What was it all about?

The provision of disease-free planting material is a key driver of Australia’s burgeoning sweetpotato industry, which currently achieves the highest commercial yields in the world. Beginning in 2014 and recently concluded, this project investigated how to improve the productivity of on-farm multiplication nurseries (plant beds). It also involved the study of virus occurrence and threats to the Australian industry, and explored new techniques for detecting viruses. The project worked closely with commercial sweetpotato growers in Queensland and northern New South Wales, representing 95 per cent of Australia’s production.

Queensland scientists monitored grower plant beds over the investment’s four years, assessing production of planting material (sprouts) and problems, such as plant bed breakdown, that arose during the seasons. They investigated management options such as sweetpotato root size, plant bed nutrition, irrigation and soil temperatures, in detailed experiments at research facilities and with on-farm collaborators.

The project’s virology team surveyed viruses present in the Australian industry and how they varied geographically and across the season. They also compared different diagnostic techniques for accuracy and cost-efficiency.

The research demonstrated that sprout multiplication could be improved as much as 25 per cent by…

• Constructing higher, well-drained plant beds
• Only covering bedding roots with 3-5cm of soil
• Irrigating sparingly early
• Keeping soil temperatures between 17-26°C in spring by careful use of plastic covers.

The dominant issue seen was premature plant bed breakdown, particularly with the new, nematode-resistant cultivar Bellevue. The project investigated physiological and pathogenic causes of this breakdown and developed guidelines to reduce risk (see the ‘act now’ section below to download these and other project resources).

Surveying found only two main viruses, sweetpotato feathery mottle virus (SPFMV) and sweetpotato leaf curl virus (SPLCV), in commercial cropping areas. The researchers report that north Queensland has two more viruses at least, mainly in home/market garden situations. However the Australian industry planting material scheme is free of viruses, and by using pathogen-tested material, virus infections have negligible impact on yields.

Regarding diagnostics, ‘herbaceous indexing’ with Ipomoea setosa is still the most reliable method of detecting sweetpotato viruses, but is very time consuming. Molecular technologies such as qPCR proved accurate for two viruses, however for several endemic and exotic viruses, current assays produced too many false negatives, particularly testing asymptomatic sweetpotato material. The researchers report, though, that molecular technologies are very cost-effective and are rapidly improving. The project developed new virus assays for endemic and exotic viruses not currently in Australia.

In addition to its research work, during the course of the project the researchers were involved in 24 industry field days and workshops to help communicate project activities and findings to growers. The project also developed collaborative relationships with sweetpotato researchers at several Australian universities, neighbouring Pacific countries, and particularly scientists from Louisiana State University in the US. The latter were involved in several reciprocal visits over the project’s four years.

ACT NOW

The project produced a range of fact sheets and guides for Australian sweetpotato growers, downloadable below:

• Managing sweetpotato viruses in Australia: grower guide (2018 edition)
• Managing sweetpotato plant beds in Australia: grower guide (2018 edition)
• What is sweetpotato chlorotic stunt virus?
• Australian sweetpotato pathogen testing procedures (2018 edition)

Further resources relating to the project, including student honours theses out of the research, are available on the Australian Sweetpotato Growers website here.