Improving the Size and Market Value of an Underutilised Yam (Dioscorea esculenta) in Ghana:...

July 2013, Vol. 7, No. 7, pp. 732-741 Journal of Life Sciences, ISSN 1934-7391, USA

Improving the Size and Market Value of an Underutilised

Yam (Dioscorea esculenta) in Ghana: Implications for

Crop Breeding and Production Choices

Kwamina Banson1 and Kenneth Danso2

1. Agricultural Economics BNARI-Technology Transfer Centre (TTC), GAEC- BNARI, Box Lg80 Legon, Accra, Ghana

2. GAEC-BNARI, Box Lg80 Legon, Accra, Ghana

Received: July 19, 2012 / Accepted: January 24, 2013 / Published: July 30, 2013.

Abstract: Yam, Dioscorea esculenta which is a high value commodity is a threatened species in Ghana, due to several factors including neglect on the part of science, technology, research and development. Different doses of radiation were use to improve the size and market value of D. esculenta to promote it effective use and enhance effective conservation. We observed through repeated experiments that irradiation of yam planting material at 40 Gy gave the best results producing a M1 generation with a decreased number of tubers but with an increased tuber size per vine. Some yam characteristics are valued more than others, and prices vary across species, time, and market sites. Tuber weight exhibits an increasing marginal value and price per kilogram increases above an optimum size; therefore, yam producers and dealers derive additional reward from extra-large tubers. We conclude that, to effectively access and benefit from urban markets, producers should focus on the improved size and conical shaped-tubers, which are easy to process and meet the aesthetic qualities preferred by urban consumers. The implications for research on improved variety development to reduce poverty and for crop and resource management practices are drawn. Key words: Dioscorea esculentus, market, mutation, productivity, threatened species.

1. Introduction

Cultivation of indigenous agricultural varieties in

Ghana is characterized by low yield and productivity,

which are compounded in the long run by production

shocks due to environmental stresses such as drought,

pest and diseases. Coupled with international trade,

the demands for a particular variety of crop have

tended to favour only a few major crops which have

come to dominate agricultural production, processing

and commerce [1]. The demands for research and

hence funding have inevitably concentrated on these

same commodities. No attempt is made to improve

some of the traditional varieties. For example, most of

Ghana‘s indigenous vegetables and tubers have a

Corresponding author: Kwamina Banson, BSc, MSc, research

field: agricultural economics. E-mail: [email protected].

proven higher nutritive value than the exotic species.

However, since most of the indigenous varieties have

not been worked upon to improve yield potential,

palatability, flavour and general attractiveness, despite

their being highly nutritious they are still not widely

exploited commercially. As a result, not only are a

number of indigenous food species falling into disuse,

that can contribute fibre, medicine, fodder, etc but also

replaced by their exportable crops. However, these

neglected species are part of a rich economic, social

and cultural diversity, and many have the potential to

play a much more important role than they do today in

sustaining livelihoods and human wellbeing and in

enhancing ecosystem health and stability [2].

In spite of its huge economic potential and as a

source of food security, D. esculenta or Chinese yam

locally called “oboaduonum” or ‘broni bayere’still

DAVID PUBLISHING

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Improving the Size and Market Value of an Underutilised Yam (Dioscorea esculenta) in Ghana: Implications for Crop Breeding and Production Choices

733

remains an underutilized and under seriously genetic

extinction threat in Ghana. Lack of planting materials,

neglect by both farmers and researchers, and more

importantly, their displacement by improved varieties,

mining activities, bush fires, infrastructure

development and over-grazing coupled with small

tuber size has resulted in the almost complete

extinction of this yam species in Ghana. Consequently,

the full potential of this crop for income generation

through the domestic and international export trade

has not been realized due to neglect in production,

handling and trading systems as a result of it poor

sizes that inhibit its use for food and agriculture in

Ghana [2, 3]. Varieties cultivated for the Ghanaian

markets includes; ‘Pona’ and ‘Dabriko’ ‘Dente’,

‘Nkani’, ‘Afasie’, ‘kokoase bayere’, ‘Nkanfuo’

‘Ahabayere’, ‘Muchumudu’ ‘Afuun’, ‘Apoka’,

‘Asobayere’and ‘Ediamawoba’ with ‘Pona’ being the

most popular landrace cultivar of yams on the

Ghanaian market [4].

