Research uses organic molecules as pesticides against citrus canker

A study conducted by UFSCar (Federal University of São Carlos) has developed a technique that uses organic molecules derived from sugars as active ingredients for pesticides against citrus canker. This disease, one of the main issues in citrus orchards, is traditionally controlled through copper spraying.

The research employed proteomic analysis, combined with genetics, to identify target proteins in the bacteria that contribute to their ability to cause the disease. One of the targets found on the cell surface was the protein named XanB. The group recently demonstrated that organic molecules derived from carbohydrates, which inhibit the target protein XanB, were effective in controlling the disease and could serve as active ingredients for new pesticides.

The startup BionFarm will now evaluate directly in orchards whether these inhibitors block an enzyme in the bacteria, without which the disease cannot progress. Field tests will involve formulations based on eugenol, a dark brown oil extracted from cloves (Syzygium aromaticum). Eugenol and other essential oils, such as oregano (Origanum vulgare) and lemongrass (Cymbopogon spp.), which also showed promising results in greenhouse tests, constitute the second generation of compounds being tested against X. citri.

Henrique Ferreira from São Paulo State University (Unesp) developed other compounds in collaboration with colleagues from two universities in the Netherlands and is working on the formulation with experts from the Brazilian input company Santa Clara Agrociência. "We have over 15 formulations, already tested and validated in greenhouses, in the phase of economic feasibility studies," he said.

According to André Alexandrino, a partner at the startup BionFarm, the enzyme inhibitors could compete in price with copper, potentially offering an alternative to the traditional pesticide sprayed against citrus canker. The efficiency of both types of compounds was found to be equivalent in greenhouse tests. 

"The price of agricultural defenses made with copper is still unbeatable, but we are preparing for when European consumers no longer want to buy citrus treated with copper," commented Ferreira, who is part of the Research Center in Bacteria and Bacteriophage Biology.

Research

The research was led by chemist and pharmaceutical-biochemist Maria Teresa Marques Novo Mansur from the Applied Biochemistry and Molecular Biology Laboratory (LBBMA) at UFSCar. She identified the enzyme phosphomannose isomerase/GDP-mannose pyrophosphorylase (GDP stands for guanosine diphosphate), also known as XanB.

"The main advantage of our research is that we use a novel approach to find an alternative for controlling citrus canker, which allowed us to discover molecules that interfere very specifically with the pathogen-plant interaction and are of low or no toxicity to humans, in contrast to the copper currently used in orchards," the UFSCar professor highlighted.

According to her, the expectation is that these carbohydrate-derived molecules could become an "ecologically attractive alternative, being biodegradable and not interfering with soil microbiota, thus causing less environmental impact, and also being economically viable for commercial use in the field."

"The multidisciplinary approach we used, with complementary methodologies from collaborators in different fields of knowledge, focused on a common goal, allowed us not to stop at basic science, which is valuable in itself, but to go further, generating technological innovation through products of interest to agribusiness," she evaluated.

Field tests are expected to last for two years. "The efficiency of the new compounds tends to be lower than in greenhouses because wind and rain facilitate the entry of bacteria into plants, and the sun can accelerate the degradation of the pesticides," warned agricultural engineer Franklin Behlau from the Citrus Defense Fund (Fundecitrus), who participated in both research projects.

Citrus Canker

Citrus canker is a disease caused by the bacterium Xanthomonas citri subsp. citri, affecting various citrus species. According to the UFSCar researcher, the damage caused by citrus canker to agriculture is mitigated by management measures, primarily through the spraying of copper solutions in infected orchards.

"However, this control incurs costs exceeding R$200 million per season, in addition to causing environmental impact due to the metal's toxicity. Moreover, copper-resistant bacterial strains have already been identified, which reduces the efficiency of this control," concluded André Alexandrino, who holds a PhD from the Biotechnology Graduate Program (PPGBiotec) at UFSCar.

(Editing by Leonardo Gottems, reporter for AgroPages)