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Sweet Potato

Content
Technology Release of Sweet Potato Varieties for the Lowlands
Type of Release
Evaluation of Sweet Potato Varieties
The Varieties Versus Locally Available Ones
Responses to Identified Needs or Opportunities
Planting Materials
Reduction of Risk through Increased Yield Stability and Less Variability across Locations and Seasons/Years
Information for Extension
Distribution to Provinces
Contact

Technology Release of Sweet Potato Varieties for the Lowlands
NARI officially released 79 first class lowland varieties of sweet potato held at Keravat during the research station's 75 th Anniversary celebration in May 2004. Details on the released materials are presented below.

Type of Release

The number of sweet potato varieties recommended for release is still high, thus require further narrowing. Obviously, a proper Genetic by Environment (G x E) trial under the main lowland agro-ecological zone would help. Another inexpensive way to evaluate their on-farm performances would be to monitor the release and feedback from farmers. This adaptive phase of research should take high priority and include very wet and mid altitude areas where information on the performance of these varieties is lacking. For the general lowland conditions however, the results of a Pacific Regional Agricultural Programme (PRAP) on sweet potato are adequate as the basis for making a ‘full technical release.'

Evaluation of Sweet Potato Varieties

The varieties were selected from a fairly rigorous and extensive varietal screening programme conducted under the European Union funded PRAP project between June 1990 and December 1998. Details of research done; the screening methods and selection criteria used as well as results and conclusions drawn are presented in a report titled ‘The Status of Sweet Potato Variety Evaluation in PNG and Recommendations for further Research', by Paul Van Wijmeersch, pp 674 – 682 of ACIAR Proceedings No. 99 titled ‘Food Security for Papua New Guinea 2000.'
The varieties were selected out of a total of 1, 167 varieties (254 from Laloki, 678 from Aiyura and 117 introduced from overseas) and evaluated at NARI Keravat for the lowland conditions. Evaluation was done over 9 years from which promising varieties were selected from five large screening, 16 replicated trials and 30 multiplication blocks. During the period, a wide range of climatic conditions (very wet to very dry) was experienced. Testing was also conducted at Laloki for the lowlands and Aiyura for the highlands.
Subsequent to the PRAP project, a sub-set comprising thirty-five varieties was selected for drought tolerant assessment at Laloki under the World Bank funded Drought Relief project. Selection of the sub-set was based on growth vigour assessments and lost plants during the severe El Nino drought in 1997-1998. Screening by the Drought Relief project resulted in selection and release of four lowlands drought tolerant varieties; K9, B11, Nuguria 5 and SI 278. More recently a thorough analysis of the original PRAP data on yield was done on the same varieties for yield stability resulting in the selection of 16 elite varieties for distribution under the World Vision Sweet Potato Food Distribution Programme for Bogia, Madang province (E. Guaf pers. com). The latest selections include: Kinabakab, Doy2, L949, L781, L949, L781, K9, Mas2, L46, K142, B11, L43, L942, KAV 61, RAB 36, SI 172, SI 85 and SI 108.

The Varieties Versus Locally Available Ones

While there is lack farmer field data to be able to make firm judgements on their performances against locally available varieties, the rigor and extent of research done on them however does provide us with reasonable confidence that the varieties are superior in a number of traits to local varieties. First and foremost, they have been selected because they have constant high to good yield with good market appeal and/or a preferred taste. For more details, see a report titled ‘Descriptive list of selected sweet potato varieties for lowland conditions as of December 1998' available from NARI. Several varieties have orange tuber flesh colour (a sign of a high B-carotene content) and high dry matter content (at least 30%) while four have been selected as drought tolerant.
The selected varieties have an acceptable level of resistance or vigorous growth making them tolerant to the scab disease. This is because they are mainly from the Pacific region, especially from Papua New Guinea (53) and Solomon Islands (18) where many resistant or tolerant varieties exist. They also consist of a number of deep-rooted varieties, which could be planted as control measures against sweet potato weevil and rat infestations. Flesh texture and taste after boiling vary from soft to firm and the taste from not-sweet to sweet.
Generally, as well as possessing good yields, the varieties offer a considerable range of options for a number of important traits like age to maturity. There are several early maturing varieties which could be planted to escape infestation from pest and disease or dry periods and variety of flesh colour, texture and taste for consumers and even the Fast Food Industry to choose from.

