Phenotypic characterization of leaf tissue showed higher percentage of salinity tolerant plants in UCB1 compared to P. integerrima
Pistachia integerrima (also known as PGI) and the hybrid UCB1 (P. atlantica x P. integerrima ) are popular commercial rootstocks with P. vera scion cultivars (Zohary and Spiegl-Roy, 1975; Holtz et al., 2005). Earlier studies demonstrated the superior salinity tolerance of UCB1 rootstock compared to its paternal genotypeP. integerrima (Ferguson et al., 2002). In order to better understand the origin of their different salt tolerances, we assessed the variation within and between UCB1 and P. integerrimaseedlings. Individual plants were treated with 100 mM NaCl for 7 days and compared to 0 mM control plants of identical age (Fig. 1a). Salt tolerance was qualitatively assessed by the severity of leaf senescence or burn symptoms. Plant phenotypic classification after salt treatment was divided into three categories: 1) “high tolerance” when their leaf phenotype was indistinguishable from those of untreated plants, 2) “low tolerance” when over 75% of their leaves showed burns and / or senescence, 3) “moderate tolerance” when plants had an intermediate phenotype between that of “high tolerance” and “low tolerance”. Based on this phenotypic characterization, over 40% of UCB1 plants demonstrated high tolerance for salinity, which is approximately twice the rate observed for P. integerrima (Fig. 1b). The dioecious nature of wind pollinated pistachio results in a heterogeneity of the seedlings (Ahmad et al., 2005), which likely contributed to the observed variation. Together, these data demonstrated that the UCB1 genotype has a higher percentage of plants with leaf traits indicative of high salinity tolerance, corroborating previous studies (Ferguson et al., 2002). The observed differences between UCB1 and P. integerrimawere further explored to dissect their respective mechanisms of salinity tolerance.