Effect of seed treatment with putative defence priming chemicals on defence-related gene expression and pathogen resistance in Norway spruce (Picea abies) seedlings
Chemical seed treatment may be a simple method to protect conifer seedlings from pests and pathogens in plant nurseries and forest stands. In this study, I tested the ability of eight putative defence priming chemicals (methyl jasmonate (MeJA), β-amino butyric acid (BABA), hexanoic acid, gibberellic acid, quinic acid, thiamine, riboflavin and chitosan) to enhance the resistance of Norway spruce (Picea abies) seedlings by means of seed treatment. I carried out two different tests on young spruce seedlings grown from seeds soaked overnight in priming chemicals: I tested (1) 10-day-old seedlings for resistance to the oomycete Pythium ultimum, and (2) 10-week-old seedlings for expression of selected defence-related genes (ACS, LOX, PAL1, TPS-Car and Chi4) after mechanical wounding. In addition, I measured germination rates of treated seeds and root length of 8-day-old seedlings grown from treated seeds. None of the seed treatments I tested caused significant changes in seedling resistance to P. ultimum, gene expression, or the percentage of seeds that germinated. All seed treatments significantly accelerated seed germination, except from BABA (0.1 mM and 0.5 mM), quinic acid (0.1 mM) and riboflavin (0.5 mM). Seed treatment with MeJA (0.05 mM and 0.1 mM) led to a significant decrease in seedling root length, while treatment with BABA (0.5 mM) and gibberellic acid (0.1 mM and 0.5 mM) led to an increase in root length. Overall, I could not demonstrate that any of the tested seed treatments has the potential to enhance the resistance of young spruce plants. My results do illustrate the importance of evaluating fitness costs in studies on seed priming