The expected role of mutation in a sustainable

agriculture is to contribute to the development of new

varieties presenting mainly resistance to diseases,

environmental stresses, contribution to recuperation

and protection of the environment, decreasing the

need for agricultural supplies and producing important

metabolites of fundamental importance in the human

diet [5]. Mutation research offers a wide range of

possibilities to crop improvement. In the short term its

most important contribution is the increase of the

quantity and quality of global food, feed and fiber

production. A complex list of desirable benefits

expected from mutation research and its productive

use is an important parameter that should be carefully

analyzed as research results come to light and

production reaches the market. Impact evaluation is

the intellectual tool that should respond to the need of

the situation.

Ghana is one of the developing countries that made

significant progress in biotechnology during recent

years. The Biotechnology and Nuclear Agricultural

Research Institute (BNARI) affiliated with the

Ministry of Agriculture, and Universities are

producing the most important and more productive

work in agricultural biotechnology research. This has

placed Ghana as one of the developing countries that

is doing significant progresses in biotechnology

among the scientific community in the world. The

research on biotechnology aiming the development

and adaptation of products and processes of interest

for the Ghanaian agriculture and agribusiness has

developed considerably in the last few decades. Over

two decades of application of induced mutation

techniques toward crop improvement in Ghana have

led to the production of improved mutant varieties

especially in two crops, cassava and cocoa.

Production constraints such as cassava mosaic

disease, cassava bacteria blight, arthropod pests, and

other biotic and abiotic stresses leading to small tuber

sizes, low productivity, rapid post-harvest

deterioration and inadequate starch and protein

content in the roots have been reduced to the barest

minimal with mutant varieties. Also production

constraints in cocoa during the 1980s as a result of the

Swollen shoot disease, virus which is transmitted by

mealy bug vectors and eventually destroys cocoa trees,

has been minimised with the mutant varieties.

Conventional breeding efforts attempting to address

many of the constraints to cassava and cocoa

productivity have had some success such as the TEK

BANKYE, a mutant variety of cassava with high dry

matter content (40%) and good poundability and

Cocoa Swollen Shoot Virus resistant mutant variety.

Therefore this research focused on the use of mutation

breeding to improve the tuber sizes of D. esculenta.

The purpose of this study was to improve the tuber

size and market value of D. esculenta using different

doses of gamma radiation to promote the effective use

of these species and enhance effective conservation

and sustainable use for food, agriculture and industry.

The Biotechnology and Nuclear Agriculture Research

Institute of the Ghana Atomic Energy Commission in


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collaboration with The Plant Genetic Resources

Research Institute (PGRRI) of the Crops Research

Institute of the Council for Scientific and Industrial

Research (CSIR) developed a breeding programme to

improve the size, weight and conical shape of the

underutilized yam “Dioscorea esculenta” The ultimate

aim of the breeding programme is to improve the

market demand and increase productivity and the

main focus is on meeting national food needs and

increased export opportunities.

In Ghana, tuber weight exhibits an increasing

marginal value and price per kilogram increases above

an optimum size; therefore, producers derive

additional reward from extra-large tubers.

The major objective of the study examined market

demand and productivity level in an underutilised

Yam (Dioscorea esculenta) in Ghana.

The specific objectives of this study were the

following:

� To identify barriers that prevents producers from

adopting the cultivation of D. esculenta;

� Improve tuber sizes using different doses of

radiation at 10, 20, 30, and 40 Gy;

� Analyse the market value of D. esculenta before

and after using different doses of gamma radiation to

improve it sizes.

It was hypothesized that aged farmers shun away

from the cultivation or adoption of oboedunum variety,

farmers turn to cultivate or adopt cultivation of

oboedunum variety as household size increases and

Price per tuber increase with increasing weight.

2. Methodology

The study started with a detail literature review on

theoretical approaches, on the concept of mutation

breeding, their adoption and impact on economic

development. Furthermore literature on the Ghanaian

yam market was analysed.

