Poster Presentation Science Protecting Plant Health 2017

Pythium species Associated with Yield Decline in Processing Tomatoes in Victoria (#211)

Sophia E Callaghan 1 , Paul Taylor 1 , Lester W Burgess 2 , Liz Mann 3 , Ann Morrison 3
  1. The Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville, VICTORIA, Australia
  2. Sydney Institute of Agriculture, The University of Sydney, Australian Technology Park, Eveleigh, NSW, Australia
  3. Australian Processing Tomato Research Council Inc., Shepparton, Victoria, Australia

The Australian Processing Tomato Industry (APTI) is based primarily in the Goulburn Valley in northern Victoria, extending into southern NSW. The field-grown tomatoes are produced as an irrigated summer crop and are often grown successively in the same field for 4-5 years before being rotated for 1 year with a cereal or corn crop. The tomatoes are grown from transplants or seed with sub-surface tape irrigation following soil treatment with metham sodium. Following the 2015/16 season, the Australian Processing Tomato Research Council (APTRC) estimated that the industry had lost 10-15% of yield and considered that diseases caused by soil-borne pathogens might be a contributing factor.

In autumn 2016, a glasshouse pot bioassay was performed whereby tomato seedlings were grown in three similar types of field soil, two with a recent history of tomatoes and evidence of yield decline, and one with no history of tomatoes. After 6 weeks, root lesions had developed on the root systems of plants growing in the two soils with suspected yield decline. A Pythium species, confirmed by culture morphology and ITS gene sequence, was consistently isolated from diseased roots. The pathogenicity of the Pythium sp. to tomato seedlings was confirmed with 100% of inoculated seedlings dying from damping-off.

Five field surveys were completed across the 2016/17 season and isolations were made from root lesions, and from the discoloured inner crown tissue of stunted plants. Over 200 isolates of putative Pythium species were recovered, together with approximately 300 isolates of putative Fusarium oxysporum. Phytophthora nicotianae, Sclerotinia sclerotiorum and Colletotrichum sp. were also isolated at a lesser frequency. Further studies using multigene phylogenetic analysis are underway in order to identify the Pythium species. Their pathogenicity is being assessed in greenhouse studies.