Effects of Photochemical Oxidant Injury of Ponderosa and Jeffrey Pines on Susceptibility of Sapwood and Freshly Cut Stumps toFomes annosus

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Abstract
Ponderosa (Pinus ponderosa Laws.) and Jeffrey (Pinus jeffreyi Grev. and Balf.) pine sapwood samples and freshly cut stumps from trees with different amounts of oxidant injury were inoculated with F. annosus. With stumps, percentage of surface cross-section area infected and extent of vertical colonization were determined 1 mo. and 6-10 mo. after inoculation, respectively. Increase in surface area infection with increased oxidant injury, expressed as upper-crown needle retention, was statistically significant for ponderosa pine (P = 0.01), but was not for Jeffrey pine. Also, the rate of vertical colonization was greater in stumps from severely oxidant-injured trees than in those from slightly injured trees. The relationship between injury and colonization was significant for Jeffrey pine (P = 0.05) and for ponderosa pine at one site (P = 0.03), but nonsignificant (P= 0.18) for ponderosa pine at a 2nd site. Increased susceptiblity of stumps to F. annosus appeared to be associated with decreased oleoresin exudation and decreased colonization by other fungi (especially Trichoderma spp. and blue stain fungi). Laboratory tests indicated that decay susceptibility of excised sapwood to F. annosus apparently was not affected by oxidant injury with Jeffrey pine, but weight loss of ponderosa pine sapwood was correlated with decreased injury (greater needle retention). Weight losses of Jeffrey pine caused by Polyporus versicolor and of ponderosa pine caused by Poria monticola were correlated with increased injury (increased needle chlorosis).