Lesion development in stems of rough- and smooth-barked Eucalyptus nitens following artificial inoculations with canker fungi

A study of lesion development in stems of Eucalyptus nitens following artif icial inoculations with canker fungi was carried out on 16-year-old plantat ion trees. In a first trial cambium bark wounds on smooth- and rough-barked trees were inoculated a with the mycelium of nine species of canker fungi, including Endothia gyrosa. In a second trial spores or mycelium of E. gyro sa were applied directly onto undamaged or superficially wounded bark surfa ces. Infection subsequent to artificial inoculation via wounding (whatever the wounding technique or type of inoculum) resulted in significantly large r compared with those on rough bark to 35.6 cm(2) 20 months after inoculati on) on smooth bark external lesions (mean lesion area (up to 19.0 cm(2)). M icroscopic studies of infected rough and smooth bark suggest that, once smo oth bark is compromised by wounding and artificial inoculation, the particu lar anatomical structure of smooth bark may offer less mechanical I resista nce to post penetration hyphal spread in comparison with rough bark. It is suggested that at a pre-penetration stage under natural conditions spores o f E. gyrosa mure easily infect rough hark via cracks associated with this t ype of bark but not present in smooth bark.