Landraces of temperate japonica rice have superior alleles for improving culm strength associated with lodging resistance.

Lodging can reduce grain yield and quality in cereal crops including rice (Oryza sativa L.). To achieve both high biomass production and lodging resistance, the breeding of new cultivars with strong culms is a promising strategy. However, little is known about the diversity of culm strength in temperate japonica rice and underlying genetic factors. Here, we report a wide variation of culm strength among 135 temperate japonica cultivars, and some landraces having the strongest culms among these cultivars. The genome-wide association study (GWAS) identified 55 quantitative trait loci for culm strength and morphological traits, and revealed several candidate genes. The superior allele of candidate gene for culm thickness, OsRLCK191, was found in many landraces but had not inherited to the modern improved cultivars. Our results suggest that landraces of temperate japonica rice have unutilized superior alleles for contributing future improvements of culm strength and lodging resistance.