Optimizing the relative water protection (RWP) as novel approach for monitoring drought tolerance in Iranian pistachio cultivars using graphical analysis

Abstract

Pistachio (Pistacia vera L.) is the most important agricultural crop in arid and semi-arid regions of Iran. In order to optimize and evaluate the ability of relative water protection (RWP) for screening drought-tolerant pistachio cultivars, twenty-one cultivars with wide range of tolerance to drought stress were collected from across the orchards of Rafsanjan (Iran’s center of pistachio cultivation) and were used in a randomized complete block design with three replications under two environmental conditions (normal and drought stress) in 2011-2012. Four different withering times (4h, 6h, 8h and 10h) for measuring RWP were compared to determine the best time for screening tolerant cultivars. The results showed that the RWP increased significantly (P < 0.05) under drought stress, but the increase was not significant in susceptible cultivars. The highest RWP was observed in tolerant cultivars and the lowest rate was detected in susceptible. The visualizing graphics of different statistical methods revealed that the diversity among the cultivars was increased when the withering time to measure RWP was longer (4h to 10h). Three groups of cultivars including tolerant, intermediate and susceptible were not clearly separated from each other at the times 4h and 6h. As a result, the measuring RWP at these withering times are not reliable to identify droughttolerant pistachio cultivars. The time 8h was suitable to separate drought tolerant cultivars from susceptible, but this time was not able to screen cultivars with high tolerance from intermediate under drought condition. The findings adopted the RWP measured at the withering time 10h as ideal time for classification and identification of drought tolerant cultivars. In the present study, Kale Ghoochi 1 and Ancient Badami were selected, respectively, as the most tolerant and susceptible pistachio