Development of Blast-Resistant Rice Multiline Cultivars and Their Stability to Blast Resistance and Yield Performance

To ensure the durability of resistance to blast disease in high-quality japonica rice a long-term rice breeding project to develop a few blast-resistant multiline cultivars was carried out from 1987 to 1999. Seven resistance donors were selected based on the reaction to 10 races of blast fungus (Pyricularia grisea) through artificial infection test. Two high-quality japonica rice cultivars, Chucheongbyeo and Suweon 345 were used as recurrent parent. Four resistance genes conferring resistance to four dominant blast races, KJ-101, KJ-201, KJ-301 and KI-313 were targeted to introduce from selected donors into the recurrent parents. Several isogenic lines of two recurrent parents were developed through the selection of target resistance genes by artificially isolated infection of four blast fungus isolates and five to six times subsequent backcrossing during 1988-1993. Finally, twelve promising isogenic lines, consisted of two sets of six isogenic lines derived from backcross populations of two recurrent parents, were selected and were combined into four multiline rices. Each multiline rice was mixed with three isogenic lines according to the resistance reaction to four target fungus races and phenotypic similarity with recurrent parents. Field trials in hotspot farmer’s field (1994-1996) and local adaptability test at four locations (1997-1999) was performed for blast-resistant multiline rices. Although the finally selected promising isogenic lines revealed similar agronomic characteristics to the respective recurrent parents, they showed diverse reactions to ten blast fungus races. The selected isogenic lines of Suweon 345 exhibited not only the relatively wider spectrum of race-specific resistance but also a wider range of leaf blast resistance in the blast nursery test at two sites as compared with those of Chucheongbyeo. All multiline rices of both Suweon 345 and Chucheongbyeo revealed markedly less incidence of leaf or neck blast as compared with the recurrent parents. Although Suweon 345 multilines showed less infection of leaf blast in nursery bed and in farmer’s field than Chucheongbyeo multilines, the former showed more sever neck blast infection and less suppression effect on both leaf and neck blast occurrence in blast-hotspot field than the latter. Due to the markedly lower incidence of neck blast, a Chucheongbyeo multiline obtained 15% significantly higher grain yield than its original recurrent parent in blast hotspot field. This significant difference between two multiline cultivars in the suppression effect on blast disease incidence may be due to different level of field resistance between the two recurrent parents. This indicates that the field resistance should be equipped with the genetic background of recurrent parent to ensure the durability in blast resistance of multiline rice cultivars.