Botryosphaeria ribis Infection Associated with Death of Eucalyptus radiata in Species Selection Trials

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Abstract
Dark brown discoloration of the phloem and light purplish brown discoloration of the xylem were associated with death of Eucalyptus radiata in species selection trials. Xylem discoloration and extensive kino veins often formed ahead of phloem necrosis. Of the 22 trees examined, Botryosphaeria ribis was isolated from lesion margins in 13 trees and Cytospora eucalypticola, from lesion margins in 12 trees. In glasshouse and field pathogenicity tests, E. radiata was the only Eucalyptus species of the four tested where there was both considerable longitudinal and tangential extension of B. ribis in the phloem. The fungus was confined in E. calophylla and E. cladocalyx, and callus formed at the lesion margins. B. ribis became established in the phloem of E. marginata but was contained by the formation of necrophylactic periderms. C. eucalypticola failed to establish in E. cladocalyx and was contained in E. marginata abd E. radiata phloem. The environment of trial sites in the low-rainfall zone of the E. marginata forest may be marginal for E. radiata, and environmental stress may have been a predisposing factor affecting resistance to infection.