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. Australian Sweetpotato Growers Inc. (ASPG) investigated how to improve productivity of on-farm multiplication nurseries (plant beds). Their four-year project also studied 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% of Australia’s production.
Queensland scientists monitored grower plant beds over four years, assessing production of planting material (sprouts), and problems, such as plant bed breakdown, that arose during the season. 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 virology team surveyed viruses present in the Australian industry, and how they varied geographically and across the season. They compared different diagnostic techniques, including herbaceous indexing, NCM-ELISA and qPCR for accuracy and cost-efficiency.
Research demonstrated sprout multiplication could be improved 25% by constructing higher, well-drained plant beds, only covering bedding roots with 3-5 cm of soil, irrigating sparingly early, and keeping soil temperatures between 17-26oC in spring by careful use of plastic covers. The dominant issue was premature plant bed breakdown, particularly with the new, nematode-resistant cultivar Bellevue. The project investigated physiological and pathogenic causes of breakdown and developed guidelines to reduce risk.
Surveying found only two main viruses, sweetpotato feathery mottle virus (SPFMV) and sweetpotato leaf curl virus (SPLCV) in commercial cropping areas. North Queensland has two more viruses at least, mainly in home/market garden situations. The Australian industry planting material scheme is free of viruses, and by using pathogen-tested material, virus infections have negligible impact on yields.
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 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.
The project team prepared plant bed and virus management guides, as well as fact sheets and experimental reports, available on ASPG and Hort Innovation websites. They had excellent engagement with well over 85% of current Australian sweetpotato growers, through on-farm visits, and 24 field days and workshops during the project. The project also developed exciting collaborative relationships with sweetpotato researchers at several Australian Universities, neighbouring Pacific countries, and particularly scientists from Louisiana State University. The latter were involved in several reciprocal visits over the four years.
Further research into the causes and management of premature breakdown of plant beds would certainly benefit the Australian industry, as would improvement in molecular diagnostic assays for virus detection, to support sweetpotato industry biosecurity.
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