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Effect of paclobutrazol on laurel wilt on redbay (Persea borbonia) and the laurel wilt pathogen, Raffaelea lauricola

Stephanie Adams: The University of Florida & The Morton Arboretum

<div>Paclobutrazol belongs to the triazole group of DMI fungicides. Its fungicidal mode of action is as a sterol biosynthesis inhibitor, although it is more commonly used as a plant growth regulator in horticulture and arboriculture. Laurel wilt is a fatal disease of members of the Lauraceae caused by the fungus <em>Raffaelea lauricola</em>. Since <em>R. lauricola</em> was first identified in the United States in 2003 it has caused widespread death of redbay (<em>Persea borbonia</em>), swamp bay (<em>P. </em><em>palustris</em>), sassafras (<em>Sassafras albidum</em>), and more recently it has been found in avocado (<em>P. americana</em>).<br /="/"><br /="/">The effects of varying concentrations of paclobutrazol from 0-400 parts per million (ppm) have been tested <em>in vitro</em> on <em>R. lauricola</em>. Paclobutrazol has a fungistatic effect on <em>R. lauricola</em> at concentrations lower than 400 ppm and significantly slows the growth in concentrations less than 12 ppm. However, paclobutrazol does not appear to have fungicidal effects, as regrowth is observed once subcultured back onto unamended malt extract agar. <br /="/"><br /="/">How paclobutrazol changes the redbay host, by possibly changing physiological processes, tissue morphology, and disease response can help us understand resistance and susceptibility in the species better. This will contribute to future plant selection and breeding programs to mitigate the effects of this disease.</div>