Responses to Inoculation With Diplodia Pinea in Progenies of Apparently Resistant Trees of Pinus Radiata

Abstract

A glasshouse inoculation trial with Diplodia pinea (Desm.) Kickx was carried out on 20 wind-pollinated progenies of Pinus radiata D. Don. The parents had been selected on a site of very high disease incidence for freedom from Diplodia-associated shoot dieback. Compared with two control seed lots the progenies as a whole showed less infection after an inoculation than the controls (69.7% v. 79.6%), this difference being statistically significant (P <0.05) in even the most stringent tests. The contrast was somewhat less marked in respect of shoot dieback (36.8% v. 44.4%). The progenies, however, were strongly variable among themselves, ranging from substantially less affected than the controls to marginally more affected. This suggests that there were some cases of real resistance with an additive genetic basis, although infection response seems to be only weakly heritable at the level of the individual.