Implications Of Production Practices On The Prevalence And Stability Of Fungicide Resistant Orchard Populations Of Venturia Inaequalis
Apple scab, caused by Venturia inaequalis, is one of the most economically important fungal diseases affecting apple production in temperate climates. Growers in these regions manage apple scab through the application of fungicide chemistries. The repeated usage of fungicide chemistries with a specific target site, such as Quinone outside Inhibitors (QoI) and demethylation inhibitors (DMIs), can have an impact on the orchard population structure in the number of resistant isolates that survive to reproduce. Many aspects regarding the development, prevalence, and stability of resistance to these fungicides is not completely understood for V. inaequalis. Two studies were carried out to determine how two different disease management practices affect the DMI sensitivity of V. inaequalis orchard populations. An additional study was performed to determine the prevalence and in vitro stability of QoI fungicide resistance in V. inaequalis. The first two studies provided data on the occurrence of DMI resistant isolates in V. inaequalis orchard populations either after a dormant chemical treatment or when difenoconazole (DMI fungicide) is applied throughout the production season as opposed to during the primary infection season only. The third study provided an understanding of the prevalence of QoI resistance in the northeastern United States, as well as the degree of orchard populations with the G143A mutation in the cytochrome b gene that confers a high degree of QoI resistance. With this understanding, attention is needed to understand the persistence of the G143A mutation in the absence of selective pressure. These studies contribute to the collective knowledge of how disease management options affect V. inaequalis DMI and QoI fungicide resistance.
Venturia inaequalis apple scab; DMI fungicide resistance; qualitative quantitative QoI
Cox, Kerik D.
Smart, Christine Durbahn; Fuchs, Marc F.
M.S. of Plant Pathology
Master of Science
dissertation or thesis