Artificial Inoculation of Crop Species in Australia with Fusarium oxysporum f.Sp. Vasinfectum

Justification and objectives
Fusarium wilt of cotton remains an economic constraint to cotton production in Australia since its identification in 1993.  The pathogen, Fusarium oxysporum f.sp. vasinfectum (Fov) survives as spores in the ground, saprophytically on residues or on alternative hosts.  While there are a number of known symptomless weed hosts, the extent to which Fov can infect and multiply on rotational crops in Australia has not been determined.  The aim of this preliminary study was to determine infection and colonisation of rotation crops following artificial inoculation. 

Materials and methods
Seeds of twenty four different crops were planted into small pots containing sterilised potting mix.  At three weeks of age the seedlings were inoculated by removing from pots and dipping roots in a spore suspension of a known Australian VCG 0-1111 isolate of Fov for six minutes (spore concentration was 1.5 x 10⁶ spores per ml).  Re-potted plants were grown in a glasshouse with an approximate temperature range of 18-25ºC for six and a half weeks.  Plants were washed to remove potting mix and surface sterilised prior to plating root/crown and stem material onto half-strength PDA amended with streptomycin sulfate.  To fulfil Koch’s postulate pathogenicity tests were set up to inoculate cotton seedlings with the recovered isolates and confirm the presence of Fov. 

Results
All crops tested, except one yielded Fov, largely without symptoms.  The extent of infection up the stem varied between crop species.