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Bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo) is a destructive disease of rice in the major rice growing countries of Asia. In 2003, a serious bacterial blight epidemic occurred in the southwestern coastal areas in Korea, causing significant yield loss due to the emergence of a new race, K3a. IR24 near-isogenic lines containing Xa4, xa5, Xa7 and Xa21 genes conferred different degrees of resistance to the most virulent K3a isolate, HB01009 in an inoculation experiment in the greenhouse. Expression levels of the resistance genes, Xa4, xa5 and Xa21 were studied in two F2 populations derived from the crosses between elite japonica cultivars and an advanced backcross breeding line possessing Xa4, xa5 and Xa21 genes. F2 progenies segregated for K3a resistance (R) and susceptible (S) phenotypes in a ratio of 3(R):1(S) indicated that K3a resistance was controlled by a major dominant gene. Three PCR markers tightly linked to the resistance genes Xa4, xa5 and Xa21 confirmed the presence of the genes and their interaction with each gene. This study demonstrated that the Xa21 gene dominantly contributed to K3a resistance. However, the Xa4 gene also contributed to the full expression of resistance. The level of expression of strong resistance to K3a race was attributed to the presence of Xa21 and Xa4 genes irrespective of the presence of xa5 gene. Our results suggest that the R-gene combinations of Xa4+Xa21 could be a useful and effective strategy toward improving resistance to K3a race of Korean japonica cultivars.

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.

It is reported that the absence of lipoxygenase-3 (LOX-3) may contribute to a reduction in stale flavor after the storage of rice.To improve the quality of stored rice of the Korean japonica rice cultivar, we conducted a breeding program to develop near-isogenic rice without LOX-3 in the genetic background of Saenuri, a mega variety of Korea. In the first step of the breeding program, we used a donor parent of LOX-3 null, Daw Dam, and a recurrent japonica parent, Sindongjin, to develop HR27873-AC12 by backcross (BC1), color test for introgression of lox-3, and anther culture for rapid fixation. In the second step, we used the donor parent, HR27873-AC12, and the recurrent parent, Saenuri, to develop HR28896-31-3-1-1 by backcross (BC1), marker-assisted selection (MAS) for lox-3, and phenotypic selection (PS) for agronomic traits. Finally, in the third step, we developed HR30960-186-2-1-2-1 (Jeonju624), derived from a cross between Saenuri and HR28896-31-3-1-1, by MAS for lox-3 and PS with high selection pressure for agronomic characteristics. Jeonju624 was confirmed with the introgression of lox-3 by molecular marker. Jeonju624 was a mid-late maturing rice with similar agronomic characteristics to Saenuri, lodging tolerance with short culm, erect plant architecture, and resistance to bacterial blight and rice stripe virus. The yield components of Jeonju624 were mostly similar to Saenuri, except for the 1,000-grain weight of brown rice. The appearance of the grain of Jeonju624 was better than that of Saenuri, and the characteristics of cooked rice were similar to those of Saenuri. In the genetic background analysis using 406 KASP (Kompetitive Allele-Specific PCR) markers, Jeonju624 was confirmed to be the near-isogenic line (NIL) of Saenuri with a 95.8% recovery rate. Jeonju624 is the NIL of Saenuri without LOX-3, and overcomes the linkage drag of Daw Dam with similar agronomic characteristics and genetic background to Saenuri. Jeonju624 can be utilized as a practical cultivar to improve the quality of stored rice, breeding material for the introgression of lox-3, and genetic material to elucidate the effect of introgressed genes.

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