Effect of salt stress tolerance of four pear rootstock clones on the salt resistance of their grafted and the involvement of possible mechanisms

Abstract Soil salinity affects the distribution of fruit trees and limits the development of the fruit industry. Rootstock plays an important role in improving the stress resistance of fruit trees.This study investigates the effects of four pear rootstock clones —QNA201 ( Pyrus calleryana Decne.), QAUP-1 ( P. ussuriensis Maxim), QingzhenD1 ( P. communis L.× P. bretschneideri Rehd) and OHF40 ( P. communis L) on the salt tolerance of the grafted variety ‘Luxiu’( P.pyrifolia Nakai cv.’Luxiu’ ) and explores the underlying mechanisms. Rootstocks and grafted seedlings were subjected to different concentrations of NaCl treatments (0 mM, 100 mM, and 200 mM for rootstocks; 200 mM for grafted seedlings). A number of physiological and biochemical indexes were determined, including salt injury index, chlorophyll content, photosynthetic parameters ( P N , E T , gS ), activities of antioxidant enzymes (SOD, POD, CAT), as well as contents and distribution of Na⁺ and K⁺.The results showed that QNA201 and Qingzhen D1 exhibited strong salt tolerance, with lower salt injury indexes, more stable photosynthetic performance, and more favorable distribution of Na⁺ and K⁺. The aboveground parts of rootstocks QNA201 and Qingzhen D1 accumulated less Na⁺ and could maintain a higher K⁺ level. The salt tolerance of grafted seedlings was consistent with that of the rootstocks. L/QNA201 and L/Qingzhen D1 had less salt damage, higher SPAD values, and stronger antioxidant activity. Na⁺ was concentrated in the roots and grafting bases, while K⁺ was enriched in the aboveground parts (especially in the leaves of L/Qingzhen D1). Transcriptomic analysis revealed significant differences in gene expression related to hormone regulation, ion transport, and antioxidant pathways in salt-tolerant rootstocks. QingzhenD1 displayed higher expression of genes involved in salicylic acid synthesis, auxin and ethylene-responsive transcription factors, and the antioxidant system, indicating its role in enhancing salt tolerance. These findings highlight the potential of QNA201 and QingzhenD1 as effective rootstocks to improve the salt tolerance of pear cultivars.