Anatomical traits in pine stems, the first step to define grafting combinations?

Grafting in pine species began in the 1960s; however, no current studies provide anatomical descriptions of scions and rootstocks before grafting. Consequently, this research analyzed the initial anatomy of scions of Pinus greggii var. australis Donahue & López produced in nurseries and on-field and rootstocks from four pine species. Stem fractions of rootstock ( P. greggii var. australis , P. patula Schiede ex Schltdl. et Cham., P. teocote Schiede ex Schltdl. et Cham., and P. leiophylla Schiede ex Schltdl. et Cham.) and scions of P. greggii var. australis were fixed and processed by paraffin-embedding microtechnique. The width of pith, xylem, vascular cambium + phloem (VC-P), cortex, and epidermis + peridermis (E-P) were measured. For tracheids, the variables measured were tangential and radial diameter, area, and relative hydraulic conductivity (RHC). Mixed models identified differences among species with the GLIMMIX procedure. Results showed that rootstocks from P. patula and P. leiophylla had higher values of VC-P, while P. teocote had the smallest tracheid area. The field-grown scions showed greater VC-P and cortex width. In contrast, tracheids from nursery scions had the largest diameters and areas. Based on the similarity of the anatomical traits measured, the most successful grafting combinations are nursery scion / P. leiophylla and field-grown scion / P. patula. Our study highlights the importance of anatomical characterization before grafting.