Morphological and molecular characterization of interspecific hybrid pistachio rootstocks

Interspecific hybrid pistachio rootstocks derived from wild Pistacia species offer promising combinations of vigor and stress tolerance but require detailed morphological and molecular characterization before registration and deployment. This study evaluated 13 genotypes—four hybrid rootstocks (‘Arota 1’, ‘Arota 2’, ‘Arosha’, ‘UCB1’), five parental accessions, and four commercial P. vera cultivars—using 12 standardized UPOV leaf descriptors and five SSR markers. Morphological analyses revealed three distinct clusters: wild species/hybrids (Cluster I), intermediate forms (Cluster II), and commercial cultivars (Cluster III). The hybrids retained several characteristic wild-type leaf features (smaller, more numerous, and more asymmetric leaflets) while remaining morphologically intermediate between their parental species. ‘Arota 1’ showed the greatest reduction in terminal leaflet length (TLL = 43.7 mm), whereas ‘Arota 2’ exhibited the highest terminal leaflet length-to-width ratio (TLLW = 3.89). MDS revealed coordinated trait variation (MDS1: 50.1% variance). SSR analysis (mean PIC = 0.60) separated the wild/hybrid and cultivated P. vera germplasm via PCoA. SSR analysis identified candidate diagnostic alleles for P. atlantica (Ptms9_163) and P. integerrima (Ptms10_158 and Ptms41_236) that supported parentage verification within the evaluated germplasm. Exclusion analysis further validated the reported parentage of ‘Arosha’ ( P. integerrima × P. vera ). Together, the standardized UPOV descriptors and SSR markers provide a practical framework for DUS testing, nursery certification, pedigree verification, and clonal propagation of interspecific pistachio rootstocks.