Increasing farmers and breeders access to yam (Dioscorea spp) diversity: The case of Forest- Savannah Transition Agroecology

A study was conducted in five yam-growing communities in the Forest Transition Agroecological Zone of Ghana to identify cultivated yam varieties, their distribution and intensity of cultivation and to document the rate and causes of landrace germplasm loss. Generally, the cultivated varieties ranged from 9 to 16 with a mean of 12. The most diversity was found in Sankore (Asunafo South District), followed by Sampa in the Jaman North District, Asantekwa in the Kintampo District, Ejura in the Ejura-Sekyedumase and Mim in the Atebubu/Amantin Districts with 16, 15, 12, 11 and 9 cultivated varieties respectively. Dioscorea rotundata is most widely cultivated species of yam followed by Dioscorea alata, Dioscorea cayenensis, Dioscorea praehensilis and Dioscorea bulbifera respectively. Factors such as good culinary characteristics, high yield, seed generation capacity, good storage characteristics and resistance to biotic and abiotic stresses were important criteria for selection of variety. The market and utilization were major determinants of continual cultivation of a variety or its neglect.

Yam is a staple food crop of over 300 million people in tropics and subtropics (Mignouna et al., 2003).Ghana is one of the most important yam producing countries in the world; it is the third (9%) behind Nigeria (66%) and Cote d'Ivoire (13%) in terms of production (FAO, 2009).It is an elite crop, preferred over other root and tuber crops in West Africa and it is the food of choice at festive occasions, and the only crop that is celebrated wherever it is cultivated (Coursey, 1967;Hahn et al., 1987).Resource poor people, especially women, derive a good income from its production, processing, and marketing (Dufie, 2009).It also constitutes a cheap source of carbohydrate in the diets of millions of people worldwide and in tropical West Africa it provides some 18 metric tonnes of food for people in the yam zones.Yam also constitutes 53% of total root and tuber consumption in West Africa (Asiedu and Otoo, 2009).
Yam, therefore, is not only an important stable crop in West Africa but also an important cash crop.It contributes 12% of dietary energy supply and of the major agricultural food items in Ghana traded in 2010; yams were among the most important crops (top exports) with the net trade (export) of 7030 tonnes valued $4245000 (FAO, 2010).The importance of yams to the Ghanaian economy can therefore not be overemphasized.
Yam shows considerable diversity both at inter-and intraspecific levels (Okoli, 1991).The diversity under cultivation is further enhanced by the ongoing domestication of wild yam in various countries (Mignouna and Dansi, 2003;Scarcelli et al., 2006a).The diversity of yams in Ghana is poorly determined.Yam species generally, however, have adapted to different zones where they are often more abundant.D. rotundata, for instance, thrives well and is grown in the Guinea Savannah zone even though it can also be grown in the forest and Sudan Savannah zones.D. alata, D. cayenensis, D. dumentorum and Dioscorea praehensilis are mostly grown in the forest zone.In terms of utilization as food, D. rotundata is the most popular yam in Ghana followed by D. alata, D. cayenensis, D. dumetorom, D. esculenta and D. praehensilis.Yam (Dioscorea spp.) belongs to the genus Dioscorea, representing more than 600 species worldwide (Coursey, 1967).The Dioscoreales are believed to be amongst the earliest angiosperms that originated in Southeast Asia, but followed a divergent evolution in three continents separated by the formation of the Atlantic Ocean and desiccation of the Middle East (Hahn, 1995).As a result, the major food species occur in three isolated centers: West Africa, Southeast Asia and tropical America (Alexander and Coursey, 1969).
Ghana however, is the leading exporter of the crop.It contributes about 17% of agricultural gross domestic product (GDP) and also plays a key role in guaranteeing household food security (Kenyon and Fowler, 2000).The crop occupies 11.6% of the total cropped area of Ghana and annual production is estimated to be 5.8 million metric tonnes in 2009 (FAO, 2009).
There are numerous yam species in Ghana including the D. cayenensis and D. rotundata as well as some wild species such as D. praehensilis.The relative importance of these species has not been determined hence the extent of their usage is not known Otoo et al. 773 resulting in loss of some landraces over time.For vegetative propagated crop such as yam, and being indigenous to the sub-region such an approach will greatly enhance the improvement of the crop.Germplasm of vegetatively propagated species generally often contains accessions which, although morphologically similar have different genetic origins and vice versa (Lebot et al., 1998).The first step in this direction is knowing the status of the gene base of the crop in the country especially at the Forest Savannah Transition where it is mostly cultivated, documenting the rate of loss and initiating action to conserve relevant germplasm.
The aim of the study therefore was to identify the cultivated varieties of yam and their distribution in different zones in the Forest-Savannah Transition Agroecology in Ghana, the extent of landraces loss, causes and farmers' variety preference criteria.

