Gas Exchanges and Physiological Responses Differ Among ‘Pyrodwarf’ Clonal and ‘Dargazi’ Seedling Pear ( Pyrus communis L.) Rootstocks in Response to Drought Stress

Selecting appropriate scion-rootstock combinations, which are determined by the rootstock’s root system, is vital for successful orchard management. There are usually two types of rootstocks available for pear orchards, clonal as well as seedling rootstocks. This research aimed to examine how seedlings and clonal rootstocks respond and withstand soil moisture limitations and drought stress conditions. Two pear rootstocks including ‘Dargazi’ seedlings and ‘Pyrodwarf’ clones were used. The irrigation treatments were well-watered (100% FC), moderate (60% FC), and severe drought (30% FC). The physiological and gas exchange responses were measured at 30 and 60 days after stress treatment (DAT). Results indicated that stomatal restrictions were one of the main causes of photosynthetic limitations under drought stress in the studied pear rootstocks. Photosynthesis (A n ) in ‘Pyrodwarf’ was more affected by the leaf ABA concentration than in ‘Dargazi’ rootstock. In 60 DAT, ‘Dargazi’ seedlings improved gas exchange parameters, and root dry weight ( RDW ). The increase in proline and glycine betaine and decrease in leaf water content per unit leaf area ( LWCA ) under drought stress showed signs of osmotic adjustment in both studied rootstocks. Although at 30 DAT, the photosynthetic restriction of ‘Pyrodwarf’ was affected by the stomatal closure, in 60 DAT the limitation to photosynthesis is maybe non-stomatal. In conclusion, these findings showed that ‘Pyrodwarf’ adapts better to moderate and shorter duration of drought stress, and ‘Dargazi’ was more adapted to severe and long periods of drought stress. This is due to the direct interaction of the rootstock and scion in resistance to drought stress. Besides it can help to select suitable rootstock for orchards faced with moderate to severe drought conditions. Graphical Abstract