Ultraviolet radiation is capable of controlling sour rot in lime orange

A Ultraviolet C (UVC) radiation, applied in adequate doses, is capable of efficiently control sour rot of lime orange. Caused by a fungus, this disease is the second most common disease affecting fruit after harvest. A discovery of the new treatment came from studies conducted by Embrapa Meio Ambiente (SP) and the State University of Campinas (Unicamp), in a research that aimed to identify the fungus causing the problem.

O UVC treatment had the advantage of resulting in fruits with greater firmness, does not alter its physicochemical characteristics, and delays the maturation process.

A From the isolation of the microorganism, scientists obtained their morphological and molecular identifications (DNA analysis). In these works, they confirmed that the pathogen is the Geotrichum citri-aurantii. “This identification is important, as it provides information important information about the characteristics of the pathogen, helping to propose the best method for controlling the disease”, explains environmental engineer Adriane Maria da Silva, who carried out the research for his master's degree at Unicamp.

Orange fungi

According to Embrapa researcher Daniel Terao, Silva's co-supervisor, fungi are the major causes of post-harvest diseases in citrus fruits. This occurs because the acidic pH of these fruits provides a favorable environment for development of the microorganism.

O The main site of infection is wounds and natural openings in the epidermis of the fruit. In these gaps, green mold, blue mold and sour rot. As an aggravating factor, the fungicides used (thiabendazole and imazalil) have not shown effective specific control of sour rot, which leaves this disease without a product to control it.

In addition Furthermore, scientists warn that the frequent use of these chemical substances can cause negative impacts on human health and the environment, in addition to contribute to the development of pathogens resistant to the molecules used. “It is therefore crucial to encourage the development and commercialization of alternative and sustainable technologies to the use of agrochemicals”, argues the researcher.

For Terao, the discovery paves the way for the development of control methods more sustainable alternatives because they do not use chemicals. "This too makes the national fruit capable of being exported to international markets that restrict the use of chemicals, like the European one, for example”, highlights Terao.

UVC and hydrothermal treatments

Silva studied two methods of controlling sour rot: hydrothermal treatment and exposure to UVC radiation. She verified in in vitro studies that the spores in G. citri-aurantii they are thermoresistant materials and that the inhibition of their important activities occurs from 62°C. On the other hand, studies of the effect of UVC radiation revealed that the inhibition of spore germination occurs at a very low dose, and reaches be completely inhibited at the appropriate dose, demonstrating that they are quite sensitive to radiation.

At evaluation of the effect of temperature combined with UVC radiation on the germination of spores, the level of thermal exposure for 35 seconds at 62°C, combined with the adequate dose in UVC radiation, completely inhibited the germination of spores of G. citri-aurantii.

In previous studies, Terao found that treatments combined involving several technologies can provide an inhibition synergistic of microorganisms. “I observed that, combining the treatment hydrothermal and UVC radiation, there was better control of green mold in pear orange”, he reports.

At the However, in the recent in vivo study, to evaluate the individual effect and combined with temperature and UVC radiation applied directly to the fruit, it was found that the hydrothermal treatment did not adequately control the severity of sour rot caused by G. citri-aurantii, as it is a fungus thermoresistant, as demonstrated by in vitro studies; and what temperatures above 70°C increased the severity of the disease, in addition to causing scalds. fruit epidermis.

Per On the other hand, the irradiation of fruits applied alone showed efficiency in controlling sour rot superior to applied hydrothermal treatment alone or combined with radiation. According to the results, the The application of radiation was efficient, providing control of the disease.

Learn about orange sour rot

A Sour rot was first detected in California, United States, in 1976, and its incidence has increased in recent years, mainly in rainy seasons.

You Greater losses have been observed in export fruit shipments, a since importers, in addition to rejecting the product, charge the producer for costs of transporting and incinerating the cargo. The incident still has repercussions negatively on the producer's image and credibility.

Us Initially, moist, shiny, colored lesions appear on the fruits. light brown. Then, extracellular enzymes produced by the fungus degrade the peel and juice vesicles, forming a watery mass at the site. Under conditions of high temperature and relative humidity of the air, in the epidermis of the fruit, a white, wrinkled mold. As a result, there is a bitter or sour rot, with a strong putrid odor, which attracts dipterans, such as vinegar flies, which lay their eggs in the decomposed tissues of fruits affected, which, in a short time, are full of larvae and mosquitoes (information Embrapa Temperate Climate).

Silva confirmed in their research that the greatest loss caused by sour rot occurs during the rainy season in the state of São Paulo, reaching up to a fifth of the harvested product. With the predominance of rain during the summer, infections increase considerably due to environmental conditions of temperature and relative humidity, which favor the attack and multiplication of the fungus.

National production

O Brazil is the largest orange producer. In the 2019 harvest, around 17 million tons in an area of ​​590 thousand hectares, with a value of R$9 millions. The most significant production is in the state of São Paulo, with around 13 million tons per year, according to the Brazilian Yearbook of Horti and Fruit of 2021.

A the lime type was the second most sold orange variety in Company of Warehouses and General Warehouses of São Paulo (Ceagesp), in 2019, being found in all months of the year, however, with greater supply from July to October. In the orange family, lime occupies third place in concentration of vitamin C, behind the natal and bay. With originating in Southeast Asia, the lime is a large, sweet species, with low acidity and many nutrients.

A dissertation was presented at Unicamp by Adriane Maria da Silva, supervised by professor Juliana Fracarolli, and co-supervised by Daniel Terao, from Embrapa Environment. In addition to Embrapa and Unicamp, the research was supported by company Alfacitrus.