Graduate Thesis Or Dissertation
 

Studies on canker in European filbert caused by Anisogramma anomala

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  • Anisogramma anomala causes a stem canker of filberts, Corylus avellana. This disease became a threat to the main U.S. filbert growing region when it was introduced into the Pacific Northwest around 1968. Various methods of artificially inoculating filbert trees and seeds were explored. Less than 1% of potted filbert trees inoculated with ascospores produced symptoms after 4 years. The disease was not transmitted following graft inoculation of orchard trees with infected tissue. Ascospores had no effect on germination or growth of Corylus seedlings. Spread of existing cankers was compared on the susceptible cultivar 'Daviana' and the more resistant cultivar 'Barcelona'. There was no significant difference (t=.05) in canker elongation between cultivars, or between spread up and down the stems. Vertical elongation of perennial cankers averaged 26.2 cm/year. Methods for storing ascospores prior to germination, and conditions for germinating ascospores were explored. Spores exhibited no loss of viability after 2 months when cankered twigs were stored below 0° C. Ascospores remained viable for less than 14 days following discharge in water. Drying was lethal to hydrated spores. Ascospores commenced germination 24 hours after hydration when placed on a suitable medium in a proper atmosphere. Germination occurred between 5° and 25° C, with an optimum of 20°. Optimum pH for germination was between 4.2 and 5.7. A direct relationship was detected between ascospore concentration and percent germination. Eight antibiotics were screened in an attempt to prevent bacterial contamination. 10 ppm Rifampicin or 100 ppm Kanamycin effectively inhibited bacterial contaminants without affecting ascospore germination. Germination was compared on many different complex and defined media, and with different amendments added to the media. Various Corylus extracts had no effect on spore germination. 1% ethanol and 5% sucrose increased germination. Casamino acids, cornmeal or peptone promoted growth beyond the initial germ tube. Several stages of ascospore germination and early hyphal growth are described.
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