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.