Early investigations into the infection courts used by Neonectria fuckeliana to enter Pinus radiata stems

Abstract

Nectria flute canker is a disease of Pinus radiata stems caused by the pathogen Neonectria fuckeliana occurring in the southern parts of New Zealand. In Northern Hemisphere countries where N. fuckeliana is endemic, it is commonly found in Picea and Abies spp. Open wounds, dead attached branches and branch stubs have been identified as the primary infection courts. Although in New Zealand the development of Nectria flute canker disease is associated with pruned branch stubs, recent studies suggest that this is not the only possible entry method as the fungus has been found in trees prior to pruning. Three field trials were established to examine the potential infection mechanisms for N. fuckeliana in P. radiata in New Zealand; including stem wounds and branch stubs. The difference between inoculations into the stem and into branch wood was clear. Inoculation of deep stem wounds resulted in the greatest fluting with 76% of trees inoculated developing cankers. Inoculation directly into stubs resulted in only small stem depressions that occurred in 17% of cases and the fungus was largely contained within the branch trace. Tree response to inoculation with either ascospores or conidia of the Acremonium anamorph gave similar results in terms of canker development and fungal spread within the stem. Tree response to inoculation was highly variable however: in one study 6% of trees did not respond to inoculation at all, while 26% produced severe cankers regardless of inoculation method. A more thorough understanding of the infection mechanisms of N. fuckeliana will contribute to the development of better disease management protocols to prevent infection and disease development in future plantation stock.