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Abstract
Foliar damage symptoms to leatherleaf fern (Rumohra adiantiformis [Forst] Ching) in Florida during widespread use of the fungicide Benlate DF could not be attributed to nutrition, cultural practices, environmental conditions, or new pathogens developing on the crop. The objective of this study was to assess the involvement of rhizosphere bacteria in the damage symptoms using bioassays to detect phytotoxic activity. Rhizosphere bacteria were cultured from rhizospheres of leatherleaf ferns sampled from ferneries where Benlate DF was routinely applied and from check ferneries not receiving the fungicide. Using a lettuce seedling bioassay, the proportion of rhizosphere bacteria that was plant growth‐inhibitory ranged from 7.5% and 11% for isolates from two check ferneries to 70% for those from a fernery previously treated with Benlate DF. Rhizosphere bacteria originating from Benlate DF‐treated leatherleaf ferns caused most severe damage on seedlings with some isolates reducing root growth 70% compared to control seedlings. Other symptoms induced by these bacteria, which were mainly fluorescent and nonfluorescent pseudomonads, included necroses and inhibition of root hair development. Results suggested that Benlate DF affected the composition of bacteria in leatherleaf fern rhizospheres by promoting a bacterial component with phytotoxic properties toward plant growth.
Notes
Benlate ® is a registered trademark of E.I. duPont de Nemours & Co. Product names are necessary to report factually on available data; however, the University of Georgia, Lincoln University of Missouri, or USDA neither guarantees nor warrants the standards of the product, and the use of the name implies no approval of the product to the exclusion of others that may be suitable.