UFSCar research proposes strategies to combat greening

Researchers from the Natural Products Laboratory (LPN) at the Federal University of São Carlos (UFSCar) have presented advances in combating greening. Their studies propose strategies for early diagnosis, vector insect control, and climate-based prediction of spread.

Greening disease—also called Huanglongbing (HLB)—is already affecting nearly half of the orchards in São Paulo and Minas Gerais, according to a recent study. Caused by the bacterium Candidatus Liberibacter asiaticus and transmitted by Asian psyllid (diaphorina citri), the disease still has no cure and causes great economic losses.

Reaction to infection

One study investigated how citrus plants respond to infection. PhD student Jéssica Cristina Amaral, supervised by Professor Maria Fátima das Graças Fernandes da Silva, analyzed secondary metabolites produced by the plants.

The presence of compounds such as xanthyletin and seselin—from the pyranocoumarin class—increased in infected roots. These substances, with known antimicrobial properties, may play an active role in defense against the bacteria. Early detection of these metabolites could serve as the basis for new diagnostic methods and genetic improvement.

Essencial oils

Another 2016 study analyzed essential oils from 22 citrus genotypes grown in Brazil. Olfactometer tests measured the attraction or repulsion of psyllids to different scents. Orange jasmine (Murraya paniculata), the insect's host plant, attracted more than 70% of the individuals. Less attractive genotypes, however, presented compounds such as phytol, (Z)-β-ocimene, and β-elemene. The hypothesis is that these substances act as natural repellents.

Climatic factors

The team also developed a statistical model to predict the spread of greening based on climate factors. The research, conducted in partnership with Fundecitrus, Unifesp, CNPq, and Fapesp, allows us to identify times and regions of greatest risk.

The system takes into account variations in temperature, humidity, and rainfall. This enables preventive measures, such as applying pesticides or removing infected plants, based on the weather forecast.

The model can be adapted to other citrus-growing regions, such as the United States, Mexico, China, and Europe. The proposal doesn't replace existing practices in the field, but it does increase decision-making accuracy.

The results were published in the journals Infectious Disease Modeling (doi.org/10.1016/j.idm.2024.09.005) and Molecules (doi.org/10.3390/molecules21060814), in addition to Amaral's doctoral thesis, available at the UFSCar Institutional Repository ("Alteration in the metabolome and gene expression in the pyranocoumarin biosynthesis pathway in Citrus sinensis x Citrus limonia in response to Huanglongbing").