Articles
Novel systemic acquired resistance (SAR) inducers for managing huanglongbing (citrus greening) and citrus canker diseases
Article number
1378_18
Pages
133 – 142
Language
English
Abstract
Huanglongbing (HLB; citrus greening), putatively caused by Candidatus Liberibacter asiaticus (CLas), and citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), are the two most devastating citrus bacterial diseases in Florida, USA, and in many other citrus-producing countries worldwide.
Yet, there is no HLB control or prevention method, and only limited control measures against canker including copper.
Copper poses a risk of over-accumulation in the soil as well as developing a copper-resistant Xcc strain.
Thus, there is a pressing need to develop novel therapeutics for long-term disease control in citrus orchards.
This study sought new strategies for combating HLB and canker with foliar spray applications of novel class SAR inducers as a potential preventive measure against HLB and citrus canker across several greenhouse trials.
Three foliar spray applications of PDI5 (500 ppm) on the two-year-old healthy citrus trees (n=20), a week prior to exposure to CLas infected Asian citrus psyllid (ACP) followed by monthly spray applications (100 ppm), effectively delayed CLas infection and HLB symptoms for six months, and bacterial titer in infected trees remained low (average Ct=30). All non-treated trees and those treated with other SAR inducers or bacteriostatic oxytetracycline were infected with CLas, two to four months after ACP exposure, with high bacterial titers (Ct=22-24). In separate experiments, either a foliar spray of PDI5 (500 ppm) or a soil drench application of Actigard (acibenzolar-S-methyl; 2 g tree‑1) significantly reduced leaf canker lesions relative to non-treated control and were comparable to copper sulfate pentahydrate (150 ppm). The disease-prevention mechanism and potential use of the SAR inducer PDI5 in the field for simultaneous management of economically important citrus diseases are currently being evaluated.
Yet, there is no HLB control or prevention method, and only limited control measures against canker including copper.
Copper poses a risk of over-accumulation in the soil as well as developing a copper-resistant Xcc strain.
Thus, there is a pressing need to develop novel therapeutics for long-term disease control in citrus orchards.
This study sought new strategies for combating HLB and canker with foliar spray applications of novel class SAR inducers as a potential preventive measure against HLB and citrus canker across several greenhouse trials.
Three foliar spray applications of PDI5 (500 ppm) on the two-year-old healthy citrus trees (n=20), a week prior to exposure to CLas infected Asian citrus psyllid (ACP) followed by monthly spray applications (100 ppm), effectively delayed CLas infection and HLB symptoms for six months, and bacterial titer in infected trees remained low (average Ct=30). All non-treated trees and those treated with other SAR inducers or bacteriostatic oxytetracycline were infected with CLas, two to four months after ACP exposure, with high bacterial titers (Ct=22-24). In separate experiments, either a foliar spray of PDI5 (500 ppm) or a soil drench application of Actigard (acibenzolar-S-methyl; 2 g tree‑1) significantly reduced leaf canker lesions relative to non-treated control and were comparable to copper sulfate pentahydrate (150 ppm). The disease-prevention mechanism and potential use of the SAR inducer PDI5 in the field for simultaneous management of economically important citrus diseases are currently being evaluated.
Authors
S. Kunwar, A. Redondo, D. Manker, M. Lott, T. Knobloch, S. Brunet, J. Dufour, O. Batuman
Keywords
HLB, Candidatus Liberibacter asiaticus, Xanthomonas citri subsp. citri (Xcc), plant defense inducer, Asian citrus psyllid
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