What was it all about?

This investment, which ran from 2017 to 2020, has broadened the understanding of powdery scab suppression in field soils and this information will be used to inform future management strategies for diseases caused by Spongospora subterranean. The research team has confirmed that some soils have characteristics that suppress Spongospora diseases of potato and identified some of the mechanisms of suppression.

Powdery scab reduces the quality and marketability of seed, fresh market, and processing potatoes. The pathogen Spongospora subterranea causes severe galling on potato roots and disrupts uptake of water and nutrients in actively growing plants, reducing tuber yields.

The research team focused on field soils from the South Auckland/Waikato region of New Zealand, including Pukekohe, a location where a previous long-term field trials have demonstrated very low amounts of powdery scab developing in susceptible potatoes. This suggested that the trial site soil may be ‘suppressive’ to the powdery scab pathogen.

The research included three greenhouse pot experiments, where different field soils were assessed for their physical, chemical and biological characteristics, and for their sensitivity to potato root hyperplasia (galling) and tuber powdery scab caused by S. subterranea. The work was carried out in three phases, during 2017/2018 (Phase 1), 2018/2019 (Phase 2), and 2019/2020 (Phase 3; project extension).

The experiments confirmed that some soils were more suppressive than others to root galling and tuber powdery scab. Suppression of Spongospora diseases was shown to be locally specific. Soil texture, and especially soil drainage, influenced powdery scab incidence and severity. Abiotic soil factors such as texture, organic matter content, acidity, and nutrients influenced incidence and severity of Spongospora root galling and tuber powdery scab on potato plants. 

Soil microorganisms were shown to be involved in disease suppression; when they were eliminated or reduced by soil heat treatment, powdery scab incidence and severity increased. Bacteria and funguses may play roles in Spongospora-suppressive soils, but these were not identified.

The project team found that potato plants grown in field soils containing high levels of manganese developed less severe Spongospora diseases than plants grown in soils with low levels. Applications of manganese to soil and potato foliage reduced powdery scab in naturally low manganese soils. However, additions of manganese to soils with ‘normal’ to very high natural levels did not affect the disease.

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Read about the research to understand how different field soils affect the development of powdery scab on potatoes in this article, Do some potato growing soils suppress powdery scab?, published on pages 24-25 of Potatoes Australia magazine, June/July 2018.

Read about the farmers supporting research into powdery scab in potatoes in New Zealand in this grower profile, Bryan Hart: Fighting the powdery scab battle, published on the AusVeg website in December 2018.