Preliminary Selection of Some Pear Rootstocks for Tolerance to Deficit Irrigation Stress Based on the Growth and Physiological Indices

Tolerance to drought stress is important characteristic related to growth of pear trees and selection of rootstocks for orchard establishment. In this research, growth and physiological indices were evaluated in several pear rootstocks including; micropropagated Dargazi, Pyrus betulifolia and three clonal rootstocks; Pyrodwarf, OH×F69 and OH×F87 after 60 days in deficit irrigation conditions. Deficit irrigation levels were 75% and 50% of filed capacity and non- stress condition as control were implementend in greenhouse. P. betulifolia and OH×F87 rootstocks demonstrated the highest and lowest growth rate and tolerance to the deficit irrigation conditions based on relative growth rate (RGR) and leaf number (tgαln). Monthly evaluation of leaf relative water content (RWC), proline, total carbohydrates and total proteins as well as membrane stability and electrolyte leakage showed that P. betulifolia with 72.1% RWC had the lowest level of this index in optimal (control) condition. However, despite the highest reduction of RWC to 57.1 and 58.3, on 30 and 60 days after deficit irrigation, respectively, in P. betulifolia, this rootstock could maintain the highest growth rate. Based on the results of this research the highest levels of tolerance to the deficit irrigation was observed in P. betulifolia followed by Pyrodwarf, OH×F69, Dargazi and finally OH×F87 rootstocks, respectively. These results showed the importance of selection of tolerant pear rootstocks and need for further orchard evaluation of them for establishment of pear orchards in stressful conditions.