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Sweetpotato cultivars with improved storage root quality
Validated RNRRS Output. Home List by Audience List by Topic

Consumers and farmers in Africa will soon be able to benefit from the huge untapped potential of sweet potato thanks to a series of new findings. They include improved selection methods, guidelines for consumer tests, new breeding strategies, and knowledge of the factors that cause damage during handling and storage, among others. Sweet potato is considered the most under-exploited of the developing world’s major crops. The new knowledge can be used in programmes across Africa to ensure that this crop will fulfil its promise in fighting hunger, contributing to livelihoods and combating vitamin A deficiencies among the poorest of the poor.

Project Ref: CPH34:
Topic: 1. Improving Farmers Livelihoods: Better Crops, Systems & Pest Management
Lead Organisation: Natural Resources Institute (NRI), UK 
Source: Crop Post Harvest Programme


Contents: Description
Validation
Current Situation
Environmental Impact

Description

Research Programmes:

Crop Post-harvest Programme

Relevant Research Projects:  

R6507: The extension of storage life and improvement of quality in fresh sweetpotato through selection of appropriate cultivars and handling conditions. 1996 – 2000

R7520: Sweetpotato cultivars with improved keeping qualities for East Africa.  1999 – 2002

R6769: Investigating the potential of cultivar differences in susceptibility to sweetpotato weevil as a means of control. 1997 – 1999

Lead Institution: Natural Resources Institute, the University of Greenwich, UK
Contact person: D. Rees, E:mail: mailto:D.Reees@gre.ac.uk, Tel +44 1634 883522
Partners:

  • Natural Resources Institute, University of Greenwich, UK. D. Rees, K.I. Tomlins, Q.E.A. van Oirschot, T. Stathers, C. Moss
  • School of Science, University of Greenwich, UK. P. Harvey    
  • International Potato Center, Regional Office, Kampala, Uganda. R.E. Kapinga, N. Smit 
  • International Potato Center, Regional Office, Nairobi, Kenya. S. Agili, D. Maina, T. Mcharo
  • LZARDI-Ukiriguru, Mwanza, Tanzania. R. Amour, S.C. Jeremiah T. Ndengello E.J. Rwiza
  • Sugarcane Research Institute (Kibaha) Tanzania. M. Muhanna, K. Mtunda, M. Kilima, H. Kiozya
  • HortiTengeru, Arusha, Tanzania. T.Ndondi, M. Chottah
  • ARTI Uyole, Mbeya, Tanzania. C.M. Mayona, D. Mende
  • Dakawa ARC, Morogoro, Tanzania. D.N.V. Chilosa, A. Goa, A. Lipande, M. Kiteleki
  • Sokoine University of Agriculture, Morogoro, Tanzania. L.B. Mbilinyi
  • Namulongwe Agriculture Research Organisation, Uganda. B Odongo
  • Serere Agricultural and Animal Production Research Institute (SAARI), Uganda. S. Kabi
  • Silsoe College, Cranfield University, UK. J. Aked                                   
  • U.S. Vegetable Laboratory, USDA-ARS, South Carolina, USA. J. Bohac                                 


Research Outputs, Problems and Solutions:

Sweetpotato (Ipomoea batatas) is considered the most under-exploited of the developing world’s major crops.  Breeding initiatives for sweetpotato are at an early stage compared to other staple crops.  Given the enormous genetic diversity of sweetpotato worldwide, and that breeding programmes of sweetpotato are relatively new, crop improvements are expected to be rapid.  This cluster of outputs arises from projects undertaken to examine germplasm available in East Africa, the potential for breeding for specific  post-harvest/quality traits, and to identify strategies to facilitate effective cultivar selection.

Many of the project activities were focused towards understanding the physiological basis for differences among germplasm.  The resulting outputs of this cluster can feed into breeding strategies at two levels.  On the one hand elucidation of the basis of cultivar differences at a physiological and molecular level allows development of hi-tech selection strategies such as the use of molecular markers.  Such techniques are appropriate for international breeding programmes such as that at CIP, but are largely beyond the scope of the RIU programme.  On the other hand, the projects also resulted in identification of selection techniques suitable for National Programmes with more limited facilities.