Responses to Identified Needs or Opportunities

By releasing the varieties, NARI is responding to the needs of subsistence farmers throughout the lowlands where sweet potato is the overall number one staple crop. On the national scale, the release would respond to the food requirement needs of 53% of the population or 2.1 million people (Allen, B; Bourke, R, M; Hanson, L; 200).
The good eating quality varieties should also serve the interest of the growing Fast Food Industry where take-away foods such as sweet potato scallops and chips (in place of English potato due to potato blight) are increasingly becoming popular among consumers. They will also be available to serve the dietary needs of Institutions that wish to engage in self-sufficiency food production projects and grow some of their own food.

Planting Materials

Planting materials for these varieties are readily available at Keravat. However, because of the observed yield decline due to infestation by pathogen and yield increases from cleaned or pathogen tested materials by PRAP, the materials including pathogen tested ones require renewing by growing out of pathogen tested tissue culture materials or cleaning field materials in the tissue culture laboratory. Some varieties have been observed to show less yield decline to viruses. The tissue culture laboratory at Keravat is currently maintaining an invitro collection of most varieties. There is plan to generate materials from this collection to establish in the field for distribution to farmers and to replace missing selections in the invitro collection with materials from field collections and overseas.

Reduction of Risk through Increased Yield Stability and Less Variability across Locations and Seasons/Years

There are good indications that the varieties can assist in the alleviation of risks associated with sweet potato production in the lowlands of PNG. The four drought tolerant varieties obviously satisfy this criterion. The recently selected 16 varieties for the World Vision Programme have stable yields and some have wide adaptability. Although no formal G X E trial was conducted, some of these varieties were found to perform well at Laloki and Bubia research stations and in other countries such as Tonga , Vanuatu and Sri Lanka . It was also observed during PRAP that varieties like K9, which performed well under wet conditions (Keravat), performed even better in places with a distinct dry season like Laloki. High priority should be given to testing of the varieties in very wet locations, e.g. Bali Vitu in West New Britain and Buin and Siwai in the North Solomons. Under PRAP, yield stability and wide adaptability were also illustrated by the fact that some of the varieties, which yielded well under PNG conditions, were originally from other Pacific and South East Asian countries.
Obviously one of the strategies to cope with risks in the farming systems is to release a number of superior varieties which are not just good in yield but those with a range of other desirable traits similar to multi-line releases from breeding programmes. The release of the varieties would be along the same strategy to cope with any risks in production and to meet any consumer demand.

Information for Extension

NARI has published a technical bulletin on the description of the selected sweet potato varieties for the lowland conditions, which is available for extension workers. The Food Crop section at Keravat is planning to produce a number of Toktoks or information leaflets, posters and radio programmes on the varieties to increase farmer awareness. Seven reports/papers were written on the sweet potato varieties and a number of them were presented in overseas conferences and workshops.

Distribution to Provinces

Many of the selected varieties were already distributed by PRAP to farmers and Division of Primary Industry Officers in the East New Britain province and to a number of other places in lowland PNG for distribution. These places include NARI's Bubia and Laloki research stations, the Vudal University, Cocoa Coconut Institute at Madang, and Fresh Produce Development Company for distribution to Karkar Island (Madang province), Manus, Buka, Kavieng and Nissan Island (North Solomon province).

Further releases are planed under the Keravat Outreach and Liaison programme and Agricultural Innovations Grant Facility (AGIF) projects. These should be properly coordinated so that the impact of the varieties is monitored in the farming systems.

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For further information, contact:
NARI Wet Lowlands Islands Programme
P.O Box 204, KOKOPO
East New Britian Province
Papua New Guinea
Phone: (675) 983 9145
Fax: (675) 983 9129
Email: nariirckerevat@nari.org.pg

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