“JJ603Balck” is a mid-late maturing high-yielding black rice having multiple-disease resistance. It was developed to increase the yield and disease resistance of Korean black rice. “JJ603Black” was derived from a cross between “Heughyang” and BC₂F₁ plants (Hopum*3/SR30075-1-12-6-1-1-1). “Heughyang” is a mid-late black rice with a short culm, while “Hopum” is a mid-late maturing rice cultivar with high yields and premium quality, and “SR30075” is a pyramid line carrying three bacterial blight resistance genes. “JJ603Black” was selected through the pedigree method, yield trials, and local adaptability tests, with a high selection pressure for black pericarp, resistance to bacterial blight K3a race, and high yield performance. The heading date of “JJ603Black” was August 19, 8 d later than that of “Heugnam,” which is the standard cultivar for black rice. “JJ603Black” is a cultivar tolerant to lodging with erect plant architecture. It showed multiple-disease resistance against bacterial blight and rice stripe virus owing to introgression resistance genes, Xa3+Xa21+Stvb-I; moreover, its yielding performance was high. The average brown rice yield of "JJ603Black" from 2016 to 2018 was 6.02 MT/ha, which was 14% more than that of “Heugnam” (5.30 metric/ha). Further, the anthocyanin content of “JJ603Black” (58 mg/100 g) was higher than that of “Heugnam” (51 mg/100 g). Therefore, “JJ603Black,” a high-yielding black rice cultivar with multiple-disease resistance, can be utilized for enhancing the disease resistance and yield of Korean black rice (Registration No. 7274).

The cultivation of early maturing rice in the plain areas in Korea is increasingly diversifying its cropping systems. Early maturing rice cultivars are usually vulnerable to bacterial blight (BB) and rice stripe virus (RSV) compared to mid- and mid-late maturing rice cultivars. To enhance the resistance of early maturing rice against BB and RSV, ‘IS592BB’ was developed by introgression of resistance genes, Xa3, Xa21, and Stvb-i into the genetic background of ‘Unkwang’, an early maturing rice cultivar with excellent agronomic characteristics. ‘IS592BB’ was derived from a backcross between ‘Unkwang’ and the F1 cross between ‘Unkwang’ and ‘SR31206-12’ (‘Unkwang’/‘SR30075’) and selected through the pedigree method, yield trials, and local adaptability tests. Using bioassay and marker-assisted selection to BB and RSV, Xa3, Xa21, and Stvb-i were pyramided in ‘IS592BB’. ‘IS592BB’ exhibited high-level and broad-spectrum resistance against BB, including the K3a race, the most virulent race in Korea, and also showed a resistance reaction to RSV. ‘IS592BB’ was found to be an early maturing rice cultivar with similar agronomic characteristics to ‘Unkwang’ such as early maturing, lodging tolerance with short culm, erect plant architecture, blast resistance, and high-yielding performance. In the genetic background analysis using 771 KASP (Kompetitive Allele-Specific PCR) markers, ‘IS592BB’ was confirmed to be the near-isogenic line (NIL) of ‘Unkwang’ with a 93.6% recovery rate. ‘IS592BB’ was successfully introgressed with the Xa3+Xa21+Stvb-i genes into ‘Unkwang’ without linkage drag negatively affecting its agronomic characteristics. ‘IS592BB’ would enhance the adaptability of early maturing rice in the plain area through its multiple disease resistance (Registration No. 7648).

Rice stripe virus (RSV) is one of the major constraints in rice production which is transmitted by the small brown plant hopper, Laodelphax striatellus. Identifying new resistance genes from diverse sources is important for rice breeding programs to enhance the resistance level and/or to overcome the breakdown of resistance genes. This study was conducted to identify novel sources of resistance against RSV. We used five RSV resistant varieties that do not harbor Stv-bⁱ. The presence of known genes for RSV resistance was identified using the InDel7 marker for Stv-bⁱ, two Indel (Sid primer set) markers for Stv-b, and DNA sequence analysis for OsSOT1. We revealed that two varieties, 02428 (IT236925) and Tung Ting Wan Hien 1, are novel RSV resistance sources.

This study was conducted to develop the early maturing rice lines with genes conferring resistance to bacterial blight and rice stripe virus to enhance the adaptability in plain area. Unkwang carrying Xa3 was used as a recurrent parent and SR30075 carrying Xa4+xa5+Xa21+Stvb-i was used as a donor parent. RL1(Resistant Line, BC₁F₇), RL2, RL3, RL4, and RL5(BC₂F₆) were bred through bio-assay of K3a race inoculation and phenotypic selection of agronomic traits. The presence of introduced genes was confirmed by testing the resistance levels against bacterial blight and rice stripe virus and then double-checked by using DNA marker. RL1 has all target genes, Xa3+xa5+Xa21+Stvb-i. RL2, RL3, and RL5 have Xa3+Xa21+Stvb-i whereas RL4 has only Xa21. Rice lines carrying Stvb-i showed resistance reaction to rice stripe virus. The combinations of bacterial blight resistant genes(Xa3+xa5+Xa21 and Xa3+Xa21) were found to be promising, as the rice lines carrying these genes enhanced a strong resistant reaction against 16 bacterial blight isolates. Also, the inoculation of K3a race did not alter the brown rice yield, ripened grain ratio and kernel quality of brown rice compared to control. Although RL1 containing all the target resistance genes showed excellent resistance performance, it is not suitable to cultivate in plain area due to instability to lodging, 80% yield level than Unkwang, and low grain quality. RL5 backcrossed twice with Unkwang was found to be a promising line due to its effective resistance gene combination, Xa3+Xa21+Stvb-i and good agronomic traits such as stability to lodging, higher yield and quality compared to Unkwang.