Impact of environment, plant morphology, and resistance genes on disease severity of downy mildew in lima bean in Delaware
Date
2021
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University of Delaware
Abstract
Lima bean is the cornerstone crop of the Delaware vegetable processing industry and a major source of income in the mid-Atlantic region (MAR) as a whole. Lima bean is planted mid-summer and harvested during early fall. Unfortunately, the cool, humid conditions near harvest provide conducive conditions for the destructive oomycete pathogen, Phytophthora phaseoli, the causal agent of downy mildew of lima bean. Control options utilized by growers include using resistant cultivars and preventative/curative oomyceticide applications, though both have drawbacks. Currently, physiological race F of P. phaseoli is dominant in MAR lima bean fields. It is unclear whether race E is still present, and there are no commercial cultivars resistant to both races. Oomyceticides, although useful, are expensive and often select for resistant individuals. Research has been conducted on alternate methods of disease inhibition, including altering leaf shape and architecture, probing new sources of race E/F resistance, and applying regiments of red light, all with the express purpose of stopping downy mildew of lima bean. Results have shown applications of red wavelengths of light and thinner lanceolate leaf shapes both correspond to lower disease severity. In addition, new sources of resistance have been uncovered, though their apparent recessive natures were not expected. Continued research on these disease inhibition methods is needed, however, results of this project indicate potential for implementation into the commercial grower’s disease toolbox to allow for healthier, cheaper lima beans.
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Keywords
Leaf shape, Leaf architecture, Mildew resistance, Red light