Pyramiding of multiple strong-culm genes originating from indica and tropical japonica to the temperate japonica rice

Severe lodging has recurrently occurred at strong typhoon’s hitting in recent climate change. The identification of quantitative trait loci and their responsible genes associated with a strong culm and their pyramiding are important for developing high-yielding varieties with a superior lodging resistance. To evaluate the effects of four strong-culm genes on lodging resistance, the temperate japonica near isogenic line (NIL) with the introgressed SCM1 or SCM2 locus of the indica variety, Habataki and the other NIL with the introgeressed SCM3 or SCM4 locus of the tropical japonica variety, Chugoku 117 were developed. Then, we developed the pyramiding lines with double,triple and quadruple combinations derived from step-by-step crosses among NIL-SCM1–NIL-SCM4. Quadruple pyramiding line (NIL-SCM1 + 2 + 3 + 4) showed the largest culm diameter and the highest culm strength among the combinations and increased spikelet number due to the pleiotropic effects of these genes. Pyramiding of strong culm genes resulted in much increased culm thickness, culm strength and spikelet number due to their additive effect. SCM1 mainly contributed to enhance their pyramiding effect. These results in this study suggest the importance of identifying the combinations of superior alleles of strong culm genes among natural variation and pyramiding these genes for improving high-yielding varieties with a superior lodging resistance.