Both primary and secondary methods were used for

data collection from forty yam producers mainly from

the Northern and Eastern Region of Ghana to

determine their level of knowledge and awareness of

the underutilised yam, D. esculenta. 115 people were

interviewed in a market survey in the Greater Accra

Region, the centre of yam marketing. The field survey

(ex-ante and ex-post) took place from October 2009 to

January 2011 using standardized questionnaires. In

2009, the questioanire was designed to capture the

consumer and yam dealers level of knowledge and

awareness of the underutilised yam, D. esculenta.

Samples of indigenous underutilised Yam

(Dioscorea esculenta) were taken to all the yam

markets of Greater Accra region and yam producing

region to asked yam dealers, producers and experts

weather they have knowledge of the variety. Based on

the finding, experiment was design to improve the

variety using mutation. Radio-sensitivity analysis was

done to determine the LD50 of the seed yam and

based on the findings, dosage of 40, 30, 20, and 10 Gy

was emitted to the seed yam for the experiment. LD50

is the dose at which 50% of the seed yam to be

radiated will survive. The characteristic needed were

expressed in the subsequent generation of seed yams

from parent radiated yam harvested.

The survey districts were selected purposively in

the peri-urban areas of Greater Accra Region which is

a center for most yams produced in Ghana with largest

market segments. Communal leaders of farmer groups

and representatives of district governments were also

interviewed with unstructured questionnaires. This

helped gained insight into the policies that influence

the performance of the yam industry in Ghana.

Since the total number of yam producers and

exporters is not available for the design of a

probability sample, their selection was based on

snowball sampling in which interviewed farmers will

be requested to name other farmers.

In selecting the producers, care will be taken to

include farmers with different operational scales (i.e.

medium and large scale).

The surveys on market demand and productivity

assessment focus on “ex-ante” or “ex-post”


735

evaluations of the underutilized yam Dioscorea

esculenta. To improve the tuber size or weight (which

was 0.3 kg on the average before radiation) of

Dioscorea esculenta, repeated experiments with

different doses of radiation at 10, 20, 30, and 40 Gy

were used.

3. Results and Discussion

3.1 The Findings of the Farmer/Consumer Surveys on

Shortcomings with of D. esculenta

3.1.1 The Characteristics of the Yam Market

A survey conducted through the selected yam

markets revealed that most of them lack identifiable

physical infrastructures while majority of them

constitute a subset of a main market where other

commodities are at display.

Some of the sellers, especially new entrants mostly

display their yams on sacks and mats on the ground

at the mercy of the weather and without any well

defined mode of preservation and sometimes under

makeshift barns or shed but the well established

sellers have proper shed to store the yams as shown in

Figs. 1 and 2. Fried groundnuts are sometimes used by

some of the traders as baits to wade off mice and other

rodents that destroy the yams when they are in storage

at the market.

Female adults constitute about 90% of the sellers

with young males assuming the remaining 10%. Most

of the sellers do not possess any level of formal

education and are mainly from the Northern part of

the country where yam production is known to be the

highest. A good number of them also claim their

husbands/relatives are the producers and they do the

marketing thereby limiting the activities of middlemen

in the value chain.

Prospective yam buyers have the luxury of

bargaining for the price of a tuber until the sellers

settle on a bottom line for their produce. Hence yam

prices at these selected markets as prevailing in other

markets are determined as a result of the interplay of

demand and supply but with the sole aim of profit

Fig. 1 Yam storage, on pallets and covered with straw mat.

Fig. 2 Yams under shed.

maximization. The survey also showed that yam

farmers within the precincts of Accra visit such

markets to purchase yam setts (seeds) for cultivation.

The markets are seemed to be perfectly competitive

in nature and characterised by the free entry and exit

policy. However, even though entry and exit are not

restricted, new entrants need to pay a nominal fee for

registration with the market leaders (AMA, FAO,

1998) [6]. Since the product on sale (yams) is

homogeneous in nature the practice of ex hypothesi is

completely absent.

3.1.2 The Farmers

47% of the farmers interviewed were 30 years and

above. The minimum household number was 1 and

the maximum was 9 with 23% of interviewed farmers

having an average household size of 4. 46% of

interviewee had high school education while 20% of


736

farmers had basic school education (Table 1). Most of

the farmers (64%) interviewed had been farming for

more than 15 years. 53% of the farmers (below 30

years) who had been farming for less than 15 years

were aware of “oboaduonum” but had never seen it.

