Genetic Background-Dependent Expression and Interaction of Lr34, Lr46 and Lr67 in Wheat (Triticum aestivum L.) Reveal Distinct Modes of Adult Plant Resistance

Adult plant resistance (APR) is widely used in wheat breeding, but its behaviour across genetic backgrounds remains poorly understood. In this study, we analysed the ex-pression of three APR loci (Lr34, Lr46, Lr67) following their introgression into elite winter wheat cultivars. BC2F1 populations derived from crosses between donor lines and com-mercial cultivars were evaluated under controlled infection with Puccinia triticina. Gene expression was assessed using RT-qPCR, and miRNA abundance was quantified by ddPCR at five time points (0–48 h post-inoculation). Expression patterns differed markedly between genetic backgrounds, affecting both the magnitude and timing of gene activity. Lr34 and Lr67 showed the highest expression prior to inoculation, with no consistent or sustained induction following infection. In contrast, the candidate gene Lr46-Glu2 displayed a clear tendency towards early induction, with peak expression typically observed at 6–12 h post-inoculation, although the amplitude of this response varied among genotypes. Levels of miRNA varied across genotypes and time points and did not consistently reflect mRNA expression, indicating additional layers of post-transcriptional regulation. The results indicate that APR loci do not operate as isolated genetic determinants, but as components of a background-dependent regulatory system. Distinct temporal expression patterns suggest that Lr34 and Lr67 contribute to constitutive defence layers, whereas Lr46 represents an inducible early-response component. These findings highlight the importance of genetic context in shaping APR gene behaviour and provide a framework for the effective deployment of durable resistance in wheat breeding.