Data from: Environmental variables associated with Nothophaeocryptopus gaeumannii population structure and Swiss needle cast severity in Western Oregon and Washington

The environment has a strong influence on the abundance and distribution
of plant pathogenic organisms, and plays a major role in the causation of
plant disease. Climatological factors may also alter the dynamics of the
interactions between plant pathogens and their hosts. Nothophaeocryptopus
(=Phaeocryptopus) gaeumannii, the causal agent of Swiss needle cast (SNC)
of Douglas-fir, is endemic to western North America where it exists as two
sympatric, reproductively isolated lineages. The abundance of this fungus
and the severity of SNC are strongly influenced by climate. We used
statistical and population genetic analyses to examine relationships
between environment, pathogen population structure, and SNC severity.
Although N. gaeumannii Lineage 2 in western Oregon and Washington was most
abundant where SNC symptoms were most severe, we did not detect a
significant relationship between Lineage 2 and disease severity. Warmer
winter temperatures were inversely correlated with foliage retention (AFR)
and positively correlated with the relative abundance of Lineage 2 (PL2).
However when distance inland, which was strongly correlated with both AFR
and PL2, was included in the model, there was no significant relationship
between Lineage 2 and AFR. Spring/early summer dew point temperatures also
were positively associated with total N. gaeumannii abundance
(colonization index (CI)), and inversely correlated with AFR. Warmer
summer mean temperatures were associated with lower CI and higher AFR. Our
results suggest that the two lineages have overlapping environmental
optima, but slightly different tolerance ranges. Lineage 2 was absent from
more inland sites where winters are colder and summers are warm and dry,
while Lineage 1 occurred at most sites across an environmental gradient
suggesting broader environmental tolerance. These relationships suggest
that climate influences the abundance and distribution of this
ecologically important plant pathogen, and may have played a role in the
evolutionary divergence of these two cryptic fungal lineages.