Genetic Dissection of Stem Internode Length and Its Effects in Wheat Based on a Genome-Wide Association Study

Plant height is a key agronomic trait in wheat that influences both yield potential and lodging resistance. It is primarily determined by the elongation of stem internodes. This study aimed to systematically evaluate the internode lengths of 224 Sichuan wheat cultivars, identify stable quantitative trait loci (QTL) regulating internode length and clarify their effects on agronomic traits, and screen the underlying candidate genes, thus providing important genetic resources and a theoretical basis for the targeted breeding of high-yield wheat varieties.

The lengths of the first (IL1), the second (IL2), and the third (IL3) internodes were measured under two different environments. The panel was genotyped using the wheat 120K SNP array. A genome-wide association study (GWAS) was employed to identify QTL regulating internode length. The phenotyping data was used for correlation analysis and the interpretation of the genetic effects of major QTL. The candidate genes of the major QTL were predicted based on wheat omics data.

Phenotypic analysis revealed continuous variation for all internode traits, with high broad-sense heritability estimates ranging from 75% to 89%. Correlation analysis showed that lengths of all three internodes were positively correlated with final plant height, with IL1 exhibiting the strongest correlation. Furthermore, IL2 and IL3 were highly correlated with each other, suggesting coordinated genetic regulation of the lower stem internodes. GWAS detected four stable QTLs on chromosomes 5A and 4D, namely QIL1.sau.5A for IL1, two tightly linked but distinct QTL QIL2.sau.5A.1 and QIL2.sau.5A.2 for IL2, and QIL3.sau.4D for IL3, respectively. Pleiotropy analysis demonstrated that QIL2.sau.5A.1 significantly increased plant height and spike length, while QIL3.sau.4D primarily promoted internode elongation and overall plant height. Based on functional annotation and spatiotemporal expression data, five candidate genes potentially involved in transcriptional regulation, hormone signal transduction, and cell growth were identified.

This study elucidated the genetic architecture of internode elongation in a panel of Sichuan wheat cultivars and identified two novel QTLs and several pleiotropic loci. These stable QTLs and the underlying candidate genes provided valuable resources for molecular marker-assisted selection aiming at optimizing plant height, improving lodging resistance, and enhancing yield potential in wheat.