Plant infected with bacteria alerts healthy species – 10/18/2023 – Science

A bacterial disease known as lethal tanning has been devastating about 20 species of palm trees in the southern United States over the past two decades. The phytopathogen is already present in Caribbean countries and could soon reach Brazil.

A study conducted by Fapesp postdoctoral fellow Jordana Alves Ferreira showed that infected plants release high concentrations of volatile compounds capable of alerting healthy palm trees around them to a possible threat. These gases, described for the first time in the scientific journal Plants, could be used in the manufacture of inputs to treat the infection.

Caused by phytoplasma Candidatus Phytoplasma aculeata and spread to the plant by the insect vector Haplaxius crudus During its feeding, lethal tanning causes the leaves to darken, rot and die of the palm tree due to clogging of the phloem flow (tissue through which the sap is transported).

The process is followed by the fall of the crown of the Sabal palmetto tree, native to Florida. In addition to being responsible for significant economic losses for landscaping and nursery companies, it also reduces the protection these plants offer against flooding through rainwater evapotranspiration.

In the case of Brazil, it is estimated that the damage would be significant: the country has around 280 thousand hectares cultivated with coconut trees and produces 2 billion fruits per year for food, according to the Brazilian Agricultural Research Corporation (Embrapa).

The research carried out by Ferreira at Embrapa Meio Environment aimed to seek treatment options for infected palm trees.

In previous work, conducted at the University of Florida, in Davie (United States), with support from a Research Internship Abroad Grant (BEPE), the researcher tested the application of treatments with bioformulations directly inside plants (a technique known as plant endotherapy). using pressurized endotherapeutic equipment specific to palm trees and developed in Brazil.

Previous tests, the results of which were published in the journal Analytical Methods, had already shown the technique’s ability to control coconut caterpillars, which cause damage among national producers, quickly and with less product.

In the most recent study, the scholarship holder developed an analysis method that involves the gas chromatography technique coupled to mass spectrometry (GC-MS) and showed that the leaves of infected palm trees release high concentrations of volatile biomarkers (the hexanal and E-2-hexenal compounds) that warn nearby plants of a possible threat. These, in turn, began to release other types of markers (3-hexenal and Z-3-hexen-1-ol), known to be emitted by plants under stress, characterizing communication between plants through volatiles. Palm trees that are not infected or threatened do not release the biomarkers.

“The substance produced by the plant itself in an attempt to heal, defend itself and alert others is also a powerful antibiotic, which can be used in the development of new bioformulations to treat palm trees using plant endotherapy”, says Ferreira, who recently published a review article on the technique in Agriculture magazine.

Natural and widely used solution

Although additional studies are still needed to detail the production of volatile compounds, the discovery paves the way for a series of treatment possibilities for plants in agriculture. Examples are the evaluation of compounds that can be used to treat infections, creation of stimuli for plants to generate their own defenses, development of food deterrents and attractants for natural enemies of H. crudus.

In the United States, specifically, the great advantage would be to have at hand a natural substance alternative to the synthetic antibiotic traditionally used – oxytetracycline, not used in Brazil –, capable of causing environmental problems such as the resistance it generates.

“It is also important to highlight that both the discovered volatiles and endotherapy can be alternatives to be tested in the treatment of diseases in other perennial plants”, adds Sônia Cláudia do Nascimento de Queiroz, researcher at Embrapa Meio Environment and supervisor of the study.

The article Identification of Green-Leaf Volatiles Released from Cabbage Palms (Sabal palmetto) Infected with the Lethal Bronzing Phytoplasma can be read at www.mdpi.com/2223-7747/12/11/2164.