Seasonality and chemical elicitation of defense oleoresin production in field-grown slash pine under subtropical climate

Abstract

Oleoresin is a key defense strategy of advanced gymnosperms, based on the combination of a complex anatomical structure of resin ducts and elaborate terpene biochemistry. Given the vast array of oleoresin economic applications in the chemical, pharmaceutical, agrochemical, and biofuel industries, translating factors that regulate terpene biosynthesis into higher oleoresin yield is a challenge for the forestry industry. Field tests with approximately 3,500 28-year-old slash pine (Pinus elliottii Engelm. var. elliottii) trees were carried out from 2005 to 2008, under the subtropical climate of Southern Brazil, in order to examine the seasonal profile of oleoresin production stimulation in response to different chemical adjuvants, after mechanical injury. Yields of trees treated with oleoresin-inducing pastes containing alternative adjuvants were compared to the standard commercial one used on an industrial scale (based on the ethylene-releasing compound-2-chloroethylphosphonic acid-CEPA). Significant increases in pine oleoresin yield were observed by modulating its biosynthesis and using chemical stimulants affecting defense responses (benzoic acid, used in addition to CEPA) and biosynthetic enzymes (metal cofactors of terpene synthases, iron or potassium, used as replacements for CEPA). Oleoresin stimulation was consistent over at least four consecutive years. Overall effectiveness of oleoresin yield adjuvant stimulation was higher in the faster growth seasons, although potassium was effective in all of them. Combining metal cofactors did not show synergistic or additive interactions. The results suggest that higher oleoresin yields can be obtained by using individual adjuvants of the same signaling pathway in a season-specific fashion.