The Genetic Structure of Populations of the Douglas-Fir Swiss Needle Cast Fungus Nothophaeocryptopus gaeumannii in New Zealand.

Swiss needle cast is a foliar disease of Douglas-fir (Pseudotsuga menziesii) that results in premature foliage loss and reduced growth. The causal fungus, Nothophaeocryptopus gaeumannii, was first detected in New Zealand in 1959 and spread throughout the North and South Islands over the following decades. The contemporary genetic structure of the N. gaeumannii population in New Zealand was assessed by analyzing 468 multilocus SSR genotypes (MLGs) from 2,085 N. gaeumannii isolates collected from 32 sites in the North and South Islands. Overall diversity was lower than that reported from native N. gaeumannii populations in the northwestern United States, which was expected given that N. gaeumannii is introduced in New Zealand. Linkage disequilibrium was significantly higher than expected under random mating, suggesting that population structure is clonal. Populations of N. gaeumannii in the North and South Islands were weakly differentiated, and the isolates collected from sites within the islands were moderately differentiated. This suggests that gene flow has occurred between the N. gaeumannii populations in the North and South Islands, and between the local N. gaeumannii populations within each island. Eighteen isolates of N. gaeumannii Lineage 2, which has previously been reported only from western Oregon, were recovered from two sites in the North Island and four sites in the South Island. The most likely explanation for the contemporary distribution of N. gaeumannii in New Zealand is that it was introduced on infected live seedlings through the forestry or ornamental nursery trade, as the fungus is neither seed borne nor saprobic, and the observed population structure is not consistent with a stochastic intercontinental dispersal event.

Impact of Swiss needle-cast on growth of Douglas-fir.

Phaeocryptopus gaeumannii, the cause of Swiss needle-cast, is widely distributed in plantations of Douglas-fir in many parts of the world. Nevertheless, information remains limited on its precise effect on stand growth, particularly in relation to regional climate, and on its consequent economic cost. In New Zealand, the spread of P. gaeumannii over a period of ≈30 years following its discovery in 1959 was closely monitored, and the timing of its arrival in different forests is known. This information was coupled with data from permanent sample plots in order to quantify the associated historical growth increment loss. Analyses revealed a steady decline in growth rate over the period from the first appearance of P. gaeumannii to a point when it stabilized at a lower increment level 14 to 20 years later. The cumulative mean reduction was 25% for mean top height, 27% for basal area, and 32% for stem volume. Volume growth rate decline was greater in the North Island (35%) than the South Island (23%) of New Zealand. These reductions in volume growth are estimated to equate to a loss in net present value of $NZ2,620 ha(-1) and $NZ1,470 ha(-1) for the North and South Islands, respectively, using a discount rate of 6%. Mortality did not increase as a result of infection by P. gaeumannii. The disease had less effect on cooler sites, especially those with low spring minimum temperatures (P < 0.001). Negligible growth decline occurred on sites with daily minimum October temperatures averaging <3.2°C.

Stock-Type Susceptibility and Delineation of Treatment Areas for a Cryptic Pinus radiata Root Disease.

ABSTRACT Planting material with superior resistance to Armillaria root disease was identified in a field trial established to investigate variation in Armillaria infection among different Pinus radiata nursery stock types. At stand age 6.4 years, total infection incidence, mortality, and degree of root collar girdling by Armillaria spp. were all significantly lower among trees derived from both rooted stool bed cuttings (physiological age 1 to 3 years) and rooted field cuttings (physiological age 3 to 6 years) than among those grown from seedlings. Cutting types did not differ significantly from one another. No significant differences were found between stock types in stem diameter, but trees from stool bed cuttings were significantly taller than seedling trees. Whether these differences remain detectable later in the rotation, initial results suggest that it may be advantageous to plant robust stock, of either cuttings or seedlings, on Armillaria-infested sites. The incidence of infection in living, green-crowned trees was unevenly distributed across the trial site, and was greater nearer to trees killed by Armillaria spp. than further away (significant within a radius of 10 m). By mapping visible Armillaria-caused mortality prior to thinning, it may be possible to delineate areas with a higher incidence of concealed chronic infection, thus defining infested sites for postharvest treatment.