Audio, summary and presentation (Spanish – English) of the lecture that Richard Falloon, New Zealand Institute for Plant & Food Research Limited – Lincoln, presented at the XXVI Biennial Congress of the Latin American Potato Association (ALAP) in Bogota (Colombia).

 
Spongospora subterranea causes powdery scab of potato tubers, an important disease problems for all sectors of potato industries, including seed tuber production, and where crops are grown for fresh markets or for processing.

The pathogen also infects potato roots, a stage that is increasingly recognised for harmful effects on plant growth and productivity, and as the source of rapid increases in soil inoculum.

Recent research has confirmed that S. subterranea probably originated from South America. The pathogen has spread throughout the world, most likely from Europe, as potato has been widely adopted for food production in temperate climates, as the international trade in seed potatoes has expanded, and as potato production has become increasingly intensified.

Spongospora zoospores, produced from long-living resting spores in sporosori, infect the roots of young potato plants. Zoospore multiplication and infection cycles follow and are probably responsible for harmful effects on host growth. Infections of host roots later develop into galls which mature to release many sporosori into the soil. Stolon infections develop as powdery scab lesions on tubers, which also contain many sporosori.

Lesions on tubers reduce their quality for fresh market sale and for processing, and the disease on seed tubers is a likely source of transmission of the pathogen to future crops.

The pathogen is also the vector of Potato moptop virus, an important quality-limiting virus. Sporosori and resting spores can survive for many years, posing severe problems where potatoes are grown in short crop rotation cycles.

Several control methods have been tested as possible management options for Spongospora diseases of potatoes. Long crop rotation intervals are recommended between potato crops where powdery scab has previously occurred, and “biofumigant” crops may reduce soil inoculum levels.

Soil- or seed tuber-applied sterilants and pesticides have been shown to reduce disease incidence and severity, but these are increasingly unacceptable in modern food production systems.

Manipulation of soil environments with nutrient applications (e.g. zinc, boron, ammonium nitrogen, elemental sulphur), have been shown to reduce powdery scab on harvested tubers, and irrigation management to avoid excessive soil moisture during tuber initiation may reduce the disease.

Some potato cultivars are much less susceptible to powdery scab than others, so if cultivar choices are available, those that are resistant to the disease should be grown.

Utilising effective host resistance to all stages of the pathogen life cycle (on roots and tubers) is likely to be the most acceptable and “sustainable” strategy for effective management of the economically important potato diseases caused by S. subterranea.

Like many soil borne diseases, those caused by S. subterranea pose severe problems for potato growers aiming to produce high-qua- lity and high-yielding crops. Effective disease management is likely to be best achieved across all stages of crop management, using multiple disease control strategies.

Solutions to the problems caused by S. subterranea require continued research effort, across the crop production and cultivar development science disciplines.

Image: South Australian Research and Development Institute – SARDI

Falloon, Richard 1,2 and Merz, Ueli 3
1 New Zealand Institute for Plant & Food Research Limited, Lincoln, New Zealand.  E-mail: richard.falloon@plantandfood.co.nz

2 Bio- Protection Research Centre, Lincoln University, Lincoln, New Zealand
3 Plant Pathology, ETH Zurich, Switzerland

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