1125. Tackling a New Threat: The "Old but New" Rice False Smut Disease

Rice false smut is one of the diseases in which yellow to dark green smut balls form on the rice panicles at harvest. It was first reported in India in 1878, and in Japan, it was confirmed by Takahashi (1896) to be caused by a type of fungus called Ustilaginoidea oryzae. In recent years, the area affected by this disease in Japan has been increasing, and in 2016, it was designated as a harmful disease by the Government.

Despite being a long-known disease, rice false smut has not attracted much global attention until recently. One reason is that its occurrence has been relatively low compared to other diseases, and its impact on yield has been minimal.

Additionally, the misconception among farmers that this disease indicates a "bountiful harvest" has led to it being overlooked. However, in recent years, the disease has been reported in major rice-producing regions worldwide, across six continents and 59 countries, including tropical Africa, Asia, Australia, Oceania, Europe, and the Americas. This spread is attributed to the cultivation of high-yielding or hybrid varieties that are more susceptible to the disease, excessive use of nitrogen fertilizers to increase yield, and weather changes that bring more rain during the flowering and ripening stages, along with cooler, more humid conditions. Infections have been reported to reduce yield by up to 70%. Additionally, rice infected by this disease becomes discolored, and contaminated grains are considered substandard, significantly lowering their market value. Furthermore, the mycotoxins produced by the fungi are reported to be harmful to both animals and plants.

To ensure stable productivity and provide high-quality and food-safety rice, it is necessary to prevent and control the spread of this disease. In Japan, the National Agriculture and Food Research Organization (NARO) has been leading efforts to develop integrated control measures, and a control manual was published by Ashizawa in 2018. However, on a global scale, this disease has been treated as a minor issue, and thus, little research has been conducted so far.

In response to this situation, the International Rice Research Institute (IRRI) organized the inaugural international workshop on rice false smut, held from October 14 to 17, 2024. A total of 65 researchers from 35 institutions across 15 countries gathered, establishing an international rice false smut consortium (IRFSC) for collaborative research on rice false smut. The consortium aims to elucidate the infection mechanisms, develop resistant rice varieties, establish standard evaluation methods, and provide capacity-building support for developing countries. The workshop not only covered reports on the global infection status and research efforts but also featured demonstrations of artificial inoculation tests and presentations on the latest infection mechanisms. Additionally, there were discussions on infection mechanisms of other diseases, evolutionary genomics research, and predictive disease models, leading to a lively debate among countries with diverse perspectives on controlling this disease.

The Japan International Research Center for Agricultural Sciences (JIRCAS) has long collaborated with IRRI on rice research and has been involved in developing an international standard differential system for rice blast. Since 2006, JIRCAS has led an international research network project on rice blast, promoting the spread and education of the standard differential system and supporting the development of resistant varieties. Based on this experience, JIRCAS stressed the importance of establishing international cooperation and standardized protocols without borders as well as infectious diseases.

The newly established international research consortium plans to hold regular research meetings and disseminate information on the identification of resistance genes and evaluation methods. Research on the "old but new" rice false smut disease has only just begun. It is hoped that many researchers from the world will participate in this consortium and contribute to research that prepares for future threats.
 

Contributor: SAITO Hiroki, Tropical Agriculture Research Front (TARF)