Specifically, the most relevant outputs are:

  1. Identification of farmer, trader and consumer criteria for sweetpotato cultivars in east Africa and strategies to incorporate them into selection protocols during breeding.
  2. Methods developed for the use of consumer tests and trained taste panels to assess sensory characteristics of sweetpotatoes
  3. Breeding strategies to select for extension of shelf-life. Sweetpotato cultivars in East Africa have a wide range of shelf-life.  We established that a key factor affecting shelf-life is the efficiency by which storage roots heal wounds at low humidity.  Unfortunately high wound-healing efficiency is associated with lower dry matter content, although we do not know if this is a causative relationship.  Simple strategies, appropriate for use by national programmes, to assess wound-healing efficiency using tissue staining methods, or weight loss measurements have been developed.
  4. Increased understanding of the effect of root shape on susceptibility to damage during handling.
  5. Increased understanding of the cultivar characteristics affecting long-term storability.
  6. Strategies to select for cultivars with canopy and rooting structures that confer reduced susceptibility to field infestation by insects, especially Cylas spp.  This includes methods to assess appropriate root structures, and design of field trials with appropriate levels of insect pressure for most efficient cultivar selection.


Types of Research Output:

Product Technology Service Process or Methodology Policy Other
X


Major Commodities Involved:

The main commodity focus is sweetpotato.

Some of the principles established such strategies to incorporate farmer/trader/consumer criteria into the selection process and the relationship between shelf-life and wound-healing efficiency, might be applicable to other root crops.


Production Systems:

Semi-Arid High potential Hillsides Forest-Agriculture Peri-urban Land water Tropical moist forest Cross-cutting
X X X X X


Farming Systems: 

Smallholder rainfed humid Irrigated Wetland rice based Smallholder rainfed highland Smallholder rainfed dry/cold Dualistic Coastal artisanal fishing
X X X


Potential for Added Value:

The outputs described here should be combined with research outputs produced by the International Potato Center relating to sweetpotato improvement as well as those of:

  • “Superior sweet potato cultivars identified through a decentralised farmer-participatory approach” R5878, R6617, R7492, R8040, R8041, R8167, R8243, R8457 Richard Gibson.

Validation

How the outputs were validated:

Criteria (production and post-harvest) by which farmers (primarily women) select sweetpotato varieties were established by surveys conducted between 1990 and 1995 in all the zones of Tanzania where sweetpotato production is significant (Lake, Western, Eastern, Southern Highlands, Southern).  The accuracy of the criteria identified was confirmed by reference to the characteristics of the most popular varieties grown by farmers at that time.  The breeding programme within Tanzania has found that the best way to incorporate farmer criteria in the selection of new cultivars is firstly, to use farmer groups to assess early trials on-station, and secondly, to carry out on-farm trials of the more advanced cultivars.  This is a procedure that has been used successfully in Tanzania and throughout East Africa since the start of the work described here.  The fact that it is part of the strategy that has been used to release several successful new cultivars in East Africa, especially orange fleshed varieties through the VITAA programme, is firm validation of the strategy.Trader and consumer criteria were initially established by surveys in Mwanza, Meatu and Ukerewe Districts of Tanzania between 1995 and 1997.  Compared to farmer testing, it is less easy to test these criteria directly with traders and consumers, until a late stage of cultivar selection.  True validation of these findings would be through release and successful uptake of cultivars by all the end users.  As for the farmer criteria, the trader/consumer criteria and consumer testing have been part of the strategy that has been used to release several new varieties in East Africa.  The consumer testing techniques developed by this cluster have subsequently been used to assess cultivars during work in the VITAA initiative, coordinated by CIP. 

The work on farmer/trader/consumer criteria has also been subjected to peer review when published in scientific journals and presented at international conferences, such as the International Society of Tropical Root Crops, Arusha 2003.

