Extension of the PreDicta Pt potato diagnostic service (PT15008)
What’s it all about?
Beginning in mid-2017, this project is responsible for expanding the PreDicta PT testing system to help minimise the impact of soilborne and seedborne diseases on Australian potato businesses.
Running since 2013, PreDicta Pt is the commercial DNA-based testing service that allows specific pathogens to be identified prior to the planting of potatoes. Available through accredited providers in the south-eastern states, the test results help identify and manage risks related to powdery scab, black dot and root knot nematode.
This project is expanding the service into other major production areas of Australia, adding new soil tests, and giving potato growers access to testing on seed tubers.
In the third and final year of this project, training of agronomists continues across the country. PREDICTA Pt is delivered through a network of accredited agronomists, with 51 participants added to this group since project commencement.
Demand for PREDICTA Pt has increased across the seed, processing and fresh sectors, with the number of samples from growers in 2018 up 25 per cent on previous years. To date in 2019, sample numbers are tracking 18 per cent higher than 2018.
New and existing tests are being trialled over a wider range of environments with recent progress in the following areas.
Verticillium wilt caused by Verticillium dahlia causes yield loss of potatoes across Australia. Symptoms are not always clear and disease impact can be underestimated. Inoculum in the soil is the main source of disease for potato crops.
Sufficient information has now been obtained to establish risk thresholds for the PREDICTA Pt V. dahlia test. This will assist growers to better manage this challenging disease in the short and long term. Seed tubers can also be tested, as infection can be of concern if planting potatoes in paddocks free of V. dahlia.
Potato cyst nematode
DNA based assays previously developed by SARDI for Globodera pallida (pale potato cyst nematode) and G. rostochiensis (golden potato cyst nematode) were evaluated by this project’s team to determine the detection limits, which is critical information for biosecurity use of the test.
Silver scurf caused by Helminthosporium solani is mainly of concern for fresh market potato growers. Inoculum on seed tubers is the main disease source. A test was developed for H. solani and evaluated to test peel samples from seed tubers. The results show the test provides a useful indication of infection risk of daughter tubers. This test will be an important addition to the PREDICTA peel testing service under development.
As shared in previous project updates, you can learn more about the PREDICTA Pt service and how it supports potato production decisions in this InfoVeg TV episode available online.
Validation of new DNA tests for soil borne pathogens, including pink rot, silver scurf and sclerotinia rot is underway. DNA testing delivers the ability to evaluate infection levels of multiple pathogens at any point during crop growth.
Trials are being conducted to enhance the ability to interpret results from DNA tests and other tests under evaluation, such as for the pathogens that cause potato early dying, rhizoctonia and common scab. These trials include using PREDICTA Pt to test paddocks before planting, followed by in-crop and harvest assessments for disease incidence and severity, and crop productivity.
Peel sampling and handling protocols for commercial testing services have now been finalised, specifying drying of potato peel samples for testing. Investigation into low cost drying systems has confirmed that off the shelf equipment can used.
PREDICTA Pt tests are being used to provide insight on infection levels of pathogens such as root lesion nematodes where visual assessment is of limited value. In the case of these nematodes, strong relationships are being found between pre-plant nematode populations and root infestation through the growth phase of the crop.
PREDICTA Pt technology allows identification, confirmation and quantification of observed soil borne diseases and, partly due to the work of this project, more growers and agronomists are using it. Previously, testing was mainly done by seed producers and processing sector between July to October, but now clients throughout Australia in all sectors of the industry are conducting testing fortnightly throughout the entire year.
Intensive soil sampling strategies have revealed that signs of pathogens in soil vary across a season, which means that when a test is made affects the outcome. For example, levels of pink rot inoculum in the paddock can drop rapidly to low levels after harvesting of an infected crop. This has prompted a change in sampling strategies to ensure the usefulness of testing.
Training of agronomists continues to extend the geographic range over which the PREDICTA Pt service can be accessed. By adding new tests and enhancing knowledge on existing tests over a wider range of environments, this project will deliver benefits to a greater proportion of the industry.
Entering the third and final year of the project, the focus is now on analysing the data generated and incorporating new knowledge, to enhance the value of the PREDICTA Pt service.
The most recent work in the project involves new trials to develop a protocol for sampling and handling potato peel samples for a new PreDicta PT peel-testing service. The research team report that packaging processes and additives to the peel have been studied as methods to stabilise pathogen DNA levels in the sample during transport from the grower to the processing laboratory, with work here ongoing.
Other project developments have included the establishment of field trials to validate a range of new and existing pathogen DNA tests, including developing ‘risk thresholds’ for the existing tests, which are currently reported without an indication of the disease risk they pose.
For this, pre-plant soil samples were collected from potato paddocks across South Australia, Victoria and Tasmania, along with seed tubers to look at the level of existing inoculum using pathogen DNA testing. In selected paddocks, stems, roots and tubers were also collected during crop growth to assess disease incidence and to understand pathogen build-up. In South Australia, the focus was on verticillium wilt and potato early dying. In Tasmania, the primary focus was on pink rot and rhizoctonia. Work here is also ongoing.
Meanwhile, as reported in the last edition of Hortlink, initial achievements of the project included the development of a new pathogen DNA test for pink rot. Pink rot is a serious fungal disease that infects all below-ground parts of the potato plant, causing a leathery look to infected tubers, which turn a characteristically pink colour, and eventually black, when cut.
The new test developed by the project detects three species of phytophthora that are known to cause pink rot. The process of evaluating the test’s use as a pre-plant soil assessment for the risk of pink rot developing remains underway.
Watch this video for a quick overview of the existing PreDicta PT service, produced as part of the industry’s communications program.
In its first six months, the project’s most significant achievement has been the development of a new pathogen DNA test for pink rot. Pink rot is a serious fungal disease that infects all below-ground parts of the potato plant, causing a leathery look to infected tubers, which turn a characteristically pink colour, and eventually black, when cut.
The new test developed by the project detects three species of phytophthora that are known to cause pink rot. The process of evaluating the test’s use as a pre-plant soil assessment for the risk of pink rot developing has now begun.
As well as developing new tests, the project aims to introduce a commercial service for quantifying pathogen levels in the peel of seed tubers, and to develop risk thresholds for existing pathogen tests that are currently reported without an indication of the disease risk they pose. Field validation trials will be conducted to confirm and or refine knowledge to interpret the tests.
It is also delivering training workshops for agronomists.