UFSCar study uses organic molecules derived from sugars as active ingredients for agricultural pesticides
The Federal University of São Carlos (UFSCar), in conjunction with other institutions, is developing a project aimed at finding new inputs to combat citrus canker. The disease, which affects citrus crops - such as lemons and oranges - has been combated for decades by spraying copper, a toxic metal that is harmful to the environment.
The research began around 2009, coordinated by Professor Maria Teresa Marques Novo Mansur, from the Genetics and Evolution Department (DGE) at UFSCar, by searching for target proteins in the bacteria that were involved in their ability to cause the disease through proteomic analysis [of proteins] combined with genetic analysis. One of the targets found on the cell surface was a protein called XanB. The group demonstrated more recently that organic molecules derived from carbohydrates, inhibitors of the target protein XanB, were efficient in controlling the disease and could be active ingredients for new agricultural pesticides.
The work of Novo-Mansur - who is the leader of the research group at the Laboratory of Biochemistry and Applied Molecular Biology (LBBMA) at UFSCar - is being developed with funding from the São Paulo Research Foundation (FAPESP) and in collaboration with the group of Professor Carlos Henrique Tomich de Paula da Silva, from the University of São Paulo (USP), who designed the inhibitor molecules using a computational approach, and the group of researcher Franklin Behlau, from the Citrus Defense Fund (Fundecitrus) in Araraquara, who collaborated on the in vivo tests.
What is citrus canker?
Citrus canker is a disease caused by bacteria Xanthomonas citri subsp. citrus , which affects several species of citrus; it is characterized by the appearance of corky lesions, which are rough and raised eruptions on the leaves, fruits and branches of the plants. These lesions can be surrounded by yellow halos, resulting from the decrease in chlorophyll in the infected areas, and the affected tissues can expel bacteria that spread easily by wind and rain. Infected plants can suffer premature leaf and fruit drop, which reduces fruit quality and productivity, affecting the economic potential of citrus farming.
According to the UFSCar researcher, the damage caused by citrus canker to agriculture can be mitigated by management measures and, mainly, by spraying copper solutions on infected orchards. "However, this control generates costs of over R$200 million per harvest, in addition to causing environmental impact due to the toxicity of the metal. Furthermore, bacterial strains resistant to copper have already been identified, which reduces the efficiency of this control," explains André Vessoni Alexandrino, a PhD student in the Postgraduate Program in Biotechnology (PPGBiotec) at UFSCar who was advised by Professor Novo-Mansur at UFSCar on this project.
Other control measures, according to the researcher, include the eradication of contaminated plants and the use of windbreaks to reduce the spread of the disease. Given the ineffectiveness of these measures for a definitive cure and the environmental impacts, researchers and farmers are looking for new alternatives, such as the development of more resistant cultivars, agents that can act as biological control and compounds that can control the disease in a more sustainable way.
Research advances
"The main difference in our research is that we used a novel approach to search for an alternative for controlling citrus canker, which allowed us to develop molecules that interfere in a very specific way in the interaction of the pathogen with the plant and are of low or no toxicity to humans, in contrast to the copper currently used in crops," highlights the UFSCar professor. "We expect that these molecules, which are derived from carbohydrates, may constitute an ecologically attractive alternative, being biodegradable and not interfering with the soil microbiota, thus causing less environmental impact, and are also economically viable for commercial use in the field. The multidisciplinary approach used, with complementary methodologies from collaborators from different areas of knowledge, focused on a common goal, allowed us not to stop at basic science, which in itself already has its value, but to go further, generating technological innovation through products of interest to agribusiness," she evaluates.
The new compounds are being tested on a larger scale in the field by a start-up company, which licensed the patent for the work, filed with the National Institute of Industrial Property (INPI). At USP, the work had the contribution of Mariana Pegrucci Barcelos, a doctoral student supervised by Professor Tomich, who also completed a master's degree with him on the project. At UFSCar, in addition to André Alexandrino, there was also the participation of Beatriz Brambila, who recently defended her master's degree in the Graduate Program in Evolutionary Genetics and Molecular Biology (PPGGEv-UFSCar), under the supervision of Professor Novo-Mansur. Inhibitors designed by Professor Tomich's group against another target protein of the bacteria, also discovered by the UFSCar group, are being tested by doctoral student Ana Carolina Franco Severo Martelli, under the supervision of Professor Novo-Mansur through PPGGEv-UFSCar, and are also showing promising results, according to the University professor.