Formation of traumatic resin ducts in the phloem of western redcedar (Thuja plicata) roots following abiotic injury and pathogenic invasion by Armillaria ostoyae

Anatomical changes involved in traumatic phloem resin duct (TPRD) formation in western redcedar (Thuja plicata) roots were examined following abiotic wounding and fungal invasion by Armillaria ostoyae. Following necrophylactic periderm formation, hyperplasia and expansion of a band of phloem parenchyma cells occurred in close proximity to the vascular cambium and schizogenous and lysigenous separation of its derivatives resulted in a series of longitudinal resin ducts in the inner to mid-phloem region. Fungal invasion appeared to amplify traumatic resin duct formation in the phloem. While traumatic cavities in the phloem have been reported for other Cupressaceae, this is the first report documenting TPRD formation in western redcedar.