Aspen Bibliography

Colletotrichum shoot blight of Poplars

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Forest Science





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In Wisconsin, two different fungi caused shoot blight and defoliation of Populus tremuloides and of P. alba Xtremuloides trees. The pathogenicity of Pollaccia radiosa, established previously elsewhere, was corroborated. In the field, Colletotrichum gloeosporioides was recovered initially from a P. alba X tremuloides hybrid and later from P. tremuloides. The morphology of this pathogen is described and its taxonomy is discussed. In the greenhouse it caused leaf lesions on P. alba, P. tremula and P. alba X tremuloides trees. On P. tremuloides it caused leaf, petiolar, and stem lesions; vein necroses; and shoot dieback. Shoot blights caused by P. radiosa and by C. gloeosporioides were distinguished easily by leaf symptoms. Colletotrichum gloeosporioides sporulating cultures survived at -15°C for 4 months. On dry leaf surfaces at 28°C conidia remained viable for 4 to 8 days. The optimum temperature for growth and sporulation of the pathogen and for infection and disease development was 24°C. Incubation of inoculated trees in mist chambers for 6 to 48 hours, depending on the temperature, was necessary for infection. After the germination process started, neither conidia nor appressoria were resistant to desiccation. The fungus remained vulnerable to dry conditions until leaves were penetrated. The pathogen is a relatively cool weather anthracnose fungus, apparently depending primarily upon meteoric water for its dissemination.