[Comprehensive evaluation of drought resistance in seedlings of the Populus 'Shaxin' series (hybrid progeny of poplars) in the Three-North Region, China].

To breed new drought-resistant poplar varieties suitable for the Three-North Region, we used Populus alba var. pyramidalis (PaP) (with strong drought resistance but weak insect resistance) and P. deltoids 'Shalin-yang' (PdS) (with weak drought resistance but strong insect resistance) as hybrid parents. We cultivated their hybrid progenies P. 'Shaxin 2' (PdSPaP_2), P. 'Shaxin 3' (PdSPaP_3), and P. 'Shaxin 4-1' (PdSPaP_4) as research objects, with the parents as controls in the solar greenhouse (day temperature: 25-28 ℃, night temperature: 18-20 ℃, relative humidity: 60%-70%, photosynthetically active radiation: 800-1000 μmol·m-2·s-1). After a 21-day artificial drought stress, the changes in anatomical structure, physiological and biochemical characteristics, and photosynthetic parameters of each variety at the seedling stage were compared. The results showed that the epidermal thickness of young stems of PdSPaP_4 was not significantly different from that of PaP, but significantly higher than that of other varieties. After 21 days of drought, PdSPaP_2 died due to rapid water loss and severe damage in the membrane system, while the other varieties, though showing wilting, remained alive. Leaf relative water content (RWC) of PaP decreased from 89.4% to 50.4%, and that of PdSPaP_4 decreased from 91.6% to 42.5%. The two varieties had the lowest increase rates in relative electrical conductivity (REC), indicating the least membrane damage. PaP and PdSPaP_4 initiated stomatal closure on the 7th day of drought, and the decrease rate of their photosynthetic rate on the 21st day was significantly lower than that of PdS. In conclusion, drought resistance of the P. 'Shaxin' series was ranked as: PdSPaP_4 > PdSPaP_3 > PdSPaP_2. PdSPaP_4 had drought resistance close to that of its male parent (PaP) and thus has the potential to be used as the main poplar variety for shelterbelt construction in the arid areas of the Three-North Region.