| The role of greenhouse insects (Scatella stagnalis and Bradysia impatiens) in the introduction and spread of several Oomycetes that cause root-infecting diseases in greenhouse systems was evaluated. Results indicate that adult fungus gnats and shore flies are highly unlikely to serve as aerial vectors of Oomycetes. Larval stages of both insects can ingest and excrete viable oospores and/or conidia of Pythium aphanidermatum, P. splendens, P. sylvaticum, P. ultimum and Hyaloperonospora parasitica, as well as chlamydospores of Phytophthora ramorum. Transmission of sporangia by these insects did not occur. In vitro studies demonstrated that conidia and chlamydospores of P. ramorum, P. splendens, P. sylvaticum, and P. ultimum survived the digestive tracts of fungus gnat larvae and upon excretion infected both pepper seedlings and detached rhododendron leaves used as a bioassay at rates of 29% - 67%. Brown garden snails Helix (Cytoomyphalus) aspersa Muller ingested propagules of P. ramorum which upon excretion infected detached leaves. Both insect larvae and snails may play a role in pathogen introduction and/or dispersal of pathogen propagules via food webs.; Experiments demonstrated that coir has pathogen-suppressive properties which may be due to chemical compounds and/or microorganisms in coir. p-Coumaric acid, a known component of coir, reduced growth of Fusarium solani and Phytophthora capsici by up to 84% and 79%, respectively. A coir extract inhibited growth of Cladosporium cucumerinum in a TLC bioassay and reduced mycelial growth of F. solani by up to 80%. Mycelial growth of P. capsici on a non-filter-sterilized coir-leachate-mended media was almost completely inhibited regardless of leachate concentration. Water agar amended with non-autoclaved coir completely inhibited growth of F. solani. Aspergillus terreus recovered from coir inhibited mycelial growth of various soil-borne pathogens by up to 75%. Colony forming units of F. solani recovered from 100% coir and from root and crown tissues of gerberas grown in 100% coir were up to 85% and 79%, respectively, fewer compared to 100% soil. Results from this study indicate that coir has potential to reduce losses from soil-borne diseases in greenhouse and nursery production. |
