Field evaluation of chemotherapy on hlb-affected citrus trees with emphasis on fruit yield and quality

Authors: ZHANG, MUQING - University Of Florida; KARUPPAIYA, PALANIYANDI - Guangxi University; Zheng, Desen; Sun, Xiuxiu; Bai, Jinhe; FERRAREZI, RHUANITO - University Of Florida; POWELL, CHARLES - University Of Florida; Duan, Ping

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2021
Publication Date: 2/22/2021
Citation: Zhang, M., Karuppaiya, P., Zheng, D., Sun, X.N., Bai, J., Ferrarezi, R., Powell, C., Duan, Y. 2021. Field evaluation of chemotherapy on hlb-affected citrus trees with emphasis on fruit yield and quality. Frontiers in Plant Science. 12:611287. https://doi.org/10.3389/fpls.2021.611287.
DOI: https://doi.org/10.3389/fpls.2021.611287

Interpretive Summary: Citrus huanglongbing (HLB) is currently the most devastating citrus disease, and has devastated the Florida's citrus industry since its first report of the disease in Florida in 2005. The industry around the world is in dire need of commercially available and effective antimicrobial compound to control the disease. In this study, we investigated the effects of different antimicrobial chemicals on matured HLB-affected citrus trees with emphasis on the fruit yield and quality. By extensive examining different parameters, such as disease index, tree canopy, fruit yield and quality, we found that penicillin (PEN) with surfactant was most effective in killing the HLB bacteria in infected citrus trees, followed by Fosetyl-Al (ALI), Oxytetracycline (OXY), Carvacrol (CARV), Validamycin (VA). We further analyzed fruit yield and quality, and revealed that PEN treatment increased the soluble solids content (SSC), whereas OXY treatment significantly reduced titratable acidity (TA) level and increased the SSC/TA ratio compared to the control. In addition, nutrient analysis showed increased N and Zn levels in ALI and PEN treatments, and OXY treatment increased leaf P, K, S, and Mg levels compared to untreated control. These findings revealed that some of the chemical treatments were able to reduce the levels of HLB pathogen, to enhance nutritional status in leaves, and to improve tree growth and fruit quality of HLB-affected trees. All together, chemotherapy is effective to a certain degree and may serve as a component of integrated control for HLB.

Technical Abstract: Huanglongbing (HLB) is one of the most devastating diseases of citrus, which is associated with Candidatus Liberibacter asiaticus (Las) in United States. To date, no effective antimicrobial compound is commercially available to control the disease. In this study, we investigated the effects of different antimicrobial chemicals with suitable surfactants on matured HLB-affected citrus trees with emphasis on the fruit yield and quality. Each treatment was applied three times in a two-week interval during the spring flush period, one time in summer, and three times during the autumn flushing period. We extensively examined different parameters, such as pathogenic index, disease index, tree canopy, fruit yield, quality, and nutritional status. The results showed that among the treatments, penicillin (PEN) with surfactant was most effective in suppressing Las titer in infected citrus trees, followed by Fosetyl-Al (ALI), Oxytetracycline (OXY), Carvacrol (CARV), Validamycin (VA). Fruit quality analysis revealed that PEN treatment increased the soluble solids content (SSC), whereas OXY treatment significantly reduced titratable acidity (TA) level and increased the SSC/TA ratio compared to the control. Nutrient analysis showed increased N and Zn levels in ALI and PEN treatments, and OXY treatment increased leaf P, K, S, and Mg levels compared to untreated control. Futhermore, B, Ca, Cu, Fe, and Mn in leaves were reduced in all chemical treatments than that of the untreated control. These findings revealed that some of the chemical treatments were able to suppress Las pathogen, enhance nutritional status in leaves, and improve tree growth and fruit quality of HLB-affected trees.