The observations relating to wound-healing efficiency, its key role in controlling shelf-life and its tendency to relate to low dry matter content have been confirmed through work conducted by UK and Tanzanian researchers on several different groups of cultivars with different regional origins.  Thus genetic susceptibility to water loss was identified as the main driving force for root deterioration in trials conducted in 1997 and 1998 across 5 contrasting sites of Tanzania (Ukiriguru, Kibaha, Chollima-Dakawa, Uyole and Hort-Tengeru).  The control of water loss by wound-healing efficiency, and its relationship with dry matter content was confirmed through trials on three separate sets of germplasm (East African, North American and a range of international cultivars supplied by CIP) conducted between 1999 and 2002. The scientific arguments relating to root susceptibility to damage and wound-healing efficiency have also been validated through peer reviewed scientific papers in international journals. 

Relationships between canopy structure/root form and susceptibility to weevil infestation were derived during trials conducted by NRI and Ugandan Scientists in on-station trials in Uganda and Tanzania.  Despite the importance of these findings, additional validation has not been undertaken.

Where the Outputs were Validated:            

The criteria by which farmers (primarily women) select sweetpotato varieties were initially established by survey work conducted between 1990 and 1995 in all the zones of Tanzania where sweetpotato is a significant crop (Lake, Western, Eastern, Southern Highlands and Southern). 

Trader and consumer criteria were initially established by surveys in Mwanza, Meatu and Ukerewe Districts of Tanzania between 1995 and 1997. 

Further validation of the farmer/trader/consumer criteria and the consumer testing techniques developed during these projects have subsequently been used during work of the VITAA initiative in Uganda, Kenya and Tanzania. 

The observations relating to wound healing efficiency, its key role in controlling shelf-life and its tendency to relate to dry matter content have been confirmed through work on several different groups of cultivars with different regional origins.  Thus genetic susceptibility to water loss was identified as the main driving force for root deterioration in trials conducted in 1997 and 1998 across 5 contrasting sites of Tanzania (Ukiriguru, Kibaha, Chollima-Dakawa, Horti-Tengeru, Uyole).  The control of water loss by wound-healing efficiency, and its relationship with dry matter content was confirmed through trials on three separate sets of germplasm (East African, North American and a range of international cultivars supplied by CIP) conducted between 1999 and 2002.

The production systems where the outputs were validated were “forest-agriculture”and “high potential” (“semi-arid” for the work on susceptibility to sweetpotato weevil).

The agricultural system where the outputs were validated was “smallholder rainfed humid”


Current Situation

Who are the Users?

The outputs of this project cluster are being used by sweetpotato breeders and agricultural researchers during selection programmes for sweetpotato cultivars conducted by national agricultural programmes across East Africa, by CIP and also within the VITAA programme (coordinated by CIP) in Uganda, Kenya and Tanzania.

The outputs have also been disseminated widely across Africa, through distribution of the book “Sweetpotato post-harvest assessment: experiences from East Africa.”  And through the coordinating activities of CIP and the  Potato and Sweetpotato Improvement Network in Eastern and Central Africa (PRAPACE).  It is therefore likely that the information is being used to assist other breeding programmes across Africa, but it is difficult to assess to what extent this is happening.

Where the outputs have been used:

As described in (12), confirmed use of the outputs is localised to Tanzania, Uganda and Kenya.  The outputs have been disseminated widely across other parts of Africa, but it is difficult to assess to what extent.

The production systems where the outputs are currently being used are “forest-agriculture”and “high potential”

The agricultural system where the outputs are currently being used is “smallholder rainfed humid”

Scale of Current Use:

With no mechanism of continual assessment in place, it is difficult to be sure of the scale of uptake/use of the outputs.  So far the outputs are being used primarily wherever there is sweetpotato cultivar selection in East Africa.  Given that this cluster involved a number of breeder, that communication among sweetpotato breeders is good (often mediated by CIP, PRAPACE and by the DFID CPHP East Africa office) usage was established rapidly.  Firm evidence that usage is spreading outside East Africa is not extensive. 

