Temperate japonica rice is mainly cultivated in temperate regions. Many temperate japonica varieties have a superior grain quality that is preferred in Northeast Asian countries such as Japan, Korea, and China. The changes in consumers’ preferences in Southeast Asia and Western countries has contributed to increasing the demand for temperate japonica. Most temperate japonica varieties developed in temperate regions typically exhibit extra-early flowering under the short-day conditions in the tropics, which usually results in severely reduced yields. Since 1992, we have been developing temperate japonica varieties that can adapt to tropical environments to meet the increasing demand for temperate japonica rice, having released six varieties in the Philippines. Especially, the yield of one of the temperate japonica varieties, Japonica 7, was comparable to the yields of leading indica varieties in the Philippines. Here, we discuss the current breeding initiatives and future plans for the development of tropical-region-bred temperate japonica rice.

The Rural Development Administration (RDA) of the Republic of Korea, in collaboration with International Rice Research Institute (IRRI), developed six temperate japonica rice varieties—MS11, Japonica 1, 2, 6, 7, and Cordillera 4—which were officially approved for release in tropical environments. These varieties offer improved eating quality, enhanced lodging resistance, and increased market value. Although initial evaluations indicated that the varieties were resistant to moderately resistant to major biotic stresses, recent field trials revealed a gradual increase in susceptibility over time. To address this, we conducted comprehensive evaluations of these varieties against rice blast under both greenhouse and field conditions and assessed their responses to bacterial leaf blight (BLB), rice tungro spherical virus (RTSV), and brown planthopper (BPH) under controlled environments. Additionally, whole-genome sequencing was employed to confirm the presence of known resistance alleles. Our findings revealed variable resistance profiles across the six varieties. Japonica 1 exhibited the most stable resistance to blast, supported by the presence of the Pi5 allele. Japonica 7 showed strong resistance to key BLB isolates and moderate resistance to a broader range of Xoo races, supported by the resistant Xa25/OsSWEET13 haplotype. In addition, Japonica 7, along with Japonica 6, carried the tsv1 gene for RTSV resistance. However, none of the six varieties possessed other major resistance genes for BPH. These results highlight the urgent need to introgress durable resistance genes into tropical japonica rice to enhance resilience and broaden the spectrum of biotic stress resistance—critical traits for sustainable rice production in tropical environments.