Purpose: This investigation was aimed to improve the salt tolerance of medicinal pumpkin by seed priming with putrescine and to explore the possible physiological basis of salinity tolerance. Methods: The factorial experiment based on a completely randomized design was performed to investigate the effect of putrescine pretreatment on seed germination percentage, mean germination times, seedling vigor index, seedlings radicle and plumule fresh and dry weights, seedling tissue water content, dry matter, photosynthetic pigments (chlorophyll a, b, total chlorophyll, and carotenoids), proline content, malondialdehyde, and α-amylase enzyme activity of medicinal pumpkin under salinity stress. The treatments consisted of three levels of seed priming with putrescine (0, 0.5, and 1 mM) and four salinity levels (0, 30, 60, and 90 mM of NaCl). Results: With increasing salinity, germination percentage, seedling vigor index, radicle and plumule fresh and dry weights, and their ratio, tissue water content, dry matter, photosynthetic pigments, and α-amylase activity were reduced. However, in the seeds which had been pre-treated with putrescine, these traits were higher than untreated seeds. Moreover, under salinity stress, mean germination time, proline, and malondialdehyde contents were increased and priming with putrescine reduced them. Also, seedling vigor index had a negative correlation with proline, malondialdehyde, and mean germination time, but there was a positive correlation between seedling vigor index and germination percentage. In addition, proline was significantly correlated negatively with germination percentage, radicle and plumule fresh weights, and plumule dry weight. Conclusions: Seed priming with putrescine (especially at 1 mM concentration) can improve the germination characteristics and seedling growth of the medicinal pumpkin under salinity stress.

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