Increasing the lodging resistance of rice through genetic improvement has been an important target in breeding. To further enhance the lodging resistance of high-yielding rice varieties amidst climate change, it is necessary to not only shorten culms but strengthen them as well. A landrace rice variety, Omachi, which was established more than 100 years ago, has the largest culm diameter and bending moment at breaking in the basal internodes among 135 temperate japonica accessions. Using unused alleles in such a landrace is an effective way to strengthen the culm. In this study, we performed quantitative trait locus (QTL) analysis to identify the genetic factors of culm strength of Omachi using recombinant inbred lines (RILs) derived from a cross between Omachi and Koshihikari, a standard variety in Japan. We identified three QTLs for the culm diameter of the 5th internode on chromosomes 3 (qCD3) and 7 (qCD7-1, qCD7-2). Among them, qCD7-2 was verified by QTL analysis using the F₂ population derived from a cross between one of the RILs and Koshihikari. RNA-seq analysis of shoot apex raised 10 candidate genes underlying the region of qCD7-2. The increase in culm strength by accumulating Omachi alleles of qCD3, qCD7-1 and qCD7-2 was 25.0% in 2020. These QTLs for culm diameter pleiotropically increased spikelet number per panicle but did not affect days to heading or culm length. These results suggest that the Omachi alleles of qCD3, qCD7-1 and qCD7-2 are useful for breeding to increase lodging resistance and yield.

通过遗传改良提高水稻的抗倒伏性一直是育种的重要目标。为进一步增强高产水稻品种在气候变化中的抗倒伏能力，不仅要缩短茎秆，还要加强茎秆。建立于 100 多年前的地方品种大町在 135 种温带粳稻中具有最大的茎直径和基部节间折断弯矩加入。在这样的地方品种中使用未使用的等位基因是加强茎秆的有效方法。在这项研究中，我们进行了数量性状基因座 (QTL) 分析，使用源自日本标准品种 Omachi 和 Koshihikari 杂交的重组自交系 (RIL) 来鉴定 Omachi 茎秆强度的遗传因子。我们在 3 号染色体 ( qCD3 ) 和 7 号染色体 ( qCD7-1 , qCD7-2 )上鉴定了第 5 个节间的茎杆直径的三个 QTL 。其中，qCD7-2通过使用来自RIL之一和Koshihikari之间的杂交的F ₂群体的QTL分析来验证。茎尖的 RNA-seq 分析提出了qCD7-2区域下的 10 个候选基因. 2020 年，通过积累qCD3、qCD7-1和qCD7-2的 Omachi 等位基因，茎秆强度增加了25.0%。这些茎秆直径 QTL 多效地增加了每穗的小穗数，但不影响抽穗天数或茎秆长度。这些结果表明qCD3、qCD7-1和qCD7-2的 Omachi 等位基因可用于育种以增加抗倒伏性和产量。