Distribution and season-long monitoring of Pythium species affecting Zea mays in Delaware
Date
2021
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Publisher
University of Delaware
Abstract
Corn (Zea mays L.), is a valuable cash crop for the state of Delaware planted across 71,225 hectares annually with a production value over $121.1 million. In annual disease loss estimates, root rot and death of plants due to Pythium infection is one of the top yield-limiting factors in Mid-Atlantic corn production. Across the United States and Ontario, estimates indicate that at least 238 million bushels of corn were lost due to root rots and seedling blights within the four-year span of 2016 to 2019. While multiple organisms can be involved in root rot and seedling blight diseases, Pythium is one of the most frequently associated pathogens. This oomycete organism is found worldwide affecting corn almost anywhere wet, waterlogged soils or high humidity growing conditions exist. The genus Pythium contains hundreds of species, most of which have been shown to be aggressive plant pathogens. To date, forty-four Pythium species have been associated with corn in the United States. Limited research has been conducted to elucidate the distribution of species, fungicide sensitivity ranges, and growth effects of Pythium isolates infecting corn in the Mid-Atlantic. In this thesis, surveys were conducted in 2019 and 2020 to molecularly characterize Pythium species present across Delaware and screen for fungicide sensitivity and aggressiveness of collected species. On-farm observation trials were established to document season-long effects of early season Pythium infection. From the survey, 14 species of Pythium were identified among the 367 isolates collected representing three clades. A subset of five species tested were found to be sensitive to mefenoxam, ethaboxam, and picarbutrazox, with the exception of Pythium torulosum, which showed reduced sensitivity to ethaboxam. A larger panel of 12 species were tested for temperature and fungicide interactions, where increasing temperature reduced inhibition of multiple Pythium species on fungicide amended media. Season-long tracking of Pythium infected plants compared to nonsymptomatic control plants showed significant reductions of stalk flexural rigidity, stalk circumference, root mass, and kernel count. This work serves as a foundation to improve understanding of pathogen biology to better manage disease loss in Mid-Atlantic corn production.
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Keywords
Corn, Delaware, Fungicide, Oomycete, Pythium