In a recent investigation, scientists explored the relationships between *Pyricularia oryzae*, the fungus that causes rice blast, and the helpful soil bacterium *Streptomyces griseus*. Their research revealed that *P. oryzae* raised the pH level of its growth environment, which supported the growth of *S. griseus* even without any direct contact. These results emphasize the significance of interactions among soil microbes, guiding the development of environmentally friendly biological control methods for plant diseases.
Rice is a key food source for over half of the world’s population, making its cultivation vital for food security. Yet, the rice blast fungus Pyricularia oryzae (also known as Magnaporthe oryzae) poses a major risk to rice production, causing severe damage and significant yield losses. Conventional methods for controlling this pathogen frequently depend on chemical fungicides, which can harm the environment and lead to the emergence of resistant strains. As a result, researchers are increasingly investigating alternative methods that utilize natural microbial interactions to enhance plant health and manage diseases in a sustainable manner.
A study led by Assistant Professor Yuuki Furuyama from the Department of Applied Biological Science at Tokyo University of Science (TUS) sought to examine the relationship between P. oryzae and the advantageous soil bacterium Streptomyces griseus. The research team comprised Ms. Risa Sugiura, Prof. Kouji Kuramochi, Prof. Takashi Kamakura, and Dr. Takayuki Arazoe, all affiliated with TUS, along with Dr. Takayuki Motoyama from the Institute of Physical and Chemical Research and Dr. Hiroyuki Osada from the Institute of Microbial Chemistry. Their findings were published on September 23, 2024, in Environmental Microbiology Reports.
“Although a lot of research has been done on how rice blast fungi attack rice plants, many parts of their life cycle are still not well understood. Our study intends to shed light on the interactions between rice blast fungi and other soil microorganisms, looking at important aspects of their life cycle beyond just the infection phase,” Dr. Furuyama explains. To examine these interactions, the team carried out a set of experiments involving the co-cultivation of *P. oryzae* and *S. griseus*. They measured changes in pH levels in the growth medium and monitored the effects on the growth of *S. griseus* under different conditions.
The results demonstrated that the presence of *P. oryzae* significantly elevated the pH of the medium, which subsequently enhanced the growth of *S. griseus*. Remarkably, this increase in growth was not dependent on physical contact between the two microbes, suggesting that *P. oryzae* released non-volatile alkaline compounds causing this effect.
Moreover, the study indicated that other pathogenic fungi, such as *Fusarium oxysporum* and *Cordyceps tenuipes*, did not trigger similar growth in *S. griseus*, implying that the interaction identified is specific to *P. oryzae*. The researchers also excluded ammonia as the cause of the pH increase, leading them to hypothesize that polyamines produced by *P. oryzae* might be responsible for promoting growth.
The discovery of this unique microbial relationship has important implications for sustainable farming. *S. griseus* is known for producing antibiotics that can inhibit the growth of harmful microorganisms. By fostering the growth of *S. griseus*, *P. oryzae* might unintentionally create conditions that can be utilized to control its own proliferation. “Our findings suggest that *S. griseus* could serve as a biocontrol agent in rice fields, providing an alternative to chemical fungicides,” asserts Dr. Furuyama. “By encouraging the growth of *S. griseus* in rice paddies, we may be able to mitigate the impact of rice blast in an environmentally responsible manner,” Dr. Furuyama adds.
Furthermore, the study provides important insights into the ecological role of *P. oryzae*, suggesting that this fungus may affect the composition and dynamics of microbial communities in the soil. The researchers believe that their discoveries could have wider implications for understanding how pH changes influence microbial interactions, potentially leading to innovative biocontrol methods for other plant diseases as well.
With this groundbreaking discovery, the team has made significant progress toward achieving more sustainable agricultural practices. The potential to leverage microbial interactions to combat rice blast could transform disease management approaches in rice cultivation, offering hope for a future less reliant on harmful chemical solutions.
