Dissertation Defence: The Effect of Abiotic and Biotic Plant Stress on Phaeomoniella chlamdospora Abundance and Disease Development in Young Grapevines
June 10 at 1:00 pm - 5:00 pm
Jared Hrycan, supervised by Dr. Miranda Hart, will defend their dissertation titled “The Effect of Abiotic and Biotic Plant Stress on Phaeomoniella chlamdospora Abundance and Disease Development in Young Grapevines” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biology.
An abstract for Jared Hrycan’s dissertation is included below.
Examinations are open to all members of the campus community as well as the general public. Registration is not required for in person exams.
ABSTRACT
Young vine decline (YVD) fungal pathogens cause internal necrosis, leading to stunted growth and eventual plant mortality within the first few years after planting. Canada’s fast-growing grape and wine industry depends on the import of nursery propagated material but the health status of ready-to-plant nursery grapevines in Canada regarding YVD fungi is unclear. A nursery survey was conducted to investigate the presence or absence and quantity of the most prevalent YVD pathogens reported in other countries. 99% of plants contained at least one YVD pathogen, and overall, a mean of 3 YVD fungal species were found in each grapevine. Pathogen abundance for each fungus in single plants was conducted using droplet digital PCR. Results showed fungal abundance to vary widely between nurseries, grapevines, and different parts of the same grapevines. Additionally, several YVD pathogens were isolated that had not previously been reported in Canada, showing that nursery material can be the source or new fungal pathogens in Canadian vineyards.
Phaeomoniella chlamydospora (Pc), one of the main agents of the YVD Petri disease, was found in up to 80% of ready-to-plant nursery grapevines. The presence of Pc in asymptomatic nursery grapevines has led to the hypothesis that it may be a latent pathogen, transitioning from an endophyte to a pathogen under plant stress. Two greenhouse and four field experiments were conducted to determine the effect of drought stress, heat stress, j-rooting, and ring nematode infestation on Pc abundance and disease development in young grapevines. Arbuscular mycorrhizal (AM) fungi were inoculated in the greenhouse to investigate whether a reduction in plant stress due to AM fungal colonization would reduce Pc abundance. In the greenhouse, a combination of drought stress and AM fungal colonization increased Pc abundance. In the field, while not statistically significant, plants inoculated with 2,500 Pc conidia and exposed to drought stress, j-rooting, and heat stress had higher symptoms’ development and mortality than 2,500 non-stressed plants. Additionally, while not statistically significant, plants initially inoculated with 25,000 spores had higher symptoms’ development and mortality regardless of stress. Ring nematode infestation had no impact on Pc abundance or disease development in the greenhouse or field. These findings suggest a relationship between plant stress, Pc abundance, and subsequent disease development in young grapevines within a few years after planting.
