Green yam sprouts are germinating from their beds of corn husks (Photo courtesy Dr. Balogun)
The production of yams, which are food security and poverty alleviation staples in West Africa, is constrained by scarcity of planting materials and low multiplication rates, which account for up to 63% of production cost. Tuber dormancy also hampers out-of-season production, while uncontrolled sprouting after dormancy causes storage losses. Microtubers produced in test tubes (in vitro) have been proposed as alternative propagules whose dormancy can be exogenously controlled (Balogun, 2005). Although the duration of dormancy of microtubers was shown to be affected by plant growth regulators applied at different growth phases, the tuber production rate remains slow, the low yields are not amenable to farm level production, and small tuber size limits direct transplanting to the field. Use of temporary immersion bioreactors in in vitro cultures has been recognized as a means to improve plant propagation in other crops, and the idea is adaptable to hundreds of species. Temporary immersion facilitates scale-up of propagation of large masses of plant tissue, which is useful because it does not require costly agar, reduces contamination in cultures, and provides a means for sequential manipulation of the nutrient medium at different developmental stages with minimal labor input.
The goal of this project is to identify optimum conditions for production of seed tubers of white yam whose dormancy can be efficiently controlled. This research will aid the optimization of protocols for seed yam production and increase seed supply and quantities consumed at lower expenditure levels. The immediate uses of the research results will be micropropagation of disease-free plantlets, in vitro conservation of plantlets without losses associated with field collections, and in vitro evaluation of yield in transgenic yam. The potential uses of the results include out-of-season production and extension of the storage cycle. The overall development impact is that enhanced yam productivity will help Nigeria to feed her people while also empowering them through trade.
Summary of Recent Activities
Dr. Balogun has recruited an MSc and a PhD student to work on the project, with both receiving fellowship support from the PEER grant. In October 2013, the team began a process of vine rooting as an alternative way of generating vines for the yam plants that will be used in the bioreactors. The master’s student participated in a field trip that exposed her to the process of plant tissue culture using bioreactors in November 2013. Tubers from a previous season’s planting were harvested in December 2013, and additional seed tubers were purchased from the local market. The seed tubers were directly planted while the remaining seeds will be pre-sprouted in a bed of carbonized rice husks. As instability of the local electricity supply has hindered past research efforts. Dr. Balogun has also ordered the necessary equipment to upgrade the solar power backup facility at her tissue culture lab.
In the first quarter of 2014, four extension agents will be invited to visit experimental fields and laboratories with the goal of project familiarization. In the field, data gathering on length of the dormant and non-dormant phases of each farmer-preferred genotype will be continued. Vines will be used to establish in vitro yam plantlets, followed by multiplication and bulking until a June visit by the PI to the U.S. partner at Penn State University to introduce the yam products into bioreactors. While in the United States, Dr. Balogun will also purchase bioreactor units and carbon dioxide reservoirs for installation at the University of Ibadan in the fall.
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