Morphological Traits Associated with the Quantitative Trait Locus for Lodging Tolerance in Soybean

Lodging tolerance is an important trait of soybean [Glycine max (L.) Merr.] that affects yield stability and combine-harvesting efficiency. Previously, a quantitative trait locus analysis of lodging scores was performed using recombinant inbred lines developed by crossing the lodging-susceptible cultivar Toyomusume with the lodging-tolerant cultivar Toyoharuka, and the major quantitative trait locus qLS19-1 was identified. However, the morphological traits associated with qLS19-1 remain unclear. To develop high-precision DNA markers for qLS19-1, it is necessary to identify its associated lodging tolerance-related traits. Here, we studied the effects of qLS19-1 on lodging-related traits, primarily pushing resistance, using the Toyomusume-backcrossed line and near isogenic lines (NILs). The Toyoharuka allele at qLS19-1 may increase the number of primary lateral roots and cause a high pushing resistance, resulting in a lower ratio of the pushing resistance moment. The negative correlation between the number of primary lateral roots and the lodging scores in 2 yr suggests that this trait's influence on lodging score is stable. The numbers of primary lateral roots of six recombinant NILs were evaluated for the fine mapping of qLS19-1. Sat_099 and BARCSOYSSR_19_1255 were the molecular markers that correlated with changes in the number of primary lateral roots among the recombinant NILs. We believe that the gene responsible for controlling primary lateral root number is located within the associated 356-kb region. Thus, the investigation of the number of primary lateral roots and/or the marker-assisted selection for qLS19-1 may improve lodging tolerance in breeding programs.