Researchers discover yeast against mango rot fungus

Scientists Embrapa Environment (SP) found a yeast that controls the Botryosphaeria dothidea, an important fungus that causes mango stem rot. The microorganism is not controlled by conventional chemical application methods or post-harvest heat treatment. Therefore, the researchers' discovery Bernardo Halfeld Vieira, Daniel Terao e Katia Nechet is capable of generating a solution to the problem without leaving chemical residues on the fruits, which, in addition to being healthier for human health, avoids international barriers from countries that do not accept chemical treatments.

Vieira points out that this pathogen is capable of making mango exports unfeasible in the first half of the year. This depends on the climatic conditions, mainly the rains during the flowering and fruiting period.

Biocontrol using yeast proved to be more efficient than chemical treatment with the fungicide thiabendazole, which is normally used. Production of any inhibitory substance by the yeast was not detected, therefore, there is no involvement of an active principle.

The biological control agent Candida membranifaciens it was the yeast that showed greater effectiveness when compared to the fruit treated with fungicide during the 11-day storage period. In contrast, the control fruits (without fungicide treatment and without yeast application) were completely rotten before the end of the experiment.

"There is not yet a cost estimate because only experimental tests were carried out, there is not yet a formulated product”, explains the researcher. Conventional treatment is only based on fungicides. The one currently used combines hydrothermal, by immersing the fruit in hot water, using fungicides, which leave chemical residues and have not been shown to be effective in controlling the disease.

“The study showed that competition, as well as the formation of a layer of yeast in possible sites of infection after colonization, plays an important role in reducing the severity of mango stem rot”, says Vieira.

The app

Researcher Daniel Terao predicts that a combined hydrothermal treatment will be carried out with the subsequent application of the biological product. The fruits would be treated first by spraying hot water, over rolling brushes, at a suitable temperature and for a short period of time, to control the fungus without affecting the quality of the fruit, followed by cooling with cold water, to interrupt the effect of temperature. high. Then, the biocontroller would be applied by spraying the yeast suspension via spray, at the recommended concentration. The specialist emphasizes that the treatment parameters and protocol are in the development phase.

Yeast competes with rot fungus

The results show that the mechanism responsible for controlling the disease by yeast is not related to either antibiosis (action of substances produced by yeast) or parasitism. Scientists explain that the result is obtained because the yeast competes with the rot fungus, forming a film in the place where the pathogen infects. This forms a mechanical barrier between the surface of an occasional bark wound and the pathogen, promoting effective biological control against post-harvest pathogens.

“Yeasts are able to compete for the essential resources necessary for the growth of the rot fungus, in a step before the pathogen penetrates, affecting its ability to cause infection”, details the Embrapa researcher.

As the fungus that causes stem rot remains quiescent, that is, dormant in the fruit until it begins to ripen, the yeast will be more efficient if it is present on the skin of the fruit while it is still green. Therefore, symptoms are only observed in the post-harvest phase. Therefore, the best way to carry out the treatment would be to apply a suspension of microorganism cells by spraying on unripe fruits, promoting disease control and ensuring the absence of toxic residues of the fungicide in the fruits.

Vieira explains that some yeasts that had already demonstrated biological control activity were selected from the Embrapa Meio Ambiente collection. “We decided to test for this disease in mangoes, which is becoming very important. In addition to the tests, we had to know how they exercise this control, so the work was done along these lines.”

The researchers worked with the living cell in the laboratory. Therefore, the product is not yet formulated. "In theory it is not complicated, it would be the same sachet, preserved for the long term and designed to dissolve in water and be used as a spray. The most important thing is that the yeast is alive", he emphasizes Vieira.

According to the history recorded in the research, this disease is caused by a fungus that resists treatment at higher temperatures. “The fungicide used for a similar disease is not working”, informs the researcher, highlighting the advantage of the yeast not leaving residues because it does not produce metabolites.