Growth environment and seedling age affect constitutive and inducible defence in radiata pine

There is increasing interest in induced resistance for crop protection. This study investigated effects of growth environment on inducible defences in developing radiata pine (Pinus radiata) seedlings. Seedlings were grown in the presence or absence of Trichoderma in either a temperature-controlled growth room or in a greenhouse. After 3, 5 or 7 months, seedlings were sprayed with 2.25 mm methyl jasmonate (MJ), 1 week before quantification of monoterpenes and total phenolics. The magnitude of induction of monoterpenes and total phenolics by MJ was inversely proportional to constitutive content, was greater in the greenhouse than the growth room and was greater at 3 months than at 7 months. This may indicate a cost-saving strategy to limit defence induction once constitutive defence reaches a certain threshold. Growth room seedlings expressed greater constitutive resistance to terminal crook (Colletotrichum acutatum) and to diplodia dieback (Diplodia sapinea) than greenhouse plants, consistent with the relative differences in constitutive defence chemistry. Indeed, while MJ induced resistance to diplodia dieback in both environments, there was no difference in terminal crook incidence (4.1%) between MJ-treated and untreated seedlings in the growth room. By the end of the study, growth room seedlings had c. 70% more β-pinene in stems and 140% more total phenolics in needles than greenhouse plants but were 40% smaller, indicating a defence–growth trade-off. Trichoderma did not have a significant effect on defence chemistry or on pathogen resistance. These results demonstrate the potential to manipulate defence in radiata pine by modification of the growth environment.