Mechanisms and manipulation of resistance to powdery scab in potato roots (PT17003)
What’s it all about?
While the potato tuber blemishes that are caused by powdery scab are a concern for the potato industry, the pathogen’s effect on plant roots can’t be underestimated, either. Root infection with powdery scab disrupts root function – meaning more irrigation, fertiliser and fungicides are needed to compensate for poor root development – and leads to diminishing yields.
In this project, researchers are investigating root resistance to powdery scab infection. This involves looking at how the pathogen infects roots and causes disease, what allows for resistance in some potato varieties, and whether resistance mechanisms may be boosted or transferred.
While caused by the same pathogen, the powdery scab root and tuber infection processes are separate, and different plant resistance processes operate against each. This means that varieties that show resistance to tuber disease don’t necessarily show resistance to root infection. However, when root infection is decreased, disease across the whole plant is slowed, meaning tuber disease is reduced as well.
Receptor blocking/disruption trials were completed after testing roots and root hairs with four different enzymes to identify the nature of any receptor. Further enzyme treatments are being discussed as a small extension to this work.
DNA extraction and analysis of genotyping populations has commenced with DNA from the mapping population sent to the NZ collaborators. DNA has been processed and SNP markers generated.
Variant glasshouse testing commenced, with five lines selected that showed promise for reducing root attachment. These selected variants (Russet Burbank (10 lines); Ranger Russet (11 lines); Desiree (24 lines); Sebago (5 lines); Shepody (3 lines)) have been planted out in a set of replicated glasshouse experiments which aim to be completed by mid-2022. The experiments will challenge all lines with S. subterranea soil-borne inoculum as well as assess relative resistance to root and tuber disease and a crude tuber yield assessment.
Industry engagement continued, with Oral and written industry presentations at annual program forum, industry days and in industry magazines (Potato Australia, Potato Link). Access the Potato Link and Potato Australia (AUSVEG) magazines.
The project team reports the following progress:
- Receptor blocking / disruption trials continued, with work undertaken to better understand the nature of root receptors and interfere with zoospore binding in
- Variant in vitro testing was completed on seven target cultivars, demonstrating significant variation in susceptibility to zoospore binding. Several lines showed improved resistance to the pathogen, with some additional cultivars now being screened. The team will select those showing the most promise for replicated glasshouse pathogen trials to determine whether the enhanced disease resistance phenotype is expressed in both roots and tubers, and make an initial assessment of relative growth and yield.
- Mapping population phenotyping of potato germplasm from Australia (160 lines) was completed, with a good spread of resistance rating (from 1.6 to 12.9) across diverse genetic background, providing a sound basis for subsequent analysis
- Industry engagement continued, with a presentation of project outcomes to date planned as part of the annual program conference to be held in late July/early August 2021.
In the second year of this project, the team report progress in the following areas.
- A full cultivar screening validation trial was completed. Disease levels were insufficient to adequately differentiate between all cultivars, likely due to less than expected inoculum presence and a hot spring during the early trial period. The team intend to repeat this trial in autumn once temperatures can be maintained at a disease conducive level.
- Variant in vitro testing commenced with successful variant selection of the seven target cultivars (Desiree, Nicola, Sebago, White Star, Russet Burbank, Russet Ranger and Shepody), before propagation in tissue culture for initial test sets. Early results indicate evidence of variation amongst clones in zoospore attachment rates. Once the full tests are complete, the team will focus on those showing promise for resistance for further evaluation.
- The cultivar resistance list was circulated, with additional varieties to be tested and included as they become available.
- Receptor blocking/disruption trials were started, to better understand the nature of root receptors and interfere with zoospore binding. The first of these experiments utilises a technique known as trypsin shaving, which allows the team to refine root protein datasets and test the effect of protein disruption on zoospore binding.
- The DNA extraction and analysis of mapping populations (from Tasmania) commenced, despite COVID-19 restrictions requiring a change of approach to gaining access to cultivar material. The team have negotiated to access collections of potato lines from around Australia, providing sufficient statistical power to analyse gene markers for the root binding phenotype.
Preliminary studies have shown that reduced root binding by zoospores is correlated with reduced disease and yield loss and that potato cultivars vary, with some showing reduced binding and subsequent infection. However, virtually nothing is known about the nature of the root binding sites and the basis of this resistance.
To date, the project team have progressed the following research activities:
- The root surface protein study and variant resistance screening has commenced, with the preferential binding sites across susceptible and resistant cultivars being determined which provides a target region for examination of root surface proteins.
- Screening of the test cultivars has been conducted to ascertain efficiency of differentiation of susceptible and resistant cultivars. Screening of the large variety collection has commenced and will take two to three months to complete.
- Project team members attended an international symposium on Spongospora disease research in September 2019 to present information about the project and hold collaborative technical discussions aimed at progressing project outcomes.
- Aspects of the project were presented to an audience of 113 industry members at the Forthside Tasmanian Institute of Agriculture Vegetable Facility Open Day held in December 2019.
Next steps for the project team are to:
- Determine the nature of spore root attachment
- Characterise cultivars for this important type of resistance
- Examine the capability of manipulation of attachment sites through binding blockers or similar approaches
- Develop and screen variants of important commercial cultivars that have altered root attachment capacity, and analyse these for genetic changes associated with reduced binding that will be useful for rapid screening of new germplasm.