A Protocol for Isolating and Enumerating Thielaviopsis basicola From Cotton Roots: Applications to LONREN Stunt

Thielaviopsis basicola is a slow growing fungus that is easily overwhelmed by bacteria and other fungi when whole tissues are plated on media.  Developing selective media is complicated by sensitivity of the fungus to many antibiotics.  A selective medium was developed, that allows ready recovery of the fungus from diluted fine tissue particles produced from surface sterilized roots by a polytron tissue generator.  Dilution series of dispersed particles with drop applications to media allows determination of colony forming units (cfu) per gram of fresh root tissues.  Transplanting 48-hour-old seedlings into soils and analyzing roots after 5 to 7 days shows the inoculum potential of soils.  This protocal and its application to studies of the cause of stunting of LONREN cotton lines in reniform infested fields will be presented in detail.