Applications of Defense Elicitors to Roots of Containerized Eastern White Pine (<i>Pinus strobus</i>) Stimulate Increased Defensive Enzyme Activities of Fine Roots

Abstract The expansion of the use of induced resistance (IR) has been, and remains, an attractive prospect for the management of woody plants, but little research has occurred assessing the ability of elicitors to induce the root defenses of woody plants. Eastern white pine ( Pinus strobus ) was used as a model plant to assess IR elicitation. Containerized plants were treated with phosphite (Phi), chitosan, curdlan (a β-1,3-glucan polymer), or silicon (Si) on 2022 June 7. The soluble phenolic levels, tissue levels of major resin acids (abietic and neoabietic), as well as the activities of peroxidase (POX), chitinase (CHI), and β-1,3-glucanase (βGLU) of fine roots were compared across elicitor treatments and nontreated controls on June 10, June 14, and June 27. There were no changes post-treatment to soluble phenolics or resin acids at any sampling point, but chitosan treatment resulted in an increase in POX and CHI activities, while curdlan increased CHI activity on June 10. On June 14, curdlan-treated plants had significantly higher POX and CHI activities, while Phi-treated plants had significantly higher POX activity. By June 27, curdlan- and Phi-treated trees had significantly higher CHI activities. Our data suggest that chitosan, curdlan, and phosphite stimulate biochemical responses and potentially prime root systems to respond to subsequent stresses, but there appears to be variation between these elicitors regarding rapid versus longer lasting IR effects.