The aim of this project was to develop tool/s to inform grower decision making with regards to Verticillium wilt. Verticillium wilt is caused by the soil-borne fungal pathogen Vertillicum dahliae. Once introduced to a field, V. dahliae is considered impossible to eradicate. Failure to control the build up of disease inoculum can result in very large yield losses and fields becoming unsuitable for cotton production. Reports from growers estimate yield losses range from 10–62 per cent. As there are no control options for Verticillium, recommended best management is to rotate out of cotton to non-host crops until levels of V. dahliae. sufficiently reduce. Understanding the risk of verticillium disease prior to planting would mean growers could make informed decisions about whether it was safe to go back to cotton, potentially preventing significant yield losses.

Key outcomes:

- Diversity of V.dahliae virulence even within strains is quite high and some Australian isolates can cause more severe damage compared to international isolates.

- The development of a V. dahliae specific inoculum quantification assay was extremely challenging and semi-successful. The molecular soil assay can detect V. dahliae and the sensitivity of detection was 10-30 ppg in naturally infected soil. This is not sensitive enough when one propagule per gram of soil is enough to cause disease in more severe strains. A disease matrix was developed to industry that provides a guide to disease risk.

- A methodology was developed to determine the strain (VCG) of V.dahliae in soil using a combination of the dry plating soil assay and sequencing.

- A plant tissue molecular assay was developed that is faster than traditional isolating techniques and is capable of diagnosing V. dahliae and providing VCG in a higher proportion of infected plants. This molecular tool means industry has ability to quickly diagnose Verticillium down to VCG and growers and consultants can quickly determine which strain of V.dahliae they have, enabling Verticillium risk to be factored into decision to grow cotton.