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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Plant Pathology Research » Research » Publications at this Location » Publication #324876
Title: Mitigating citrus huanglongbing via effective application of antimicrobial compounds and thermotherapy

Author
item YANG, CHUANYU - University Of Florida
item POWELL, CHARLES - University Of Florida
item Duan, Ping
item Shatters, Robert - Bob
item LIN, YOUJIAN - University Of Florida
item ZHANG, MUQING - University Of Florida

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2016
Publication Date: 6/1/2016
Publication URL: http://handle.nal.usda.gov/10113/63199
Citation: Yang, C., Powell, C., Duan, Y., Shatters, R.G., Lin, Y., Zhang, M. 2016. Mitigating citrus huanglongbing via effective application of antimicrobial compounds and thermotherapy. Crop Protection Journal. 84:150-158.

Interpretive Summary: Huanglongbing (HLB), the most devastating citrus disease worldwide, is caused by three species of uncultured, phloem-restricted Proteobacteria, Candidatus Liberibacter asiaticus (Las), Ca. Liberibacter americanus, and Ca. Liberibacter africanus. Currently, there are no effective strategies to control HLB in the fields due to the lack of resistant citrus cultivars and inability to suppress the psyllid vectors. To develop effective strategies against citrus HLB, we combined thermotherapy using different temperatures coupled with chemotherapy using either bark paint or root drench application to Las-infected citrus seedlings. Our results indicated that thermotherapy at 45 C was more effective against Las than thermotherapy at 40 C or 42 C with the treatment regime of 8 hours per day for one week, and enhanced the delivery efficiency of effective chemical compounds into the citrus phloem. Ampicillin (Amp) and a combination of actidione and validoxylamine A (Act+VA) were the most effective chemical formulations against Las. When Amp or Act+VA treatment was combined with thermotherapy, the area under the disease progress curve (AUDPC) was significantly greater than the thermotherapy treatment alone. The Ct value, AUDPCs, and therapeutic efficiency (TE) of Amp and Act+VA treatment applied by bark absorption were greater than those of Amp or Act+VA applied by root drench. Therefore, we propose an eco-friendly chemo-thermotherapy strategy coupled with a bark absorption application method for disease control in HLB-affected citrus plants.

Technical Abstract: Huanglongbing (HLB) is a serious citrus disease that threatens the citrus industry worldwide. HLB is a systemic, infectious disease and the putative causal bacterium Candidatus Liberibacter asiaticus (Las) resides in citrus phloem. In this study, the effects of heat treatment, chemical formulations, and application methods on bacterial titer in the citrus host, measured by quantitative PCR, were evaluated. Thermotherapy at 45 C (Ct = 30.79 ± 6.26) was more effective against Las than thermotherapy at 40 C (Ct = 28.72 ± 6.00) or 42 C (Ct = 28.02 ± 6.25), and enhanced the delivery efficiency of effective chemical compounds into the citrus phloem. Ampicillin (Amp) and a combination of actidione and validoxylamine A (Act+VA) were the most effective chemical formulations against Las. When Amp or Act+VA treatment was combined with thermotherapy, the area under the disease progress curve (AUDPC) was significantly greater than the thermotherapy treatment alone. The Ct value, AUDPC, and therapeutic efficiency (TE) of Amp and Act+VA treatment applied by bark absorption were greater than those of Amp or Act+VA applied by root drench. Therefore, we propose a chemo-thermotherapy strategy coupled with a bark absorption application method for disease control in HLB-infected citrus plants.