Novel QTL for lodging resistance, PRL4, improves physical properties with high non-structural carbohydrate accumulation of basal culms in rice (Oryza sativa L.)

Resistance to lodging, an important problem in rice production, has three types: low plant height, strong culm, and high strength of the lower part of the plant. The determinants of strength of the lower part remains unclear, compared with plant height and culm strength. This study identified a new genetic factor involved in the strength of the lower part, as assessed by pushing resistance, using chromosomal segment substitution lines (CSSLs) to clarify the determinants of strength of the lower part by functional analysis of the CSSL and the introgression line (IL) harboring the identified quantitative trait locus (QTL). QTL analysis identified the QTL for increasing pushing resistance on chromosome 4, PRL4, which was not related to days to heading. The CSSL with PRL4 showed increased pushing resistance and physical strength of the basal culm, but decreased filled grain ratio and grain weight. The IL with PRL4, developed by backcrossing this CSSL, improved pushing resistance and the strain of culm until breaking under compression, and did not decrease yield traits. These lines with PRL4 increased the accumulation of non-structural carbohydrate (NSC) in the basal culm at the fully ripe stage. Thus, the genetic control of NSC accumulation in culms by PRL4 may improve the strength of the lower part by enhancing culm toughness with strength and ductility.