Threats to Japanese agriculture from newly emerged plant viruses and viroids

International trade is one of the main ways by which a species can expand its geographical range. Since the beginning of the twenty-first century, the worldwide distribution of many pests has increased through the international circulation of crop seeds and seedlings. In this review, viruses and viroids that have invaded Japan since 2000 are described in order of their prevalence. Measures to prevent invasion by such viruses and viroids and protect agricultural production in Japan from alien pests are discussed.