Elucidation Of The Role Played By Fungus Gnats (Diptera: Sciaridae) In The Transmission Of Pythium Root Rot Diseases Of Floriculture Crops
Fungus gnats of the genus Bradysia (Diptera: Sciaridae) are ubiquitous pests in greenhouse crop-production systems. Because of their association with decaying vegetation, fungus gnats are commonly found to coexist with diseased plants, and their role as vectors of plant pathogens has been questioned for decades. Studies have demonstrated that adult fungus gnats can acquire and mechanically transmit aerial spores of various fungal plant pathogens. However, a significant role in the transmission of pathogens that do not generate large numbers of readily transmissible propagules has not been demonstrated. The ultimate objective of this dissertation was to elucidate the role played by fungus gnats, Bradysia impatiens (Johannsen), in transmission of Pythium spp. to floriculture crops. Fungus gnat adults strongly preferred to lay their eggs on plant material infected/infested with a wide array of microorganisms, including Pythium, Thielaviopsis, Trichoderma, Beauveria, and Xanthomonas. Although fungus gnats were highly attracted to microbial activity, adults are unlikely crop-to-crop or greenhouse-togreenhouse vectors of Pythium root rot pathogens. Studies revealed that adult fungus gnats do not pick up or transmit infectious Pythium propagules from diseased to healthy plants. Furthermore, adult gnats do not likely carry Pythium internally as they are generally described as aphagous, and experiments revealed that Pythium ingested by fungus gnat larvae is not carried beyond the pupal stage. Larval fungus gnats are capable of vectoring some species and strains of Pythium in the laboratory, although this slow-moving life stage is unlikely to account for significant transmission of Pythium spp. in the greenhouse setting. Feeding damage by fungus gnat larvae induced resistance to Pythium infection, significantly reducing seedling mortality compared with undamaged controls. The findings from these studies enhance our understanding of the association between fungus gnats and Pythium in greenhouse floriculture.
Sanderson, John P
Wraight, Stephen Paul; Nelson, Eric Bronson
Ph. D., Entomology
Doctor of Philosophy
dissertation or thesis