Study area
The study was conducted in the forest-savannah transition zones in Ghana (Figure 1).Major yam growing communities were selected from each of the districts for the study.The study area covers all the tiers of yam production in the country.It included for instance, Mim in the Atebubu/Amantin District (average production per year of 250001-459860t), Asante Kwa in the Kintampo District, Sampa in the Jaman North District, Ejura in the Ejura-Sekyedumasi District (average production per year 100001-250000t) and Sankore in the Asunafu South District (average production per year 10001-25000t).Yam production is very important in these districts especially Ejura-Sekyedumasi, Kintampo and Atebubu/Amantin (Figure 1).The other districts were added in order to obtain as much biodiversity as possible.Selection of these districts was targeted at capturing as much diversity as possible.
To assess the diversity of yams at each location, a Participatory Rural Appraisal approach was used to obtain relevant information from the farmers.It also included focus group discussions and key informant interviews.
In each of the zones, a group of at least about 30 farmers were organized and taken through a discussion based on the checklist prepared (Appendix I).The information obtained was organized in a form that it could be well communicated.Gender and ethnic zones to effectively capture relevant data on parameters such as cooking quality and preferences disaggregated the participants.
The distribution and intensity of cultivation of cultivated varieties were documented.The rate of variety loss was assessed using 4×4 matrix system (Appendix II).
The study also carried out the following activities: an inventory of the cultivated varieties in the different yam production zones and assessment of their distribution and extent of cultivation; determination of the rate of landraces loss and its variation across villages; documentation of the reasons that underlie the landraces loss and its variation across diversity zones, identification of the different yam diversity zones in the country for development actions, identification and prioritization of the farmers' variety preference criteria across zones, and documentation of the cultivated varieties for the construction of national yam database.households and also in larger acreages; all other varieties are cultivated by few households and in small acreages.This trend was consistent for almost all locations.

Results
In the Ejura Sekyedumase district, however, D. alata cv Matches, and D. rotundata cvs Dente, Lilee and Ama Serwaa are all cultivated by many household on large acreages.Varieties such as Akaba, Nananto, Nentipo, Yesu mogya and Afebetua have the potential of disappearing.D. rotundata cvs Yesu mogya and Afebetua are almost at the brink of extinction.
In the Mim community in Atebubu District, D. rotundata cvs Pona, Serwaa and muchumudu are also in danger of extinction, due to the low number of households cultivating it and the small acreage of cultivation.D. alata cv Matches is cultivated by many households and in large acreages.
At Sampa in the Jaman North district, there is no one variety that is cultivated by many households and on large acreage.Most of the yams varieties cultivated in the area are by few households and on small acreages.All other varieties except D. rotundata cv Larebako are cultivated in small acreages.D. rotundata cvs Pona, Tila, Tempi, Teacher Takyi and Lobare are gradually getting extinct.Some farmers also indicated their preference to D. praehensilis.
Similarly at Sankore, all the varieties are cultivated in small acreages with an exception of D. cayenensis cv Afun; all others are cultivated by a few households.Although this is not a major yam producing area, there are several yam germplasms in this area.D. alata cv Apoka, and D. rotundata cvs Dente, Nnokoben and Pona were listed as varieties on the brink of extinction.
A wide diversity of D. rotundata yam species was documented in the study areas; 78% in Mim, 58% in Asantekwa, 60% in Sampa, 44% in Sankore and 82% in Ejura.D. alata varieties were 22% in Mim, 33% in Asantekwa, 33% in Sampa, 44% in Sankore, 18% in Ejura.Only one variety of D. cayenensis (D. cayenensis cv Afun) was found at Sampa and Sankore.It was only at Sankore that D. bulbifera cv was documented as a cultivated species.The maturity period also correlated positively to the harvesting type (r=1), with all D. rotundata varieties except for D. rotundata cvs Dente, Serwa and Tempi, being early maturing and thus double harvested.D. alata, D. cayenensis and D. bulbifera were late maturing and thus singly harvested.Income and food security were major determinants of distribution and intensity of cultivation of a particular variety across all locations, gender and ethnic groupings.
The Table 2 shows the rate of variety loss in the studied communities.Results from Table 2 show that the  x: indicates the level of importance, with x-least important and xxxxx-most important.
diversity is lower at Mim than the other locations.
Although the number of newly introduced varieties is more at Sampa than the other locations, the rate of variety loss is also greater than all the other locations.This means that yam cultivation is expanding in the area than the other locations hence new varieties are being explored and those not satisfactory enough are quickly lost.There were however, no newly introduced varieties at Asante Kwa in the Kintampo district.The rate of variety loss is therefore the least at Mim in the Atebubu District.
To ascertain the reasons for preference of one variety to the other, assessment was done on farmer preference criteria ranking them in the order of importance (Table 3).From Table 3 above, it can be seen that good productivity, high seed production capacity, good post harvest storage characteristic of the tuber, tolerance to high soil moisture and resistance to drought are the most important criteria farmers look out for in selecting yam varieties in the Ejura area.In the Kintampo area, however, good culinary characteristics, good productivity, low staking demand, good storage characteristic of the fresh tuber and resistance to pest and diseases are the most prominent criteria.There is not much difference between criteria for Atebubu, Sankore and Sampa.Among these three locations, resistance to drought, resistance to pest and diseases, tolerance to weed, high seed production capacity and good post harvest storage characteristic of the tuber dominated.
From Table 4, the importance of agro-morphological and environmental (biotic and abiotic) factors to the farmers was more than all the other factors.Agromorphological alone accounted for about 50% in terms of importance in about all locations except Kintampo where environmental factors dominated.Cultural factors however accounted for about 4.51% in the Kintampo district, 1.17 in the Ejura and 0.82% in the Atebubu districts.

