Creation of new varieties of tetraploid willow (Salix suchowensis) and their evaluation for salt tolerance.

To break the germplasm bottleneck that constrains afforestation in coastal and inland saline alkali soils, this study focused on Salix spp., a fast growing, ecological tree genus, and aimed to establish a highly efficient, low chimera protocol for tetraploid willow induction through refined colchicine treatment. The overarching objective was to expand forest genetic diversity and provide both theoretical insights and elite plant materials for the development of salt-tolerant willow cultivars. The colchicine-based chromosome doubling procedure was systematically optimized; 0.1% (w/v) colchicine for 12 h was identified as the optimal condition, and ploidy levels were verified by flow cytometry. Compared with the diploid controls, the induced tetraploids exhibited pronounced gigas characteristics: leaf length and width increased by 1.6- and 1.4-fold, respectively, and leaf fresh weight was 2.4-fold higher. After 14 d of 50 mmol/L NaCl treatment, tetraploids contained only 50% of the K⁺ level observed in diploids, resulting in a significantly higher K⁺/Na⁺ ratio. POD activity in tetraploids was approximately twice that of diploids, and total chlorophyll content was likewise 1.2-fold higher, collectively demonstrating superior growth performance and physiological homeostasis under saline conditions. These results demonstrate that the optimized chromosome doubling protocol markedly improves tetraploid induction efficiency and effectively enhances the salt tolerance of S. suchowensis. Future research will integrate whole genome re-sequencing to dissect dosage effects and identify key genomic loci governing salt tolerance, establish a marker assisted selection framework for accelerated tetraploid breeding, and conduct multi-site field trials to comprehensively evaluate stability and ecological adaptability. Such efforts are expected to expedite the commercial deployment of high salt tolerant willow cultivars in coastal shelter belt construction and large-scale saline alkali land restoration.