All farmers cultivated at least more than three species

of yam and the important amongst them are

‘Laribako’, ‘Muchumudu’, ‘Kulunku’ ‘Fuseini’ and

‘Nyumbo’ with ‘Pona’ being the most popular

landrace cultivar for both local and the international

market. The average farm size is 3.7 acres, minimum

is 1 and maximum is 5.

92% of the farmers interviewed were aware of D.

esculenta but 43% of them are cultivating it on less

than 2% of the total land area. Tuber weight exhibits a

diminishing marginal value and price per kilogram

decreases below an optimum size; therefore,

producers do not derive additional reward from

cultivating “oboaduonum” small tubers.

Table 2 indicated that as household size increases,

farmers turn to cultivate or adopt cultivation of

“oboaduonum” variety and other varieties to feed

family. It also shows that as farmers aged, they shun

away from the cultivation or adoption of D. esculenta,

although it is the aged group that knows the crop. Our

survey indicated that young yam farmers below the

age of 30 do not known the crop while those above

have cultivated the variety before. The result indicated

that awareness of “oboaduonum” existence among

farmers is directly correlated with experience of

farmers and farming years (Fig. 3). This observation

poses serious genetic erosion threat to the crop.

Stata outputs analysis of variance (anova) results

along with the regression results: Table 2. Top left is

anova table, and bottom is regression results. The

dependent variable here is cultivation of Oboeduenum

(oboedu), and the variable name is shown at the left top

of regression results table. The coefficients for age of

farmer, household size and availability of yam seed are

shown in the Coef. Column. Std. Err. is Standard Error,

t: t test statistics, P > |t|: the P values, and 95%

Confidence Interval. The results can be written in

Table 1 Demographics and farming statistics.

Variable Obs. Mean Std. Dev. Min. Max.

Age 40 2.75 0.438529 2 3

Hhsize 40 4.692308 2.214234 1 9

Edu 40 2.725 1.679247 1 6

Frmyrs 40 3 1.281025 1 8

Oboedu 40 0.45 0.5038315 0 1

Aware 40 0.975 0.2761921 0 2

Farmsize 40 3.7 1.697661 1 5

Seedavai 40 0.5 0.5063697 0 1

Table 2 Stata outputs analysis of variance (ANOVA) results along with the regression results. Top left is the ANOVA table and bottom regression results.

Source SS df MS Number of obs. = 40

Model 7.86605192 3 2.62201731 F (3.35) = 53.24

Residual 1.72369167 35 0.049248334 Prob > F = 0.0000

Total 9.58974359 38 0.252361673 R-squared = 0.8203

Adj R-squared = 0.8049

Root MSE = 0.22192

Oboedu Coef. Std. Err t P > ǀtǀ [95% Conf. interval]

Age -0.0661358 0.0919154 -0.72 0.477 -0.252734 0.1204623

Hhsize 0.0197063 0.0179957 1.10 0-281 -0.0168269 0.0562395

Seedavai 0.8902708 0.0765794 11.63 0.000 0.7348064 1.045735

_Cons 0.0911574 0.2303037 0.40 0.695 -0.3763841 0.5586988


737

Usage of D. esculentu When was the last time you used D. esculenta?

Fig. 3 Aging and awareness of “oboaduonum”.

regression equation form as:

Oboedu = 0.092 – 0.066age + 0.019hhsize +

0.891seedavai

An R Square of 0.82 means that differences in age,

household size and seed availability can explain 82%

of the variation in adoption rates of “oboaduonum”

(Table 2).

Farmers were asked if they would adopt the

cultivation of oboedunum if improved seed were made

available to them and the result (seedavai, b = 0.8903)

is statistically significant at least at 99% level (P =

0.000, it is less than 0.0005), and the coefficient is

positive which would indicate that if improve seeds are

made accessible to the farmers they would adopt the

cultivation of oboedunum variety -- which is what we

would expect (hypothesis).

