Plant material and growing conditions
P. integerrima and UCB1 seeds were provided by Foundation Plant Services, University of California (Davis, CA, USA), the Kresha Agricultural Nursery (Bakersfield, CA, USA) and from the Wolfskill Experimental Orchard (Winters, CA, USA).
Pistachio seeds were separated from shells and sterilized in a mixture of 5% (V/V) bleach and 1% (V/V) Tween-20 in deionized water. Seeds were germinated in vitro in ½ Murashige-Skoog (MS) medium at adjusted pH of 5.7 containing 1% (W/V) sucrose, 0.1% (W/V) activated charcoal, and 0.75% (w/v) agarose. The media were supplemented with 4.5 µM 6-Benzylaminopurine, 0.5 µM indole-3-butyric acid, 0.29 µM gibberellic acid. Germinated seedlings were grown for 8 weeks for UCB1 and 10 weeks for P. integerrima in the same medium, at 22 ± 2°C using fluorescent light (100 to 150 mmol quanta PAR m–2 s–1) under long day conditions (16 h : 8 h light : dark). Plants were transferred to charcoal-free supplemented ½ MS medium for a minimum of one week prior to the start of the experiment.