Date of Award

8-2012

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Seanna Annis

Second Committee Member

David Lambert

Third Committee Member

Paul Rawson

Abstract

Mummy berry disease, caused by the fungal pathogen Monilinia vaccinii-corymbosi, is a major problem affecting lowbush blueberry (Vaccinium angustifolium) production. Damage caused by mummy berry disease results in major economic losses for lowbush blueberry growers. In Maine and Canada, mummy berry disease is typically managed through 1 to 3 treatments of site-specific demethylation inhibiting (DMI) fungicides applied to lowbush blueberry each crop year in a two-year crop cycle. This practice of using biennial, repeated applications of a single fungicide to control mummy berry disease may increase the risk of M. vaccinii-corymbosi developing fungicide resistance. A preliminary study tested the sensitivity of 82 isolates of M. vaccinii-corymbosi to the DMI fungicides, propiconazole and fenbuconazole, at three concentrations, 0, 0.01 and 0.1 |ag/mL. Results from these initial trials were used to determine the range of concentrations to be tested to measure the EC5o (dose necessary to reduce mycelium growth by 50%) of propiconazole and fenbuconazole for M. vaccinii-corymbosi. The sensitivity of 79 isolates of M. vaccinii-corymbosi from 3 types of fields: 4 conventionally managed, 3 organically managed and 1 unmanaged, was determined for propiconazole and fenbuconazole using six fungicide concentrations, 0, 0.01, 0.03, 0.07, 0.1 and 0.3 |ag/mL. A baseline EC50 for each fungicide was established using the fungicide sensitivity data of isolates from the unmanaged area. The baseline EC50 was significantly higher for propiconazole (0.016 (ig/mL) than fenbuconazole (0.00059 |ig/mL). No significant (p> 0.05) differences in the fenbuconazole EC50 were found among management types. The propiconazole EC50 for conventionally managed fields (0.020 (ig/mL) was significantly higher than for the unmanaged area (0.016 (ag/mL). The propiconazole EC50 for organically managed fields (0.018 (ig/mL) was not significantly different from those of the other field types. The continual, biennial use of the fungicide propiconazole on populations of M. vaccinii-corymbosi may act as a selection pressure within conventionally managed fields and cause the development of fungicide insensitivity over time. Understanding the effects of fungicide use as a selection pressure on populations of M. vaccinii-corymbosi may aid in the development of more effective treatment methods to reduce future fungicide resistance in the field. We attempted to determine the population structure of M. vaccinii-corymbosi in these same fields using 40 microsatellite primer sets developed for 5 different fungal species in the family Sclerotiniaceae. Of the 40 primer sets tested, 29 amplified DNA from M. vaccinii- corymbosi', however, none of the microsatellite primers tested appeared to amplify microsatellite loci. Decreased sensitivity to propiconazole may be occurring in M. vaccinii-corymbosi in Maine’s conventionally managed lowbush blueberry fields; however, no fungicide resistance has yet been seen in blueberry fields. In the future, using microsatellite markers specific for M. vaccinii-corymbosi may allow us to gain insight into how fungicide use may be acting as a selection pressure in lowbush blueberry fields, but this will require the development of species-specific primer sets.

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