Thus, to effectively enhance adoption of

“oboaduonum” variety, research focused on

improving variety to increase tuber size, low weight,

and it conical shaped-tubers, which are easy to process

and meet the aesthetic qualities preferred by urban

consumers. The implication for research to improve

variety development was to reduce poverty and

improve crop and resource management practices as

well as its nutritional content. The numerous tubers

produced by the plant already make it an ideal

candidate for adoption as shown in the Fig. 3.

3.1.3 The Consumers

Of the 115 consumers interviewed, showing them

sample of the indigenous or unimproved D. esculenta,

82% had not seen the variety before. Consumers were

asked how likely they would purchase this variety if

made available in the market and about 48% of them

indicated how unlikely to buy the variety (Fig. 4).

Some of the reasons attributed are that; the variety is

not available at the market, some said, it small sizes

will make it inconvenience to peel, others said due to

their large family size, it will require intensive work to

get it prepared for the table compared to large once.

They also said due to its small sizes, it will not store


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longer in storage (Table 4).

3.2 The Breeding Program Designed to Increase

Tuber Size and Weight

Experimental design consisting of 50 Samples each

of the indigenous variety of D. esculenta seeds were

exposed to gamma irradiation at a dose of 0Gy

(control), 10Gy, 20Gy, 30Gy and 40Gy at the

Biotechnology and Nuclear Agriculture Research

Institute. These radiated samples were planted in

Greater Accra Region, BNARI research fields, and

also at Bonsu in the Eastern region at the Plant

Genetic Resources Research Institute (PGRRI) of the

Crops Research Institute of the Council for Scientific

and Industrial Research (CSIR). These were harvested

after nine months. Tuber weight increased with

decreasing number of tubers per vine with increasing

irradiation dose compared to the control. Observation

through repeated experiments indicated that

irradiation of tubers at 40 Gy decreased the number

of tubers per vine and marginally increased the tuber

size at M1 generation suggesting a correlation

between tuber size and number of tubers per vine as

shown in Fig. 5.

3.3 Willingness to Pay for D. esculenta

According to the market respondents, after tasting

samples of the D. esculenta given to them, and also

according to sensory evaluation carried out by the

food science department of BNARI, have similar

properties as Pona which is the most preferred variety

of yam both at local and international market. Price

per kilogram is also relatively higher compared to all

the other yam varieties. The wholesale price of

Fig. 4 Chances of adoption of “oboaduonum”.

Table 3 Reasons for disliking this yam.

Frequency Percent Valid Percent Cumulative percent

Valid not available 8 17.4 17.4 17.4

Small size makes it inconvenient to peel 21 47.8 47.8 65.2

Demand more work with preparation due to its size 12 26.1 26.1 91.3

Poor storage 4 8.7 8.7 100.0

Total 45 100.0 100.0


739

Control (0Gy) 10Gy

20Gy 30Gy

40Gy

Fig. 5 D. esculenta tuber sizes at M1 generation.

Ghanaian yam has also been increasing as export

quantities increase.

Yam tuber weight exhibits a diminishing marginal

value and price per kilogram decreases below an

optimum size; therefore, producers do not derive

additional reward from cultivating “oboaduonum”

small tubers before the experiment. The size and

weight of the tubers increased to an average of 1 kg

against 0.3 kg/tubers of the control (unirradiated

planting material). The maximum and minimum

weights of the 40Gy tubers are 1.5 kg and 0.8

respectively. Tuber weight exhibited an increasing

marginal value and price per kilogram increased

above an optimum size; therefore, producers would


740

derive additional reward from extra-large tubers.

According to the market survey, retail prices of yam

have increased from GH¢ 0.20 per kg (2000) to GH¢

1.5 per kg (2012). Yam prices are highest in June and

July when the most preferred variety of yam, the Pona,

is out of season and in low supply. Farmers are able to

get a higher price for other varieties such as

‘Laribako’, ‘Muchumudu’, ‘Kulunku’ ‘Fuseini’ in

June and July relative to other points in the year.

Demand is particularly high for quality yam during

the summer months when production is low and

exports can command a higher market price. D.

esculenta is not exceptional since its texture and taste

is similar to the Pona type.

Both the farm gate and wholesale prices of

Ghanaian yam have been steadily increasing in recent

years, with wholesale prices increasing at a higher rate.