DISCUSSION
Local yam classification systems exist in all yam-growing areas, and are often based on relevance or the characteristics of the individual yam variety.Previous studies revealed an intricate naming system where the most important or recognizable feature of the yam is used in naming it.These names are often descriptive.Farmers often preserve varieties they think is important and neglect unimportant varieties, leading to the loss of such varieties.The continuous existence of a particular variety, therefore, is an indication of its relevance in one way or the other to a particular individual or community.D. rotundata cv Pona, for instance, is an early maturing variety, and therefore amenable to double harvesting.Many households cultivate it albeit in small areas.This was attributed to the poor storability of this variety and the high cost of its seed yam.Even though it is the yam that attracts the premium price, its poor storability means that it is often depleted very quickly after harvesting.The seed yam is also often not available making it very expensive and increasingly putting it out of reach for the resource-poor farmer.
D. rotundata cvs Afebetua, Tela, Dobare, Fuseini and Dente are cultivated by few households on small acreages.This was attributed to the relative low market value of these varieties compared pona, for instance, thus placing these varieties in danger of extinction if no serious measures are taken to collect and conserve.
The high patronage of D. alata cv Matches and D. rotundata cv Mmonyiwa in these locations could be attributable to the good storability of these two varieties.Farmers therefore can rely on these varieties for both home consumption and marketing during the hunger period.The former variety for instance, is known to have being introduced to Ghana from Cote D'ivoire.Due to its high propensity to establish, it was distributed using matchbox as the standard multiplication size.This, coupled with its late maturity and ability to be used for several food forms has enhanced its spread in the country.
To enhance germplasm preservation therefore, local agro-biodiveristy, decentralized participatory breeding could be the preferred approach to breeding (Kirsten vom Brocke et al., 2010).
In choosing varieties, it was clear that agromorphological characteristics such as good culinary characteristics, good productivity, low staking demand, good storage characteristic of the fresh tuber and resistance to pest and diseases are the most prominent criteria.Hence any variety improvement programme that fails to take cognisance of these facts is bound to fail.It was therefore in agreement with Tamiru et al. (2007) assertion that often, overall structure of morphological diversity may be consistent with the local yam classification system.

Conclusions
A wide diversity of yams exists in the study area, however more and more of these diversity is getting extinct.There is the urgent need to collect and conserve these varieties.D. rotundata is most widely cultivated species of yam followed by D. alata, D. cayenensis and D. bulbifera respectively.Quadrant 4: Few households, small area (--)

APPENDIX
Varieties in quadrant 4 are those that are disappearing.Note however, that in this same quadrant are also found varieties that were newly introduced in the village.
Start filling this table (use Excel when back to office for your statistical analysis): DHV: Double harvest variety, SHV: single harvest variety, NIV: newly introduced variety, Q: quadrant.RVL = (Q4 -NIV)/Total number of varieties.

Reasons of variety loss
 Take one by one the varieties in quadrant 4 and ask farmer to give the reasons why they are being abandoned.Generally the reasons vary from variety to variety.

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Carry out individual survey with 20 farmers from the group.Let them tell you individually (isolate them) why, according to them, varieties are being disappeared.

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Carry out individual survey in each village.

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You can also use the matrices comparison method.
of the comparison of the distribution and intensity of cultivation are shown in Table 1.In the Mim community in Atebubu-Amantin District, D. alata cv Matches and D. rotundata cv Muchumudu are widely cultivated by many households and in large acreages.D. rotundata cvs Pona, and Serwaa are however in danger of extinction, due to the few number of households cultivating it and on the small acreage of cultivation.Similar trends were observed at Kintampo North District, where Dioscorea alata cv Matches and D. rotundata cv momnyowa are cultivated by many

Table 1 .
Distribution and intensity of yam varieties at various locations.
+: under household means lot of household, and under extent means cultivated in large acreages (greater than 2 acres), and -: under household is few household, and under extent is small acreages (less than 2 acres).

Table 2 .
Analysis of rate of yam variety loss at various locations.

Table 3 .
Preference criteria of farmers in the selected localities.

Table 4 .
Percentage importance of technological, agromorphological, environmental and cultural factors to yam production.

APPENDIX I: VARIETY DOCUMENTATION (GUIDE OF DISCUSSION)
Quality (taste, elasticity, expansion, presence of eventual lumps)  Quality of chips (taste, softness)  Quality of boiled yam (taste, softness, become hard when cool?)  Quality of the cossettes (flour, quality of the pate, etc.)