2020), improving Las detection (Kim and Wang 2009;Pagliaccia et al 2017;Pandey and Wang 2019;Gottwald et al 2020), and developing tolerant or resistant citrus varieties using traditional and novel approaches (Jia and Wang 2014;Rawat et al 2015;Deng et al 2019;Jia et al 2019;Jia and Wang 2020). In addition, in HLB-endemic regions, such as Florida, the HLB management focus has shifted to how to improve and sustain the productivity at the presence of HLB.…”

Status of Huanglongbing (HLB) outbreaks in Florida, California and Texas

“…These infections range from incipient, i.e., within 2 weeks of CLas transmission by ACP, to advanced infections several years old. Accuracy is 99.1%, 95.6%, and 91.9% in young trees, commercial orchards, and residential properties, respectively, when sniffing a tree for 1-2 s, regardless of age or canopy size (Gottwald et al 2020). The canines can also detect CLas+ ACP and CLas bacteria in culture, indicating that canines are detecting CLas VOCs directly (Gottwald et al 2020).…”

“…Accuracy is 99.1%, 95.6%, and 91.9% in young trees, commercial orchards, and residential properties, respectively, when sniffing a tree for 1-2 s, regardless of age or canopy size (Gottwald et al 2020). The canines can also detect CLas+ ACP and CLas bacteria in culture, indicating that canines are detecting CLas VOCs directly (Gottwald et al 2020). The CLas-detector canines are being deployed by commercial growers in Southern California and Northern Florida where CLas incidence is still low and difficult to detect.…”

A perspective of citrus Huanglongbing in the context of the Mediterranean Basin

“…A simple method has been developed to detect Las right after psyllid feeding, which allows early detection of Las before HLB symptom appearance (Pandey and Wang 2019). Importantly, canines have shown excellent sensitivity and accuracy in detecting Las directly rather than only host volatiles produced by the infection (Gottwald et al 2020), which might help both in early detection of Las in the citrus groves and backyards as well as in quarantine measures.…”