Policy and Institutional Structures, and Key Components for Success:

The outputs described in this cluster are primarily for use by sweetpotato breeding programmes (national and international) and by programmes involved in selection of existing cultivars for dissemination.  For successful promotion and adoption of new ideas, good networking among extensionists and agricultural scientists, both within the national agricultural programmes and from the higher education sector is essential.  As local funds are often very scarce, the existence of networking organisations, with funding to organise regional meetings and exchange visits is very important.  Generally over the past decade, such networking has been successful.  A very important role has been played by network organisations such as PRAPACE (Potato and sweetpotato improvement network in Eastern and Central Africa) and SARRNET (Southern Africa Root Crops Research Network).   CIP interacts strongly with the national programmes, playing a vital role in the promotion of international interactions, and knowledge transfer.  Fora such as the 13th International Conference for the ISTRC held in Arusha also provide an opportunity for communication.  More recently, the East Africa office of the Crop Post-harvest Programme has also been very effective at promoting outputs of the CPHP.


Environmental Impact

Direct and Indirect Environmental Benefits:

The outputs of this project cluster will have a positive environmental impact through the promotion of sweetpotato production, and through reduction of post-harvest losses.  Sweetpotato is a crop that does not require high inputs, and is relatively drought tolerant, and so does not generally require irrigation. As it is relatively pest and disease resistant it is usually grown by small farmers with no chemical applications. It does not tend to lead to depletion of soil fertility.  With improved cultivars, production will increase while post-harvest losses will decrease.  Poorer sectors of the community will have a more secure food supply and will become capable of income generation, Thus there will be a decrease in the movement of populations into urban centres.

Adverse Environmental Impacts:

Very few adverse environmental impacts can be identified.  There is a possibility of an increase in the land area under cultivation, which could impact on conservation of wild areas.

Coping with the Effects of Climate Change, or Risk from Natural Disasters:

Yes.  As the crop is relatively tolerant to marginal agricultural conditions, it will help communities cope with greater climatic extremes. Food supply will increase resilience.  Increased income generation both through local and national markets will provide communities with capital which provides the necessary flexibility to increase resilience to natural disasters.


Relevant Research Projects, with links to the
Research for Development (R4D) web site
and Technical Reports:

R4D Project Title Technical Report
R5870 Uganda: Germplasm evaluation project
R6507 The extension of storage life and improvement of quality in fresh sweet potato through selection of appropriate cultivars and handling conditions.
R6617 Identification, characterisation and epidemiological significance of the whitefly-borne component of sweet potato virus disease in Africa.
Report Part 1. Part 2.
 part 1
R6769 Investigating the potential of cultivar differences in susceptibility to sweet potato weevil as a means of control  58 MB
R7492 Promotion of and technical support for methods of controlling whitefly-borne viruses in sweet potato in East Africa
R7520 Sweet potato cultivars with improved keeping qualities for East Africa
  • Sweetpotato Postharvest Assessment. Experiences from East Africa.
Contents Chapter 5
Chapter 1 Chapter 6
Chapter 2 Chapter 7
Chapter 3 Chapter 8
Chapter 4 Chapter 9
R8040 Rapid multiplication and distribution of sweet potato varieties with high yielding and B-carotene content
R8041 Sustainable Integrated Management of Whiteflies as Pests and Vectors of Plant Viruses in the Tropics: Phase 2 – Network Strengthening, Pest and Disease Dynamics and IPM Component Research.

Africa. Andes. Central America. Coordination.
Annex 1. Annex 2. Annex 3. Annex 4. Annex 5.
R8167 Promotion of sustainable sweet potato production and post-harvest management through farmer field schools in East Africa.
R8243 Working with farmers to control sweet potato virus disease in East Africa
R8457 Extending control of sweet potato diseases in East Africa