Despite Control Measures, Disease Affecting Orange Production Still Circulates in São Paulo state (Brazil) After 50 Years
16 January 2025
- Citrus canker, a bacterial disease affecting orange and lemon orchards, has been the target of control and eradication programs in São Paulo state (Brazil) since the 1960’s.
- Despite the measures taken, a study points to the persistence, diversification, and adaptation of the causative bacteria over this period.
- Results indicate that strategies based on genetic knowledge of bacterial strains may be key to more effective control.
After five decades of efforts to eradicate citrus canker, one of the most damaging bacterial diseases to orange production, the threat persists in São Paulo orchards. This is according to a study published on Thursday (16) in the scientific journal Microbial Genomics. Conducted through a partnership between São Paulo State University (UNESP), the University of São Paulo (USP), and Manchester Metropolitan University (UK), the research details the genetic evolution of the bacterium Xanthomonas citri, which causes the disease, in São Paulo's citrus-producing regions. The findings may pave the way for more effective combat strategies, considering the genetic differences among local strains of the microorganism.
To understand the distribution and evolution of the citrus canker pathogen in São Paulo orchards, researchers collected samples of leaves showing symptoms of the disease in 13 municipalities between 2018 and 2021. The collected material was scraped, treated, and incubated to allow the growth of the bacteria, which were then subject to genetic analysis. The data obtained were combined with information from scientific databases, enabling the construction of a phylogenetic tree for Xanthomonas citri strains in São Paulo. In total, 1,488 bacterial genomes were studied. The team also investigated and mapped the pathogen's distribution in each region, assessing how it evolved over time in the state.
The results revealed that both early-detected and newer strains of this microorganism continue to compromise production. The varieties identified in the region belong to seven different genetic groups, with the predominant one, named L7, emerging alongside the expansion of orange juice production in Brazil around 1964. According to the study, this group experienced a population decline between 2000 and 2010, a period when eradication protocols became stricter. However, from 2009 onward, relaxed regulations coincided with a rise in the disease’s incidence, which rapidly increased from 0.14% to about 1% in just two years. The study also identified a more recent subdivision within the group, called L7.1, which appears to have emerged in the state in the mid-2000s.
The simultaneous persistence of different strains underscores the need to revise current strategies. “The eradication protocols adopted over the years were, to some extent, effective in maintaining low levels of the disease; however, it has never been eradicated in the country,” says Henrique Ferreira, the study's lead author. He explains that current recommendations combine various approaches, including the use of barriers to minimize bacterial spread and, since 2017, the application of copper sprays. “But there is concern about the fact that copper is a cumulative metal and may contribute to the development of bacterial tolerance or even resistance in the long term,” he warns. “If we need to increase copper doses continuously, we will face greater environmental contamination and reduced bactericide efficiency,” the author adds.
Ferreira argues that the study's findings could support the development of more sustainable and precise control alternatives, tailored to the genetic specificities of strains in each region. “By monitoring strains, we can identify new disease introductions, new varieties, and track their spread, as well as the emergence of concerning characteristics such as resistance to current pesticides,” he adds.
Ferreira and his team, affiliated with the Research Center for Biology of Bacteria and Bacteriophages (CEPID B3), plan to deepen their research on citrus canker, focusing on alternatives to copper use. “For instance, we aim to advance studies on biological control mediated by viruses that infect Xanthomonas citri, thereby developing control strategies with minimal environmental impact,” he predicts. “With the results of our study, we can explore potential genetic and phenotypic differences related to strain virulence and how populations from different regions respond to new bactericidal compounds,” the researcher concludes.
The paper: 'Evolution and spread of Xanthomonas citri subsp. citri in the São Paulo, Brazil, citrus belt inferred from 758 novel genomes' by Caio Felipe Cavicchia Zamunér, Dennis Carhuaricra-Huaman, Roobinidevi Ragupathy, James Redfern, Carmen L. Rodriguez-Cueva, Franklin Behlau, Mark C. Enright, Henrique Ferreira and João C. Setubal, published in Microbial Genomics is avalible at the following:
URL: https://www.microbiologyresearch.org/content/journal/mgen/10.1099/mgen.0.001338
DOI: https://doi.org/10.1099/mgen.0.001338
For more information contact: Henrique Ferreira - [email protected]