UNIVERSITY PARK, Pa. — Trichoderma species — a common fungus found in soils — have varying abilities to promote tomato plant growth and differentially affect the abundance of certain soil bacteria, according to a study led by researchers at Penn State.
The work was the latest in a line of research evaluating the use of this common group of fungi as an alternative to pesticides for controlling soilborne pathogens, said Seogchan Kang, professor in the College of Agricultural Sciences and co-corresponding author of the study.
Published in the journal The Microbe, the study also found that certain bacteria in the rhizosphere — the area of the soil directly surrounding the roots — may influence the plant growth-promoting ability of Trichoderma by affecting the fungus’s abundance and persistence in the soil.
Kang said the research is part of his lab’s efforts to help ensure the effectiveness, predictability and wide adoption of biological controls for fighting soilborne diseases as an alternative to pesticides.
“Certain fungi and bacteria not only protect plants from diseases but also enhance plant stress tolerance and growth,” Kang said. “Many studies have reported the successful use of such microbes as biological control agents, and some have been commercialized. However, their use has faced several hurdles and pitfalls, which have eroded confidence in using them among some growers.”
Farmers face multiple complex challenges that threaten the profitability and viability of their operations, the researchers said, which also threaten their ability to supply safe, nutritious and affordable food.
Ananda Y. Bandara, a researcher in the College of Agricultural Sciences and co-corresponding author, said the mitigation of threats like deleterious soilborne pathogens, while ensuring environmental stewardship, is one of the main challenges.
“These pathogens significantly decrease crop yields and quality, and increase costs of production by decreasing the efficiency of fertilizer, water, labor and fuel invested,” he said. “Fungicides help mitigate these threats, but a heavy reliance on fungicides not only increases the cost of production but also incurs ecological and human health-related costs.”
For more than a century, extensive research has been conducted to identify specific bacteria, fungi and insects that can help control pests and pathogens. However, these biological control agents have faced several hurdles, suggesting the need for more research and an improved understanding of why they do not perform well under certain conditions.
“For this study, we wanted to ask several questions,” Kang said. “When added to soil used for growing tomato plants, does the addition of different Trichoderma species differentially enhance plant growth? Do they affect the microbial communities associated with tomato roots and soil chemistry? And do any of these resulting changes potentially explain the mechanisms of Trichoderma-based biological control?”
For the study, the researchers collected topsoil from the Penn State Russell E. Larson Agricultural Research Center. A portion was autoclaved — a process that uses steam to sterilize the soil. Tomato seedlings were then placed in both types of soil.
Next, seedlings in each type of soil were split into four treatment groups: one that was treated with the Trichoderma species T. harzianum (Th), one treated with the species T. virens (Tv), one treated with both species (Tvh), and one treated with sterile water as a control.
Finally, the researchers analyzed how each treatment affected tomato growth and bacterial communities in the rhizosphere. They also assessed whether the volatile compounds emitted by these altered bacterial communities influence the growth of Trichoderma and Fusarium oxysporum, a soilborne fungal pathogen that affects many crop species, including tomato.
The researchers chose to focus on soilborne diseases, Kang said, because they threaten many critical crops but are challenging to detect and control early since they spread underground.
They found that Tv and Tvh expel bacteria in the rhizosphere in non-autoclaved soil, while partially restoring bacterial richness in the soil that had been autoclaved. The Tv and Tvh treatments also enhanced tomato growth in both types of soil, significantly increasing the average weight of shoots.
Additional studies could focus on examining the feasibility of using Trichoderma to restore bacterial diversity in soils after natural or human-mediated disturbances, the researchers said.
“Our findings also indicated that certain types of soil bacteria may influence Trichoderma abundance and persistence, which could help explain their inconsistencies in promoting crop growth and biocontrol efficacy at larger scales,” Bandara said.
Future efforts, including using machine learning with soil microbiome data from different soils, could help predict the environments where Trichoderma is most likely to deliver the expected benefits.
The U.S. Department of Agriculture's National Institute of Food and Agriculture helped support this research.