In cucumber, rootstocks markedly influence scion resistance to powdery mildew; however, the divergence in resistance induced by different rootstocks and the underlying regulatory mechanisms remain poorly understood. In this study, the cucumber cultivar ‘Xintaimici’ was used as the scion and grafted onto pumpkin rootstocks ‘nd8’ (resistant) and ‘nd4’ (susceptible), generating resistant (C/R) and susceptible (C/S) graft combinations, with self-grafted plants (C/C) serving as the control. Following powdery mildew inoculation, disease resistance, physiological responses, and miRNA expression profiles were systematically analyzed. Compared with C/C, the disease index of C/R was reduced by 63.17%, whereas C/S showed only a modest reduction (9.65%), indicating pronounced rootstock-dependent differences in scion resistance. Consistently, C/R plants exhibited significantly enhanced activities of antioxidant enzymes (SOD, POD, and CAT) and key enzymes involved in phenylpropanoid metabolism, along with effective alleviation of membrane lipid peroxidation. In contrast, C/S plants displayed limited activation of defense-related enzymes and suffered from increased oxidative damage. At 48 h postinoculation, a total of 209 miRNAs were identified. Differentially expressed miRNAs were mainly distributed among C/R-specific miRNAs (28%), miRNAs shared among all graft combinations (14%), and miRNAs shared between C/R and C/S (3.5%). Target gene analysis revealed that these miRNAs predominantly regulate hormone-related transcription factors, signal transduction components, defense metabolism-related genes, and genes associated with membrane homeostasis. qRT-PCR further confirmed that the miR156c-5p – SPL13, miR169f-5p – BAK1 , and miR172a-3p – RAP2–7/SCD1 modules exhibited contrasting regulation between C/R and C/S. These results demonstrate that rootstock genotype shapes scion resistance through coordinated physiological and miRNA-mediated regulation, providing insights into graft-induced disease resistance and potential targets for molecular breeding.
Chen et al. (Fri,) studied this question.