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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.

Physiological responses to salinity stress were evaluated in six rice genotypes differing in their tolerance to salinity at the seedling stage. Susceptible genotypes ('Dongjingbyeo', 'Hwayeongbyeo', and 'IR29') showed salt injury symptoms (mean 8.8) and higher visual score under salt stress than that of tolerant ones ('Pokkali', 'IR74009', and 'IR73571'). As salinity affects growth and physiological parameters, the six genotypes thus showed significant reduction because of salt stress. Tolerant Japonica/Indica bred lines ('IR74009', 'IR73571') showed lower reduction, 33.9%, 34.5%, and 50%, respectively, in plant seedling height, dry shoot weight and dry root weight than those of the susceptible Japonica varieties ('Dongjingbyeo', 'Hwayeongbyeo'), and the highest reduction under salt stress was observed in dry root weight, followed by dry shoot weight and seedling height, respectively. Shoot Na+ concentration of IR74099 and IR73571 was lower than that of the susceptible varieties, 'Dongjinbyeo' and 'Hwayeongbyeo'. There were no significant differences among genotypes in root Na+ concentration. Shoot K+ concentration showed a reverse tendency compared to shoot Na+ concentration. IR74009 and IR73571 had considerably lower ratio compared to 'Dongjinbyeo' and 'Hwayeongbyeo' in Na+/K+ ratio of their shoot and was not different the tolerant check, 'Pokkali'. [ABSTRACT FROM AUTHOR]

In order to identify the degree of salinity tolerance of the indica and japonica rice groups, 10 varieties were tested under saline and non-saline conditions. Twelve-day-old seedlings were grown in normal culture solution, then initially salinized at an electrical conductivity (EC) of 6 dS/m for 4 days, and finally salinized at an EC of 12 dS/m for the next 14 days. The growth parameters, and Na and K absorption in the shoot were measured to characterize the tolerance level of the two rice groups. Reduction in all growth parameters of tolerant varieties was significantly lower in indica varieties than in japonica varieties. Tolerant indica varieties were good Na excluders, absorbed high amounts of K, and maintained a low Na/K ratio in the shoot. Tolerant japonica varieties also absorbed less Na but were not as good excluders as indica varieties. Shoot K concentration alone did not show any relationship to salinity tolerance. These results indicate that, for all parameters measured, the tolerance level of indica was higher than that of japonica. [ABSTRACT FROM AUTHOR]

Near-isogenic lines (NILs) carrying bacterial blight resistance genes (Xa4, xa5 and Xa21) were developed in japonica rice using Suweon345 as genetic background. NILs were selected by gene specific DNA markers and inoculation of K1 or K3a race. NILs conferring Xa4 were resistant to K1, K2, K3, and moderately resistant to K3a. NILs conferring xa5 were resistant to K1, K2, K3, and K3a. NILs having Xa21 were susceptible to K1, while resistant to K2, K3 and K3a. Target genes of NILs with the genetic background of Suweon345 were also confirmed by using eleven Philippines races and International Rice Bacterial Blight (IRBB) NILs carrying Xa4, xa5 and Xa21. All NILs had no significant difference from their recurrent parents in the major agronomic traits except for panicle length and brown rice 1,000 grain weight. Heading date of NILs ranged from Aug. 10 to Aug. 11, which was similar to that of recurrent parent, Suweon345. Culm length, number of grains per panicle and ratio of ripened grain of NILs were similar to those of Suweon345. Milled rice of NILs was ranged from 4.82 to 4.93MT/ha. These NILs will be useful for improving resistance to K3a race of bacterial blight pathogens in Korean japonica cultivars. [ABSTRACT FROM AUTHOR]

'Honong' is a new japonica rice variety developed and registered by the rice breeding team of Department of Rice and Winter Cereal Crop, NICS, RDA in 2009. This variety was derived from mutagen MNU (N-methyl-N-nitrosourea) treatment on fertilized egg cells of Unbong31. This variety has about 126 days growth duration from transplanting to harvesting in west-southern coast, Honam and Youngnam plain of Korea. It has 79 cm in culm length and is tolerant to lodging. In reaction to biotic and abiotic stresses, it show resistance to blast, bacterial blight pathogen races from K1 to K3 and stripe virus, but susceptible to other major diseases and insect pests. The milled rice of 'Honong' exhibits translucent, relatively clear non-glutinous endosperm and medium short grain. It has higher amylose content (20.3%) and lower protein content (6.3%), and good palatability of cooked rice compared with Nampyeong. The milled rice yield performance of this variety is about 5.44MT/ha in local adaptability test for three years. 'Honong' would be adaptable to west-southern coast, Honam and Youngnam plain of Korea. [ABSTRACT FROM AUTHOR]

Salt tolerance was evaluated at the young seedling stage of rice (Oryza sativa L.) using recombinant inbred lines (MG RILs) from a cross between Milyang 23 (japonica/indica) and Gihobyeo (japonica). 22 of 164 MG RILs were classified as tolerant with visual scores of 3.5-5.0 in 0.7% NaCl. Interval mapping of QTLs related to salt tolerance was conducted on the basis of the visual scores at the young seedling stage. Two QTLs, qST1 and qST3, conferring salt tolerance, were detected on chromosome 1 and 3, respectively, and the total phenotypic variance explained by the two QTLs was 36.9% in the MG RIL population. qST1 was the major QTL explaining 27.8% of the total phenotypic variation. qST1 was flanked by Est12~RZ569A, and qST3 was flanked by RG179~RZ596. The detection of new QTLs associated with salt tolerance will provide important information for the functional analysis of rice salt tolerance. [ABSTRACT FROM AUTHOR]