Molecular Pathogens 2024, Vol.15, No.4, 189-199 http://microbescipublisher.com/index.php/mp 190 This study provides a comprehensive overview of emerging viral and fungal viral threats in rice cultivation. It summarizes the current knowledge on the diversity, transmission, and impact of rice viruses and fungal viruses, explores the historical context and factors contributing to the emergence and spread of these pathogens, and discusses the implications of these threats for rice production and global food security. The study highlights recent scientific advances and identifies knowledge gaps that require further research. 2 Common Rice Viruses and Their Impacts 2.1 Identification of major viral pathogens affecting rice Rice cultivation is significantly threatened by various viral pathogens, which have been identified across different regions globally. Among the most notable are the southern rice black-streaked dwarf virus (SRBSDV) and rice black-streaked dwarf virus (RBSDV) in Asia, rice yellow mottle virus (RYMV) in Africa, and rice stripe necrosis virus (RSNV) in America. These viruses have been recorded since the late 19th century and continue to cause substantial damage to rice production. The rice gall dwarf virus (RGDV) and the recently discovered rice tiller inhibition virus (RTIV) also pose significant threats, with RTIV emerging from native wild rice habitats and causing low-tillering disease in cultivated rice (Yan et al., 2022; Yang, 2024). 2.2 Transmission pathways and vectors for rice viruses The transmission of rice viruses is predominantly facilitated by insect vectors, particularly planthoppers and leafhoppers. For instance, SRBSDV and RBSDV are transmitted by the white-backed planthopper (Sogatella furcifera), while RYMV is spread by various species of beetles (Figure 1) (Wang et al., 2022; Wu et al., 2022). The rice reoviruses, including SRBSDV, are transmitted in a persistent propagative manner by leafhoppers or planthoppers, which means the virus replicates within the vector and is transmitted throughout the vector's life. RTIV is transmitted by specific aphid vectors, highlighting the diverse range of insect vectors involved in the spread of rice viruses. The complex interactions between these viruses and their vectors involve evolutionary trade-offs that balance the fitness cost of viral infection in insects with the need for persistent transmission (Wei et al., 2018). Figure 1 The complex interactions between rice plants and viruses (Adopted from Wang et al., 2022) The transmission of rice viruses is closely related to their hijacking of host factors through viral proteins. Viruses are able to finely regulate processes, not only suppressing the host's defenses but also utilizing the host's resources for their own reproduction. Meanwhile, the host employs mechanisms such as RNA silencing to defend against viral infections, but viruses have their own strategies to overcome these defenses. This complex virus-host interaction mechanism is at the core of rice virus transmission and pathogenicity.
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