​Blackened fruits: management of passion fruit black rot

Passion fruit cultivation can be affected by many diseases, some of which limit its cultivation if not adequately controlled. The expansion of cultivation areas in some regions has favored the emergence of new diseases and the worsening of a large number of others that have become economically important.

The evolution of the pathogenicity of microorganisms, stimulated by environmental pressures, has revealed a range of pathogens, previously considered secondary, that have become primary. Until recently considered an occasional pathogen of stressed plants, the fungus Lasiodiplodia theobromae (Pat.) Griff. & Maubl has become a serious problem for producers, as it has become important for several crops, where climatic conditions are favorable to them. This pathogen has a range of more than 500 hosts cataloged in tropical and temperate regions.

Among the hosts, it is possible to mention species that are of great economic importance for the country, such as the cashew tree, the mango tree, the coconut tree, the acerola tree and the passion fruit tree. It is also considered one of the main post-harvest pathogens, due to its high incidence in fruits, which can make its commercialization unfeasible.

In Brazil, post-harvest diseases are responsible for significant losses of agricultural products during the marketing stages. They reduce not only the quantity sold, but also the quality of products on the market. Losses caused by these diseases are variable and fluctuate depending on the product, region and technology used in production. Rot is the main factor in the depreciation of fruits post-harvest, a fact commonly found in passion fruit fruits sold in the municipality of Alta Floresta, Mato Grosso, with a great deal of action being attributed to Lasiodiplodia theobromae, causal agent of black fruit rot.

The gender Passiflora

The passion fruit belongs to the Passiforaceae family, which is widely distributed in the tropics and temperate regions and is made up of 18 genera and more than 630 species. The gender Passiflora It is the most economically important and has 129 known species, native to Brazil, of which 83 are endemic and can be used as food, medicine and ornament. The most cultivated species in Brazil is Passiflora Sims. f. flavicarpa Degenes (yellow passion fruit or sour passion fruit). Yellow passion fruit is of great importance due to the quality of the fruits, its promotion to consumers and the encouragement of the agroindustry. It represents 95% of Brazilian orchards.

When marketing this fruit, appearance is one of the qualitative evaluation parameters most used by consumers, with post-harvest diseases being one of the main factors in the loss of quality of passion fruit fruits.

Black fruit rot

This disease is caused by the fungus Lasiodiplodia theobromae (Pat.) Griff. & Maubl. It is a fungus with a wide distribution and a large number of hosts, considered opportunistic in some cases, showing little pathogenic specialization, generally associated with susceptible hosts such as stressed plants, with natural injuries or injuries caused by insects, birds and man himself, through cultural practices.

This disease becomes important for passion fruit cultivation because, after harvest, the susceptibility of the fruits to rot is high, with a significant occurrence of loss of fresh mass and fermentation of the pulp. It is known that, for good acceptance by consumers, the fruits must have a yellow, smooth or slightly wrinkled skin and be free of stains and defects that could affect the quality of the pulp, such as cracks, presence of fungi and signs of attack by insects. The industry does not require aesthetic quality of fruits for juice processing.

Epidemiology

Passion fruit post-harvest diseases, in most cases, originate in the field, a phase known as pre-harvest. Factors such as unfavorable climatic conditions for the crop, and incorrectly applied cultural and phytosanitary treatments favor post-harvest diseases.

The occurrence of black fruit rot due to Lasiodiplody is associated with water stress. Post-harvest, spread occurs through contact between diseased and healthy fruits, directly or indirectly, as well as those fallen on the ground or in infected tissues in the plant, such as stems and stalks.

The pathogen develops rapidly in clayey soils or impermeable subsoils with high humidity. The fungus develops fully at temperatures between 12°C and 25°C. Lasiodiplody theobromae (Pat.) is a typical pathogen of tropical and subtropical regions, where it causes serious damage to numerous cultivated plant species, being considered a non-specialized parasite.

The pathogen is spread through wind, rain or irrigation when not managed properly. It penetrates the host tissue through wounds or natural openings, especially when the host plant is predisposed.

The fungus can survive on crop debris or remain quiescent on branches or lesions on the trunk. Favorable conditions for the occurrence of this disease are: high relative humidity (above 70%), dense plantings or periods with frequent rain and high temperatures (above 30ºC).

Symptoms

This fungus is not systemic, therefore, its infection is localized and progressive, destroying cell by cell, until it penetrates the interior of the plant organ. Symptoms only occur in ripe fruits or those in the process of maturing. Initially, small, light brown, rounded spots appear that come together and, at first, can be confused with anthracnose caused by Colletotrichum gloeosporioides.

Subsequently, these spots become dark, coalesce and tend to involve the entire fruit, which becomes dark and shriveled. The disease spreads quickly into the fruit, easily reaching the pulp, fermenting it and rotting the seeds.

In conditions of high humidity, the lesions become covered with the gray mycelium of the fungus and many pycnidia (resistance structures responsible for the dissemination of spores). It is a fast-growing fungus that generally causes fruit rot and mummification. Post-harvest, the disease is more severe at temperatures in the range of 25ºC to 30ºC and in conditions of high relative humidity.

Control

Preventive management of this disease has shown the best results, especially when larger spacings are adopted between rows of plants, providing greater aeration, avoiding planting in humid lowlands, as well as excess irrigation, so as not to create a microclimate favorable to the development of the pathogen.

Control must begin in the field, to reduce the source of inoculum and avoid damage to the fruits during handling, such as the adoption of integrated pre-harvest management practices. Post-harvest, alternative measures must be used to control these diseases, such as hydrothermal treatment and refrigeration.

Despite the lack of fungicides registered in Brazil for black fruit rot, there is information on the use of copper-based products, with applications mainly during the rainy season. Affected plants must have all fruits from the current bloom removed, ripe and green, affected or not, collecting those that have already fallen, in order to reduce the sources of inoculum in the cultivation area.

The passion fruit tree (box)

Originally from Tropical America, the passion fruit tree has adapted very well to environmental conditions from Brazil, which is currently the world's largest producer and consumer. Fruit growing is one of the most attractive investments in Brazilian agriculture, due to the country's favorable climate conditions, allowing fruit production throughout the year and income generation in relatively small areas, mainly through family farming.

Passion fruit cultivation has occupied a prominent position in Brazilian fruit growing, even when compared to other tropical fruits with a greater tradition of consumption. The nutritional quality of its fruits is of great importance, as they are rich in minerals and vitamins. The juice extracted from the fruits has a pleasant aroma and flavor, and is very well accepted in different markets.

In Brazil, more than 60% of domestic production is destined for consumption in natura and the remainder to the pulp and juice processing industries. As for social aspects, it plays an important role in regions where culture is explored, characterized by being an activity predominantly carried out on small properties and family labor.