Effect of tree age on Diplodia pinea infection of Pinus radiata.
Shoot dieback in P. radiata, caused by D. pinea infection, decreases in severity after trees reach 7-8 yr. When cuttings from ortets aged 3, 6, 9 and 15 yr were inoculated with D. pinea under 2 different conditions giving a high and a medium level of infection, however, all age classes proved equally susceptible. The reduction in infections is apparently not due to a stable change occurring in the apical meristem. A nutritional effect due to increased tree size and complexity, or simple disease escape due to changing environment in relation to tree height is a more likely explanation.<new para>ADDITIONAL ABSTRACT:<new para>Shoot dieback of P. radiata caused by D. pinea decreases in severity after trees reach 7-8 years old [cf. FA 38, 1445]. When cuttings from ortets aged 3, 6, 9 and 15 years were inoculated with D. pinea under two different conditions giving high or medium rates of infection, all age-classes were equally susceptible. There is little prospect of using cuttings from older trees to control dieback. Reasons for reduction in dieback in plantations are discussed.