Potential sources of Pythium inoculum into greenhouse soils with no previous history of cultivation

A study was undertaken to investigate the potential sources of Pythium inoculum in greenhouse soils. About 7% of fallow soils were found to harbour Pythium before being introduced into greenhouses. When replacing the top layer (30-60 cm) of cultivated soil in greenhouses with fallow soil, Pythium inoculum was still recovered from the bottom layer of soil left in the greenhouse. Other potential sources of Pythium were found to be potting mixtures and contaminated soil adhering to cultivation equipment, growers' shoes and reused irrigation pipes. Pythium isolates from different sources were from two species: Pythium aphanidermatum (88%) and P. spinosum (12%). This appears to be the first report of transmission of Pythium via contaminated soil adhering to reused irrigation pipes. It also represents the first report in Oman of transmission of Pythium into greenhouses via potting mixtures and fallow soils.