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Unravelling Citrus Huanglongbing Disease

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Front. Plant Sci. | doi: 10.3389/fpls.2018.01890

Field Evaluation of Integrated Management for Mitigating Citrus Huanglongbing in Florida

 Yongping Duan1*,  Muqing Zhang2,  Chuanyu Yang2, Charles A. Powell2,  Jihua Wang3, Youzong Huang3 and  Pasco B. Avery2
  • 1U.S. Horticultural Research Laboratory, United States
  • 2Indian River Research and Education Center, University of Florida, United States
  • 3Guangxi University, China

Citrus huanglongbing (HLB) is extremely difficult to control because the psyllid-transmitted bacterial pathogen resides inside the citrus phloem and the disease is systemic. In Florida, the nine billion dollar citrus industry has been significantly impacted by severe HLB epidemics. To combat citrus HLB, in this study we implemented an integrated strategy that includes chemotherapy, thermotherapy, and additional nutrition treatment in three different field trials over three consecutive years. In these trials, only trees already showing HLB symptoms with Ct values ranging from 25.1 to 27.7 were selected for treatments. To assess the complex interactions, we used several methods for evaluating the effectiveness of integrated management, including the slopes (b) of the Ct increase (dy/dt), the pathogenic index (PI) and the decline index (DI) from Ct value and tree scores, and the therapeutic efficacies from PI and DI. This comprehensive analysis showed that most of the tested chemicals were effective to some degree in killing or suppressing the Las bacterium, with higher therapeutic efficacies seen for Grove B, where citrus trees were severely affected by HLB, and it had a higher number of psyllids, relative to Grove E and P in the first two years. Trunk-injected penicillin G potassium was the most effective chemical treatment in all groves, followed by Oxytetracycline Calcium Complex, and Silver Nitrate delivered as foliar sprays. Although the steam heat treatment and additional nutrition did not eliminate or suppress Las over the long term, these treatments did positively affect tree growth and recovery in the short term. Overall, our results provide new insights into HLB control method and strategy for integrated management for HLB epidemic plantations.

Keywords: Citrus huanglongbing. , integrated management, chemotherapy, thermotherapy, Candidatus Liberibacter asiaticus, Las bacterial titers, HLB index

Received: 06 Sep 2018; Accepted: 06 Dec 2018.

Edited by:

Rhuanito S. Ferrarezi, University of Florida, United States

Reviewed by:

Rachid Lahlali, Ecole Nationale d'Agriculture de Meknès, Morocco
Juliana Freitas-Astua, Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), Brazil  

Copyright: © 2018 Duan, Zhang, Yang, Powell, Wang, Huang and Avery. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Yongping Duan, U.S. Horticultural Research Laboratory, Fort Pierce, United States, Yongping.duan@ars.usda.gov