N-acetylcysteine in citrus plants infected with Candidatus Liberibacter asiaticus: effects on bacterial titer and on the host

Author(s)

Henrique Augusto Siqueira Bergamo

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2019-02-11

Examining board members

Alessandra Alves de Souza; Helvecio Della Coletta Filho; Rafael Vasconcelos Ribeiro; Simone Cristina Picchi

• Advisor: Alessandra Alves de Souza

Abstract

The citriculture stands out for its great importance in the agribusiness of São Paulo and Brazil, being the Brazilian agricultural commodity with greater hegemony in the external market. Important citrus producing regions in the world such as Asia, Americas and Africa have been facing one of the most serious major phytosanitary problem, the HuangLongBing (HLB), also known as greening. In Asia and in the Americas HLB is predominantly caused by the bacterial species Candidatus Liberibacter asiaticus (CLas), which colonizes the phloem vessels of the host plant causing severe leaf and fruit symptoms, affecting plant productivity and fruit quality, both for fruit processing industry and for in natura consumption. In Brazil, the recommended and technically supported and proven management for this disease is based on the principles of exclusion, eradication and protection. However, although it is still mandatory, the eradication of plants with HLB has been increasingly neglected, passing to live with the disease, postponing the plant's economic useful life. Different types of molecules have been used for the management of phytobacteria, having direct action in the pathogen or as plant resistance inductors or potenciationr.. An example is the use of antioxidant molecules such as N-acetylcysteine ??that has shown promising results against Xylella fastidiosa, which causes citrus variegated chlorosis (CVC), and Xanthomonas citri subsp. citri, which causes citrus canker. Antibiotics such as penicillin, tetracycline and streptomycin have been tested against CLas in vitro tests, in vivo and some are already used in the field. The goal of this project was to evaluate the effect of these compounds on sweet orange plants infected with CLas in order to verify the variation of bacterial concentration, the activity of enzymes in response to oxidative stress caused by bacterial infection and the expression of genes related to reactive oxygen species detoxification, mainly from chloroplast, which is the most affected organelle due to the accumulation of starch in it. It could be verified that, despite the invariable bacterial titre in infected plants, there was an induction of the enzymatic activity of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) in the NAC treatments, also accompanied by the overexpression of Chloroplastidial ascorbate peroxidase (APXchl), glutathione chloroplastidial peroxidase (GPXchl) and Cu-Zn superoxide dismutase (Cu-Zn SODchl). In antibiotic treatment, a decrease in the bacterial titre could be observed, however there was no induction of SOD and CAT activity, with the exception of APX. There is strong repression in the expression of chloroplastdial detoxification genes (APXchl, GPXchl and Cu-Zn SODchl), indicating possible toxicity caused by antibiotics. Although the antimicrobial effects of NAC have not been observed in this study. There is still much to study about the action of this promising molecule in agriculture and especially the HLB. Means of delivery in the phloem and the joint action of the NAC with the antibiotics should be taken into consideration (AU)

• FAPESP's process: 16/14877-0 - N-acetylcysteine in infected citrus plants by Candidatus Liberibacter asiaticus: possible effects on the pathogen and host
• Grantee: Henrique Augusto Siqueira Bergamo
• Support Opportunities: Scholarships in Brazil - Master