Scientifically known as Pachyrhizus Spp, the Yam bean is a nutrient rich legume root crop of the American origin closely related to the soya bean. It bears beans on top and tubers underground. It is propagated by true seed, has high nitrogen fixing capacity and large storage root yields .
Left : The yam bean tuber, Right: The yam bean plantlet
The tuber has properties like sweet potatoes or common yams and cassava. It can be made into flour and mixed with millet and other flours but it can also be taken as cooked fresh tubers or chopped it into pieces taken raw as salads and that is what is being promoted in Kampala as an urban salad.
Researchers are optimistic that the yam bean will contribute significantly to food security because unlike other root tubers, it is rich in protein, carbohydrates, zinc and iron which are nutritionally recommended plus other nutrients on top of improving soil fertility.
In January, 2009 scientists in plant breeding, agronomy and plant genetic resources from Makerere University College of Agricultural and Environmental Sciences (CAES) in collaboration with the International Potato Center (CIP) - an international research institute for tropical agriculture based in South America and research institutes in DR Congo , Rwanda and Burundi embarked on a project to popularising the use of yam beans as human food in Eastern and Western Africa.
The yam bean growing in a garden
The four year project funded by the Belgium Technical Cooperation titled, “Enhancing the nutrient rich yam bean (Pachyrhizus spp) to improve food quality, availability and sustainability of farming systems in Central and West Africa”is aimed at the availability of larger seed quantities for three to four varieties with high yields and adaptation to central African conditions.
Scientists describe the yam bean as an adventure and a challenge because the true seeds of the crop are inedible due to its high rotenone contents. Plant breeder from the Department of Agricultural Production Makerere University, Dr. Phinehas Tukamuhabwa said research in the laboratory and in the farmers fields for screening to determine rotenone in the yam bean have been developed with promising results.
“We are doing research on how this rotenone can be removed or deactivated from the seeds because once that is done, we are capable of recommending the bean for human and livestock consumption. We are doing this in collaboration with a University in Belgium” Said Dr. Tukamuhabwa.
Laboratory and Farmer fields experiments are being conducted in Luwero, Soroti, Namulonge , Kabale- Kachekano and Kabanyolo nearing commercialisation.
Achievements so far include the inclusion of 31 new accessions to the CIP gene bank, about 60 farmer varieties now maintained at CIP, and well adaptability in central Africa high lands conditions of Rwanda, Burundi, DR Congo where temperatures do not fall below zero and in tall grass savannah agro ecological zone.
“We hope by the end of the third year of this project we should be able to tell you which variety is the best but we can say right that there are prospects that farmers will take it as a serious crop and that some of these varieties are adoptable to our conditions “. Dr. Tukamuhabwa said.
He also explained that over 60 varieties of the yam bean were obtained from Peru and are differentiated by seed colours for example white, red, black while some varieties have soft and hard tubers which are taken to farmers for selection.
“What we are doing is adopting a technology by getting varieties got from Peru and, growing them in our own environment to see if they are doing very well and grow them with farmers. We bring different varieties, multiply them and do different experiments with them in different fields. Then when we harvest we get root tubers and develop them into different food types using our graduate student and also get the seed and see how much rotenone is there”
Some of the products from the yam bean
Two PhD, seven Masters and three under graduate students are doing different disciplines in regard to improving the yam bean. Of the two students from Food science and technology, one of them is looking at the rotenone problem and another one focusing on developing new products from yam beans.
He said unlike the common root tubers like cassava and sweet potatoes, the Yam bean yields very well over 30 tonnes per hectare and even higher if flowers are removed and where one wants both seeds and tubers , still the yields are comparatively higher than harvests from cassava, sweet potatoes and yams..
The break through in the reduction of the poisonous substance in the yam bean will be one of the most celebrated achievements in farming systems in Africa that will enhance food security for the hungry world.
‘We are also popularising the yam bean to make it acceptable to the population because changing peoples eating habits is another challenge. In Africa the yam bean is grown in Benin where it has been introduced with a lot of work done nearing adoption and now we are looking at Uganda, DR Congo Burundi and Rwanda”. Dr. Tukamuhabwa explained.
He added that although the yam bean roots are good and people like eating them , farmers are saying that the tuber is succulent and they want it to be hard with properties like sweet potatoes or common yams and cassava compelling researchers to develop roots which have more dry content so that farmers may feel more comfortable.
There is uncertainty of the continuation of this work after the third year of funding by the Belgium Technical cooperation is over, remains another big challenge.