Advances in plant molecular techniques have dramatically widened the applicability of gene identification and pyramiding valuable genes. This study was carried out to pyramid five resistance genes for biotic stress into the japonica rice cultivar using marker-assisted selection (MAS) and marker-assisted background analysis of selected progenies using SSR markers. The Pi40, Xa4, xa5, Xa21 and Bph18 genes were combined in Jinbubyeo, a Korean japonica rice variety using MAS. Gene specific co-dominant PCR-based markers were used to select for homozygous recombinant lines in a segregating population derived from a cross between the parental homozygous resistant gene introgression lines. We had successfully developed multiple gene pyramided breeding lines (GPLs) for bacterial blight, blast, and brown planthopper using MAS in rice. The GPLs exhibited high resistance against biotic stress and had around 93% of the genetic background of the recurrent parent Jinbubyeo based on SSR graphical mapping. The yield and agronomic traits of the GPLs were similar to those of the recurrent parent, indicating that there is no apparent agronomic trait penalty associated with the presence of the resistance genes. The strategy of simultaneous foreground and phenotypic selection to introduce multiple R genes is very useful to reduce the cost and the time required for the isolation of desirable recombinants with target resistance genes in rice. The GPLs could be useful to enhance effective resistance for biotic stress and produce stable grain yield in japonica rice breeding programs.

Rice stripe virus (RSV) is a viral disease that seriously impacts rice production in East Asia, most notably in Korea, China, and Japan. Highly RSV-resistant transgenic japonica rice plants were generated using a dsRNAi construct designed to silence the entire sequence region of the RSV-CP gene. Transgenic rice plants were inoculated with a population of viruliferous insects, small brown planthoppers (SBPH), and their resistance was evaluated using ELISA and an infection rate assay. A correlation between the expression of the RSV-CP homologous small RNAs and the RSV resistance of the transgenic rice lines was discovered. These plants were also analyzed by comparing the expression pattern of invading viral genes, small RNA production and the stable transmission of the RSV resistance trait to the T3 generation. Furthermore, the agronomic trait was stably transmitted to the T4 generation of transgenic plants.

Anmi' is a new BPH (Brown planthopper) resistant japonica rice cultivar possessing the Bph18 gene derived from wild rice, Oryza australiensis and high yield potential with good grain quality. 'Anmi' was derived from a cross 'Junam' and 'IR65482-7-216-1-2' by a molecular marker assisted backcross breeding. The introgression line 'IR65482-7-216-1-2', the source of the Bph18 gene, was used as the donor parent for BPH resistance and 'Junam', a BPH-susceptible elite japonica cultivar with good grain quality, was used as the recurrent parent. 'Anmi' was developed by three times backcross the F1 plants with 'Junam'. The heading date of 'Anmi' is August 15 in central plain area, which is 5 days later than that of 'Hwaseong'. It has 77 cm in culm length, 21 cm in panicle length. The number of spikelets per panicle is more than that of 'Hwaseong' and 1,000 grain-weight of brown rice is 22.1 g which is less than 22.7 g of 'Hwaseong'. Milled rice kernel of 'Anmi' is clear in appearance, low in amylase content and excellent in palatability of cooked rice. 'Anmi' shows resistance to BPH, leaf blast disease, bacterial blight, rice stripe disease but susceptible to other virus disease and insect pest. The milled rice yield performance of 'Anmi' is about 5.76 MT/ha in local adaptability test for three years. This cultivar is adaptable to central plain area of Korea.

Samkwang1," a japonica rice variety, was developed as a cross between "Samkwang" and F1 of Suwon152 (IT008283), which has a medium maturing and lodging resistance and Samkwang (IT284608), a high quality variety with bacterial blight resistance and mid-late maturing property by the rice breeding team at NICS in 2015. The heading date of "Samkwang1" was August 8 in the middle plain area, which was 2 days early than that of "Hwaseong." "Samkwang1" had a culm length of 77 cm, which was 7 cm shorter than that of "Hwaseong," and it had 128 spikelets per panicle. The viviparous germination rate of "Samkwang1" was 2.1%. "Samkwang1" showed resistance to blast, bacterial blight (K1, K2, and K3 race) and stripe virus, but was susceptible to the K3a race of bacterial blight, dwarf and black streak dwarf viruses, and plant hoppers. The milled rice of this variety exhibits translucent and medium short grains. The cooked rice grains of "Samkwang1" have an excellent palatability index (0.35) and lower protein content (6.2%) than that of "Hwaseong." The characteristics related to grain milling were better than those of "Hwaseong," especially the head rice milling recovery ratio and head rice ratio (94.2%). "Samkwang1" showed 5.62 MT/ha of milled rice productivity at 11 sites under ordinary cultivation conditions (Registration No. 6798).

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