Molecular Mechanism of IBA-Induced Adventitious Root Formation in Peach Rootstock Cuttings

Problems such as difficult rooting are common in the cutting propagation of peach rootstocks. The objective of this study is to explore the formation of adventitious roots (AR) of peach rootstocks induced by exogenous 3-indole butyric acid (IBA), and to clarify the multi-dimensional regulation mechanism of IBA promoting root formation from the perspective of physiological and molecular integration, so as to provide theoretical support and technical reference for efficient asexual breeding of peach rootstocks.

Hardwood cuttings from the peach rootstock ‘GF677’ (a clonal line resistant to replanting) were used as experimental material. Water (CK) served as the control. Cuttings were immersed in IBA solutions at the concentrations of 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 mg·L^-1 at the base before being propagated by cuttings. The physiological and biochemical changes during rooting, along with related gene expression characteristics, were analyzed.

300 mg·L^-1 IBA was the optimal rooting concentration, achieving a rooting rate of 91%. The indole acetic acid (IAA), cytokinin (CTK) contents and IAA/CTK in ‘GF677’ CT (treated with 300 mg·L^-1 IBA) reached the peak at 21 d of rooting stage, and the IAA and CTK contents in ‘GF677’ CK (cuttings with the base soaked in water) were lower than those in ‘GF677’ CT during the whole test period. The total nitrogen (TN) content of ‘GF677’ CT reached the peak at 28 d, and total phosphorus (TP) and total potassium (TK) contents reached the peak at 21-28 d. The peroxidase (POD) activity was highest at 7 d, while the indoleacetic oxidase (IAAO) activity decreased first and then increased at the cutting stage. The soluble sugar content of the two treatments showed a downward trend, and the ‘GF677’ CT was higher than the ‘GF677’ CK after 21 d. During the cutting period, the MDA content in the ‘GF677’ CK group was consistently higher than that in the ‘GF677’ CT group, with two peaks observed (at 7 and 21 d). In the ‘GF677’ CT group, MDA content peaked at 35 d (74.07 g·kg^-1). Transcriptome analysis revealed that IBA treatment significantly enriched pathways including plant hormone signaling, nitrogen metabolism, and sugar metabolism. In the hormone pathways, auxin-responsive genes such as Aux/IAA and AUX1, along with cytokinin response factors like B-ARR, exhibited differential expression; key genes in the abscisic acid (ABA) signaling pathway (e.g., PYR/PYL) were significantly downregulated. In the nitrogen metabolism pathway, nitrogen transporter genes (Nrt) were significantly up-regulated, while nitrate reductase genes (NR) were down-regulated. In the sugar metabolism pathway, hexokinase genes (HK3) showed enhanced expression, while sucrose phosphate synthase genes (SPS1) and starch synthesis-related genes (SS1, GBSS, SBE1) were significantly down-regulated, indicating a shift in carbon metabolism from sucrose and starch synthesis toward breakdown for energy supply.

300 mg·L^-1 IBA promotes adventitious root formation in ‘GF677’ by synergistically regulating endogenous hormone homeostasis, driving the redistribution of mineral nutrients and carbon sources toward the basal region of cuttings, and integrating multi-level molecular pathways including hormone signaling, nitrogen assimilation, and glycolysis/catabolism.