Pathological anatomy of needles of Pinus strobus exposed to carbon-filtered air or to three times ambient ozone concentrations, or infected by Canavirgella banfieldii

A necrosis of succulent, elongating, current-year needles of Pinus strobus in the northeastern United States, frequently attributed to 'ozone damage,' is not due to ozone. The pathological anatomy of affected needles differs from that described for ozone injury and is virtually identical to that described as 'semimature-tissue needle blight.' The syndrome on affected trees throughout the northeastern United States is consistently associated with the presence of the needlecast fungus, Canavirgella banfieldii. This fungus occurs in the mesophyll of both healthy appearing and dying tissues of such needles before these needles have elongated to half their mature size. The pathological anatomy of infected needles agrees with that described for needlecasts by other researchers, beginning with R. Hartig. In contrast, healthy clones of field-symptomatic and field-asymptomatic trees exposed in open-top chambers to carbon-filtered air and to air adjusted on an hourly basis to 3× ambient ozone concentrations incurred a distinctly different tip necrosis. These necrotic tissues were delimited by an intercellular gummy deposit of unknown composition that appeared to be a type of walling-out response. No hyphae were present in these needles. The pathological anatomy of such needles resembled neither that of the symptomatic parent trees in the field, nor that previously demonstrated in various conifers as due to ozone.