Upright dieback disease of cranberry, Vaccinium macrocarpon Ait.: Causal agents and infection courts.

摘要

The objective of this study was to determine the role of Phomopsis vaccinii in upright dieback disease of cranberry (Vaccinium macrocarpon). Specifically, the goals were to complete Koch's Postulates for P. vaccinii as a pathogen of cranberry, determine infection courts, evaluate the pathogenicity of various isolates of P. vaccinii and isolates of non-P. vaccinii Phomopsis from cranberry and blueberry (Vaccinium corymbosum), and determine which cranberry tissues P. vaccinii infects and colonizes.; Koch's Postulates were completed using tissue-cultured and rooted cuttings of two cultivars. It was therefore concluded that P. vaccinii is a causal agent of upright dieback disease.; Various infection courts were tested by conducting inoculations of different tissue using different wounding techniques. It was determined that, while non-wounded plants occasionally developed symptoms, stem-pierce wounds resulted in infection of more plants and typically greater tissue death than other wound techniques. A higher percent of plants on which current-year growth was inoculated developed symptoms compared to plants on which 1-yr-old growth was inoculated. It was concluded that current-year growth in spring was the most susceptible growth stage, although plants can be infected throughout the season if wounded. It was observed that only current-year growth was affected when infection occurred in the current-year growth, and infection did not progress to adjacent runners or uprights if the infection occurred in the 1-yr-old growth.; It was determined that isolates of P. vaccinii and non- P. vaccinii isolates of Phomopsis could result in symptom development on tissue-cultured cranberry plants and rooted cuttings of cranberry. More P. vaccinii isolates resulted in disease development than other Phomopsis sp. isolates. A few isolates did not result in symptom development on any inoculated plant, or resulted in symptom development on only a low percent of plants. Since these isolates were regularly isolated from symptomless tissue, it is probable that these isolates are non-parasitic endophytes of cranberry plants.; P. vaccinii-inoculated tissue-cultured plants were examined microscopically, and P. vaccinii was observed throughout necrotic leaf tissue and in vascular stem tissue. These observations indicate that P. vaccinii is a vascular pathogen. It is expected that the fungus infects succulent growth and progresses from leaf tissue into the stem tissue, or infects through stem wounds, eventually colonizing vascular tissue.