Defoliation increases nutritional quality and allelochemics of pine seedlings

The concentration of phenols, procyanidins, and protein in pine foliage was determined at two and eight weeks following mechanical defoliation of 0, 25, 50, and 75%. Changes in both mature and immature ponderosa pine, Pinus ponderosa Dougl. ex Laws, foliage were monitored. The lowest level of defoliation (25%) produced the largest increase in phenols; 75% defoliation caused the largest increase in procyanidins. The number of phenolic compounds in mature foliage doubled following 25% defoliation. Maximum protein production also occurred at moderate defaliation levels. Mechanical defoliation had a significant effect on the production of all compounds tested. The implications of these results for induced resistance research are discussed.