About 52% of consumers are likely or willing to buy

D. esculenta at the local market next to Pona (Fig. 4).

As consumers’ willingness to pay a higher price for D.

esculenta yam increases, farmers will increase their

production. Local farmers and exporters indicate a

strong willingness to purchase seed yam if it were

more readily available. Access to seed yam would

expedite cultivation of D. esculenta tubers to meet

rising demand.

Observation through repeated experiments indicated

that irradiation of tubers at 40 Gy decreased the

number of tubers per vine and marginally increased

the tuber size at M1 generation suggesting a

correlation between tuber size and number of tubers

per vine as shown in Fig. 5.

4. Conclusions

The results of market survey indicated that

“oboaduonum” is nearing extinction and farmers are

willing to cultivate it if the size is improved and

planting materials made available. The size and

weight of the tubers increased to an average of 1 kg at

40 Gy against 0.3 kg/tubers of the control

(unirradiated planting material). Tuber weight

increased with increasing irradiation dose. The tubers

of 10 Gy, 20 Gy, 30 Gy had an average weight of 0.54

kg, 0.68 kg, and 0.74 kg, respectively. Tuber weight

exhibited an increasing marginal value and price per

kilogram increased above an optimum size; therefore,

producers derive additional reward from extra-large

tubers. We conclude that, to effectively access and

benefit from urban markets, producers should focus

on the improved size and conical shaped-tubers, which

are easy to process, meet the aesthetic qualities

preferred by urban consumers and can also fetch more

money as a vine can give more yams compare to the

pona with just a yam per vine. This will improve

productivity and food security. This also provide

avenue for investors to invest in seed yam production

in Ghana because: there is increasing Demand for

Yam, Quality and preferred taste of Ghana yam,

Access to World Markets, Good roads, seaports and

airports, Support of Government, Trusted partners in

MiDA and ADRA, Low labor costs for farm

operations, Warm and friendly people, Politically

stable democratic government, Positive business

enabling environment, and more (MiDA, 2011) [7].

Acknowledgments

The corresponding author would like to take this

opportunity to express very sincere thanks and

appreciation to the manager of the Biotechnology

Center of Biotechnology and Nuclear Agriculture

Research Institute for inviting me to undertake this

work, for providing me with appropriate background

information and for taking the time to discuss his

views with me. I would also like to take this

opportunity to express sincere thanks to Prof.

Josephine Nketsia-Tabiri, director of the BNARI for

providing her comments and views. I would also like

to thank all those who contributed either through

responding to the questionnaire or who gave up their

time to discuss the issues with me directly. In the

latter category I am particularly grateful to Ebenezer

Kondo for his assistance, and my family especially my


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wife Irene Baaba Banson and all my children for their

support.

References

[1] D. Horna, M.R. Al-Hassan, S.W. Alhassan, O.K. Bonsu, J. Falck-Zepeda, G. Guillaume, et al., Assessing the Potential Economic Impact of genetically Modified Crops in Ghana: Tomato, Garden Egg, Cabbage and Cassava, PBS Report, October 2006, 2006.

[2] Li Longwe, Malawi country report to the FAO on plant genetic resource, (Leipzig, 1996), FAO, Compiled by: Malawi Governament, June, 1995.

[3] G. Hawtin, Underutilized Plant Species Research and Development Activities – Review of issues and options, A report submitted to the chairs of the GFU Steering

Committee and the ICUC Scientific Advisory Board, July, 2007.

[4] E. Otoo, R. Akromah, M. Kolesnikova-Allen, R. Asiedu, Ethno-botany and morphological characterisation of the yam pona complex in Ghana, 2009.

[5] M. Carneiro, Introducción y Panorama General, in: M. Carneiro, (Coord.) Estratégias de biotecnologia agropecuária para el Cono Sur. Montevideo, PROCISUR, 2000, pp. 1-8. (in Portuguese)

[6] AMA, FAO, Food Supply and Distribution To Accra And

Its Metropolis Workshop Proceedings, Accra, Ghana,

13th-16th April, 1998.

[7] Millennium Development Authority (MiDA), Yam Seed Production, Accessed on 23rd September 2011, http://www.mcc.gov/documents/investmentopps/bom-ghana-eng-yams.pdf.

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