Pathogen-tested Sweet potato germplasm for the South Pacific

• Department of Primary Industry, Papua New Guinea
• University of the South Pacific, Samoa
• Ministry of Agriculture and Forestry, Tonga

Sweet potato is a major food crop in several South Pacific countries: it provides the staple food of Papua New Guinea and the Solomon Islands, has importance in Tonga and Vanuatu and is generally gaining in popularity is the region. Local breeding and selection programs to improve the quality of the crop have begun, but the presence of virus diseases and other pathogens hinders the acceptance and distribution of the emerging new cultivars. Papua New Guinea maintains major and diverse collections of sweet potato that will provide potentially valuable germplasm to breeders throughout the region. So too will a breeding program established in Tonga by IRETA (Institute for Research, Extension and Training in Agriculture) from the University of the South Pacific, Samoa. This program aims to provide cultivars with resistance to the scab disease caused by the fungus Elsinoe batatus. which causes large economic losses each year.

Eradication of pathogens from this valuable germplasm will enable proper screening and assessment of the material for yield potential, disease resistance and other qualities, exchange of material between countries and tbe development of facilities for rapid multiplication of pathogen-tested stocks to improve local sweet potato cropping. The Plant Research Institute (PRI), which operates pathogen-tested schemes for several vegetatively propagated crops, has the facilities and expertise for such work.

Initially, this project will emphasise cultivars selected by agronomists and breeders in Papua New Guinea and the Pacific Islands. They will identify superior sweet potato cultivars and document their characteristics. The project will also identify non-Pacific cultivars with potential value in the region. Scientists at PRI will collect elite cultivars and identify major virus and mycoplasma diseases, eradicating the pathogens by heat treatment and meristem-culturing. They will carry out virus indexing, and maintain and distribute pathogen-tested cultivars. At an early stage of the project, they will train personnel from participating countries in the techniques of rapid multiplication, assisting them to develop suitable facilities, and will disseminate relevant information. This work will include preparation of a booklet on the handling of tissue cultures and their transfer to soil, maintenance of pathogen-tested plants to reduce reinfection rates and evaluation of materials.

While scientists from the participating countries will conduct the agronomic trials there, PRI staff will assist in the planning and assessment of the field trials. They will cover, in particular, aspects of statistical design and analysis of field experiments and the monitoring of rates of reinfection by pathogens, including viruses, MLOs and root knot nematodes. To determine rates of virus spread, they will prepare ELISA plates and electron microscopy grids, which will be returned to PRI for processing.

In selecting elite cultivars for clean-up, the team will emphasise yield potential, resistance to weevil, leaf scab, little leaf and virus diseases and high nutritional value; as well, they will ensure a range of plant types for various cropping systems.