Characterization of Fusarium graminearum from Acacia and Eucalyptus using β-tubulin and histone gene sequences

Abstract During routine surveys of diseased Acacia mearnsii and Eucalyptus grandis in South Africa, isolates of an unknown, nonsporulating fungus with a red mycelium were collected. Symptoms associated with the disease included branch dieback and stem cankers on both hosts. None of the isolates of the fungus produced spores, making identification using morphological characteristics impossible. An attempt was thus made to identify the isolates using DNA sequence data for the β-tubulin and histone genes. Using this approach, the fungus was tentatively identified as Fusarium graminearum. Sequences were then compared to those for isolates of F. graminearum from cereal hosts. The relative pathogenicity of F. graminearum to A. mearnsii and an E. grandis clone was determined in pathogenicity trials. Pathogenicity tests were conducted by inoculating 18-mo-old A. mearnsii trees and 12-mo-old E. grandis clone trees under field conditions. All the isolates tested produced significant lesions on both the A. mearnsii and E. grandis clones. The isolates collected from A. mearnsii and E. grandis were further compared to other F. graminearum isolates using β-tubulin and histone gene sequence. In these comparisons the isolates collected from A. mearnsii and E. grandis consistently grouped with F. graminearum isolates. The occurrence of F. graminearum on A. mearnsii and E. grandis is intriguing, and as far as we are aware, this is the first report of the fungus associated with a disease of a woody host.

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