The effect of rootstock on the anatomy of the Phaseolus vulgaris L. scion: graft union, stomatal density, stomatal index, and leaf thickness

Objective: To evaluate the effect of the Phaseolus acutifolius A. Gray rootstock on the establishment of the Phaseolus vulgaris L. scion, analyzing the anatomy of the graft union, stomatal density, stomatal index, and leaf thickness. Design/Methodology/Approach: A completely randomized experimental design was used. The experimental unit consisted of one plant per pot. Data were analyzed using Tukey's Mean Comparison Test (p ≤ 0.05). Some segments of the graft union were fixed in formaldehyde-acetic acid-alcohol (FAA), embedded in paraffin, and stained with safranin and fast green, while others were analyzed fresh. Fragments of the central leaflet, fixed in 3% glutaraldehyde and processed for observation under a Scanning Electron Microscope, were used to describe leaf anatomy. Results: Five stages were identified during the formation of the graft union: development of the necrotic layer, callus proliferation, vascular cambium differentiation, vascular tissue restoration, and restoration of the epidermis. Grafted plants recorded increases of 20%, 24.7%, and 66% in stomatal density, stomatal index (on the underside of leaves), and in mesophyll thickness, respectively. Study Limitations/Implications: The Phaseolus acutifolius rootstock was used in the anatomical evaluation of the Phaseolus vulgaris scion under irrigation. Findings/Conclusions: The anatomical compatibility between rootstock and scion was confirmed, allowing the development of new plants with foliar micromorphological characteristics that modify their physiological behavior.