Sumin Jo

Research on tongil-type rice has aimed to enhance genetic diversity and yield through indica-japonica hybridization; however, poor eating quality remains a limitation in Korea. We evaluated three high-yielding tongil-type waxy cultivars, focusing on the allelic variation in the granule-bound starch synthase I (GBSSI) gene and its effects on quality traits. Physicochemical properties, including texture and retrogradation, were assessed using a texture analyzer, and pasting properties were analyzed using a Rapid Visco Analyzer (RVA). ‘Hanareumchal’ showed the softest texture (1.70 Kgf) and the slowest retrogradation rate. Genetic analysis revealed a unique Wx-g2 allele derived from Japanese waxy rice (‘Odorokimochi’), which likely underlies these favorable traits. RVA profiling further indicated reduced viscosity parameters, supporting its suitability for processed rice products that require extended shelf life and texture stability. These findings highlight the role of Wx-g2 in improving tongil-type waxy rice and provide useful insights for breeding programs targeting enhanced processing performance.

Seong-Gyu Jang, Ji-Yoon Lee, Ju-Won Kang, Youngho Kwon, So-Myeong Lee, Sais-Beul Lee, Jun-Hyeon Cho, Dong-Soo Park, Jong-Hee Lee, Soon-Wook Kwon, and Sumin Jo. Korean J. Breed. Sci. 2024;56:225-35. https://doi.org/10.9787/KJBS.2024.56.3.225

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.

Bakanae disease is a fungal disease of rice (Oryza sativa L.) caused by the pathogen Gibberella fujikuroi (also known as Fusarium fujikuroi). This study was carried out to identify novel quantitative trait loci (QTLs) from an indica variety Zenith. We performed a QTL mapping using 180 F_2:9 recombinant inbred lines (RILs) derived from a cross between the resistant variety, Zenith, and the susceptible variety, Ilpum. A primary QTL study using the genotypes and phenotypes of the RILs indicated that the locus qBK1^z conferring bakanae disease resistance from the Zenith was located in a 2.8 Mb region bordered by the two RM (Rice Microsatellite) markers, RM1331 and RM3530 on chromosome 1. The log of odds (LOD) score of qBK1^z was 13.43, accounting for 30.9% of the total phenotypic variation. A finer localization of qBK1^z was delimited at an approximate 730 kb interval in the physical map between Chr01_1435908 (1.43 Mbp) and RM10116 (2.16 Mbp). Introducing qBK1^z or pyramiding with other previously identified QTLs could provide effective genetic control of bakanae disease in rice.

Chlorate resistance analysis is an effective approach commonly used to distinguish the genetic variation between Oryza sativa L. ssp. indica and japonica, and predict the nitrogen use efficiency (NUE). This study aimed at investigating the response of a doubled haploid (DH) population derived from anther culture of 93-11 × Milyang352 exposed to 0.1% potassium chlorate (KClO₃) at the seedling stage. The results revealed that the parental rice lines 93-11 (indica) and Milyang352 (japonica) showed distinctive phenotypic responses. The parental line 93-11 scored highly sensitive (0% survival) and Milyang352 scored resistant (66.7% survival) 7 days after treatment. The DH lines reflected the differential phenotypic response observed in parental lines. Interestingly, we identified a novel quantitative trait locus (QTL) for chlorate resistance on chromosome 3 (qCHR-3, 136 cM, logarithm of the odds—LOD: 4.1) using Kompetitive Allele-Specific PCR (KASP) markers. The additive effect (−11.97) and phenotypic variation explained (PVE; 14.9%) indicated that the allele from Milyang352 explained the observed phenotypic variation. In addition, shoot growth showed a significant difference between parental lines, but not root growth. Moreover, in silico analysis identified candidate genes with diverse and interesting molecular and physiological functions. Therefore, this study suggested that the QTL qCHR-3 harbors promising candidate genes that could play a role in the regulation of nitrogen metabolism in rice.

Bakanae disease is a fungal disease of rice ( Oryza sativa L.) caused by the pathogen Gibberella fujikuroi (also known as Fusarium fujikuroi ). Recently the disease incidence has increased in several Asian countries and continues to spread throughout the world. No rice varieties have been developed yet to be completely resistant to this disease. With increasing need to identify various genetic resources to impart resistance to local elite varieties, this study was carried out to identify novel quantitative trait loci (QTLs) from an indica variety Zenith. We performed a QTL mapping using 180 F _2:9 recombinant inbred lines (RILs) derived from a cross between the resistant variety, Zenith, and the susceptible variety, Ilpum. A primary QTL study using the genotypes and phenotypes of the RILs indicated that the locus qBK1 ^z conferring bakanae disease resistance from the Zenith was located in a 2.8 Mb region bordered by the two SSR markers, RM1331 and RM3530 on chromosome 1. The log of odds (LOD) score of qBK1 ^z was 13.43, accounting for 30.9% of the total phenotypic variation. A finer localization of qBK1 ^z was delimited at an approximate 730 kb interval in the physical map between Chr01_1435908 (1.43 Mbp) and RM10116 (2.16 Mbp). The development of a rice variety with a higher level of resistance against bakanae disease is a major challenge in many rice growing countries. Introducing qBK1 ^z or pyramiding with other previously identified QTLs could provide effective genetic control of bakanae disease in rice.