International partnerships transforms sweet potato industry in Australia and Papua New Guinea

By the Australian Centre for International Agricultural Research

Sweet potato growers in the remote highlands of Papua New Guinea (PNG) and in the fertile farmlands of Australia might seem to be worlds apart. However, they share an intense interest in a common enemy: plant viruses.

Now, a long-standing partnership between researchers in Australia, PNG and Peru, supported by the Australian Centre for International Agricultural Research (ACIAR), is providing them with a shared solution, in the form of disease-free planting material.

Sweet potato is the main staple food of PNG, supplying some two-thirds of the country’s basic calorie needs. However, as the country’s population has grown, especially in the densely populated highlands, the productivity of this vital food-crop has faltered. The decline in yields was variously attributed to falling soil fertility or increasing pest pressure, but work that began in 1984 increasingly showed that plant viruses were a key factor.

Plant viruses cannot reliably be identified by symptoms alone, so in 2004 researchers from Queensland’s Department of Agriculture and Fisheries (Q-DAF) teamed up with their counterparts at PNG’s National Agricultural Research Institute (NARI) and the International Potato Centre (CIP) in Peru to develop diagnostic tests. The partnership continues to this day, with CIP providing early warning of new viruses at the global level (and tests to detect them) while researchers in Australia and PNG monitor continuously for new virus threats closer to home and develop the tests to identify them.

The nerve-centre of this surveillance effort, supported jointly by Q-DAF and ACIAR, is Gatton Research Station, outside Brisbane, where Sandra Dennien monitors disease samples collected from farmers’ fields across the region.

In PNG, the NARI team maintains disease-free sweet potato stocks in an insect-proof screen-house at Aiyura Research Station

Viruses of sweet potato, like those of various other crops, can be eliminated from the plant by heat treatment, ‘thermotherapy’, which differentially affects the rate at which plant cells and virus particles replicate. If it is done judiciously, virus-free plant cells can be retrieved from the growing point and multiplied through tissue culture to generate disease-free plants.

These can then be multiplied vegetatively, mainly by cuttings maintained in screen houses, where fine mesh excludes the insects (mainly aphids and whiteflies) carrying the viruses that would otherwise reinfect the plants.

Thermotherapy, though simple in principle, can be tricky in practice. The varieties of sweet potato most popular in PNG proved quite sensitive and initially died under the heat treatment. Persistence paid off, however, and some ten years ago NARI researcher Dorcas Homare managed to get the treatment ‘just right’ and, with the help of tissue culture specialist Winnie Maso, recovered disease-free sweet potato plants.

Since then, NARI’s Aiyura Research Station has provided a steady stream of ‘PT’ (pathogen-treated) or klin cuttings (’clean’ in local pidgin). Specially trained farmers then further multiply the material, as a small business, to provide enough klin cuttings for the thousands of other smallholder sweet potato farmers.

The most recent ACIAR project, on this occasion funded by Australia’s Department of Foreign Affairs and Trade, seeks to scale up the technology to provide a ‘clean seed system’ to support the transformation of sweet potato in PNG from subsistence crop to a full-scale commercial enterprise.

Meanwhile in Australia, PT technology has been enthusiastically adopted by the sweet potato industry. A pioneer in this effort has been Eric Coleman, a researcher-farmer who turned this experimental procedure into a commercially viable enterprise. Most Australian sweet potato farmers now plant their crop with PT material.

As Mike Hughes, a Q-DAF researcher and veteran of the ACIAR projects in PNG and Queensland, explains: “This essentially simple technology has transformed the sweet potato industry in Australia and is now set to play an equally important role for this vital crop in PNG.

 

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