Effects of seed treatments on the physiological changes in soybean (Glycine max (L.) Merr.) induced by the presence of neighbouring weeds
In the absence of direct resource competition, the presence of aboveground neighbouring weeds can trigger shade avoidance responses in soybean seedlings through the detection of light quality changes by phytochromes. It was hypothesized that soybean seedling growing in the presence of aboveground weeds would not express typical shade avoidance morphology when soybean seeds were treated with thiamethoxam or calcium. Controlled environmental studies revealed that thiamethoxam-mediated increase in overall growth and nitrogen level could be attributed to the action of salicylic and jasmonic acids, while nodulation and isoflavonoid concentrations were modulated through a yet unknown pathway(s). Treatment of seeds with calcium prevented stem elongation and root growth inhibition in the presence of aboveground weeds when compared to untreated soybeans. Intriguingly, both calcium and thiamethoxam seed treatments prevented neighbouring weed-mediated induction of nitrate reductase activity. This study suggests that seed treatments can be used as a tool to enhance soybean’s competitive ability against neighbouring weeds.