Fungi from the Caatinga show potential against agricultural diseases

A study conducted with fungi of the genus Trichoderma isolated from soils of the semi-arid Caatinga region revealed that native species of this biome possess important characteristics for the biological control of agricultural diseases, in addition to high thermal resistance and the ability to adapt to extreme environments.

Researchers investigated fungi collected from areas of native vegetation and irrigated melon crops in the states of Bahia and Piauí. In total, 14 isolates belonging to five different species of Trichoderma were identified: Trichoderma asperellum, Trichoderma asperelloides, Trichoderma koningiopsis, Trichoderma virens, and Trichoderma spirale. The results indicate that the composition of these microbial communities varies according to land use and the chemical characteristics of the environment.

The research reinforces that the Caatinga biome harbors a still largely unexplored microbial diversity, capable of providing organisms adapted to the adverse conditions of heat and water scarcity. These microorganisms could become important allies in the development of biofungicides aimed at sustainable agriculture in semi-arid regions. 

Semi-arid region under pressure

The Caatinga is the only exclusively Brazilian biome and is characterized by scarce and irregular rainfall, high temperatures, and vegetation adapted to drought. Even in adverse climatic conditions, irrigated agriculture has expanded strongly in the Northeast, including in the area covered by the biome, mainly for crops of high commercial value such as melon.

However, intensive cultivation favors the emergence of soil-borne diseases that are difficult to control. Fungi, such as Fusarium, Macrophomina, Rhizoctonia, and oomycetes—a class of filamentous microorganisms that resemble fungi—like Pythium cause root rots and vascular wilts, diseases that drastically reduce agricultural productivity.

According to Gabriel Mascarin, a researcher at Embrapa Meio Ambiente (SP) and one of the authors of the study, "understanding the ecological interactions of beneficial microorganisms with pathogens is fundamental to creating agricultural strategies that are less dependent on chemical fungicides and more resilient to climate change."

Microscopic warfare in the soil

Fungi of the genus Trichoderma are already known worldwide for their potential to control plant diseases. They act through different mechanisms: they compete for nutrients, parasitize other fungi, produce toxic substances against pathogens, and can even stimulate natural plant defense mechanisms, explains Wagner Bettiol, also a researcher at Embrapa Meio Ambiente.

In addition to biological control, several species of this genus promote plant growth and help plants withstand environmental stresses such as drought and salinity.

In the study, the researchers evaluated two main mechanisms of antagonism among isolates from the Caatinga: direct confrontation — involving competition and mycoparasitism, a phenomenon in which one fungus consumes another to obtain nutrients — and the production of volatile compounds capable of inhibiting the growth of pathogens even without physical contact.

The tests were conducted against five organisms that cause agricultural diseases: Fusarium sulawesiense, Fusarium solani, Macrophomina phaseolina, Rhizoctonia solani, and Pythium myriotylum.

Fungi adapted to heat

One of the research findings was that isolates from melon-growing areas showed greater heat tolerance than those found in native areas.

Scientists tested the growth of fungi at temperatures up to 40 °C. Although all grew similarly at 25 °C and 30 °C, significant differences emerged only at 35 °C. Thus, the study proved that isolates of Trichoderma asperellum, Trichoderma asperelloides, and Trichoderma virens originating from agricultural soils showed superior tolerance under thermal stress.

The authors interpret this result as a possible reflection of ecological adaptation to the irrigated agricultural environment of the semi-arid region, where high temperatures and thermal fluctuations are frequent.

This heat tolerance is considered a strategic characteristic for future agricultural bio-inputs, since many commercially used microorganisms lose effectiveness when applied in climatic regions different from those from which they were originally isolated.

Different strategies against each disease

In the case of agricultural diseases, laboratory tests revealed that biological control mechanisms varied according to the target pathogen.

Against Rhizoctonia solani and Macrophomina phaseolina, direct confrontation was more effective. In these cases, Trichoderma isolates grew rapidly on the pathogens, dominating their colonies through competition and parasitism.

Against Pythium myriotylum and Fusarium species, especially Fusarium solani, the volatile compounds produced by the fungi played a predominant role. In some cases, the compounds released by the isolates reduced pathogen growth by more than 70%. 

Researchers highlight that different Trichoderma species appear to use distinct strategies depending on the pest found in the soil. This reinforces the need to select specific strains for each agricultural system and type of disease.

Among all the isolates evaluated, Trichoderma koningiopsis stood out as the most promising. It showed consistent performance against all pathogens tested and in different antagonism mechanisms.

Other isolates, such as Trichoderma virens, have also demonstrated high antagonistic activity, although with less uniform results.

Spore production is an industrial challenge.

In addition to its effectiveness in biological control, the researchers also analyzed the ability to produce spores, reproductive cells also present in fungi, which are used in the manufacture of commercial biofungicides.

“This factor is crucial for enabling the large-scale production of biological products. In Brazil, most Trichoderma-based biofungicides are still produced through solid-state fermentation using cereal grains,” says Mascarin.

In the experiment, the fungi were cultivated in parboiled rice. The best spore producers were isolates belonging to the species Trichoderma asperelloides and Trichoderma asperellum, which reached more than 1,4 billion conidia (asexual spores produced by some fungi) per gram of substrate after ten days of cultivation.

On the other hand, some of the isolates most aggressive against pathogens showed low spore production, indicating that biological control efficiency and industrial productivity do not always go hand in hand.

According to the authors, this suggests that different species of Trichoderma invest energy in distinct ecological strategies: some prioritize competition and antagonism, while others exhibit greater reproductive capacity.

Soil influences microbial biodiversity

The research also demonstrated that soil chemical properties strongly influence the distribution of Trichoderma species. Researchers observed that Trichoderma virens and Trichoderma asperellum were associated with soils with higher fertility, phosphorus content, and organic matter.

Trichoderma spirale, on the other hand, appeared associated with more acidic soils rich in aluminum and iron, characteristics common in less managed natural environments. These results indicate that the microbial composition of the Caatinga is shaped by both natural conditions and agricultural practices, explains Rodrigo Mendes, a researcher at Embrapa Meio Ambiente.

Potential for resilient agriculture

The authors state that the results reinforce the importance of exploring Brazilian microbial biodiversity in search of agricultural solutions adapted to local conditions.

Biofungicides produced with microorganisms native to the Caatinga biome may exhibit greater survival, persistence, and efficiency in semi-arid environments than imported products or those developed for other climatic regions.

“Furthermore, the use of biological agents reduces dependence on synthetic fungicides and contributes to more sustainable agricultural systems,” comments Bettiol.

The researchers advocate, as next steps, conducting field tests, evaluating the ability of these fungi to colonize melon plants, and studying possible effects on plant growth and agricultural productivity.

They also suggest investigating the use of microbial consortia, combining different species or isolates of Trichoderma to enhance protection against diseases and increase plant resistance to water and heat stress.