Factors influencing the enlargement of trunk cankers of Phytophthora cinnamomi in red oak

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Development of cankers on red oak (Quercus rubra L.) caused by Phytophthora cinnamomi Rands was studied with dendrochronological techniques. Factors of variation among lesions were investigated. Lesion parameters proved to vary with the particular tree to which the lesion belonged. A discriminant factorial analysis and principal component analysis showed that this tree susceptibility was made up of two components. The first accounted for root infection and wound healing. The second concerned susceptibility to vertical spread of the pathogen in bark tissues. Relationships between (i) tree susceptibility and (ii) tree age and vigor were studied. From the occurrence of the first lesion at the collar, number and severity of lesions increased with time, following an exponential and logistic curve, respectively. A comparison of ring widths in infected and healthy trees showed that the disease had no detrimental effect on tree growth. However, annual necrosis length was positively correlated with the annual radial tree growth. The observed differences among trees could not be explained by the effects of time and vigor only. Temperature and drought were analyzed to determine their effect on lesion development. No direct effect of drought on this disease could be shown. The low cold hardiness of P. cinnamomi in the trunk was determined.

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