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Temporary Immersion Bioreactors (TIBs) to improve yam seed system

Temporary Immersion Bioreactors (TIBs) to improve yam seed system

30 September 2014

Traditionally, yam propagation is done by the field planting of whole tubers or large pieces (“setts”) of between 200 and 500g. Thus, farmers reserve a large number of otherwise consumable tubers-- which may still not be enough for planting every year. In the minisett technique, one tuber is cut into pieces called minisetts (each weighing 25-50 g) for planting. For instance, an average of 6 minisetts from 1 mother seed tuber will give 6 plants in the following year. In the vine rooting technique, stem cuttings from actively growing plants are rooted to generate new plants or tubers the following year (e.g., stem cuttings made from 6 plants obtained from 1 mother seed tuber which was cut into 6 minisetts will generate 180 new plants). These rates of propagation are still low (compared with 1:300 in some cereals), losses are encountered at rooting, and genotype variations exist.

As part of its objective to develop novel technologies for the high ratio propagation of high quality seed yam, the project Yam Improvement for Income and Food Security in West Africa (YIIFSWA) is developing protocols for producing seed yam using conventional tissue culture, aeroponics, and Temporary Immersion Bioreactor (TIB) technologies. The use of aeroponics - growing yam in soil-free, mist nutrient - has been demonstrated to be capable of producing 540 new plants from 1 tuber in 1 year. In addressing the problem of seed quality, the culture of single nodes of disease-tested plants in test tubes (conventional tissue culture) has been demonstrated to be capable of producing disease-free plantlets, with a multiplication ratio of about 1800 plants or tubers from 1 tuber in 1 year. However, this rate is still sub-optimal due to the limited size of the container (which puts a limit on the amount of air and nutrients), and the need for frequent sub-culturing which increases labor costs and the final cost of each plantlet.

Currently, the yam seed system is informal, and farmers reserve up to half of the year’s harvest for future planting, obtain seeds from fellow farmers, or purchase them from the market. In contrast, the formal seed system is about quality control and certification at all stages of the seed yam value chain, a gradual increase in the quantity of pre-basic to basic seeds and then of certified seeds that can be commercialized to farmers. The introduction of the formal seed system will require novel technologies, especially in terms of speed of production, uniformity, quality control, and certification of CLEAN pre-basic/basic and commercial seed yam in large quantities. Such rapidity is offered by the automation in the TIB technology.

Picture of TIB technology

 

Temporary Immersion Bioreactor technology is a propagation system that rapidly grows yam by intermittently immersing the plants in liquid nutrients in sterile laboratory containers. The system is propelled by air flow under pressure.

Picture of TIB technology

The TIB system is a new -generation tissue culture technology, involving timed immersion of plant tissues in a liquid medium to allow for the aeration of cultures. Each unit is a bioreactor - an enclosed sterile laboratory environment provided with inlets and outlets for air flow under pressure. This circumvents limitations associated with conventional tissue culture. In most crops tested (pineapple, cocoa, potato, etc), TIBs increased propagation rates. Our research is showing that it is possible to produce between 3600 and 7000 plants from 1 tuber in 1 year.

Picture of TIB technology

What is IITA doing on the bioreactor technology for yam?

In the framework of YIIFSWA, IITA is optimizing protocols for yam seed production in TIBs. IITA’s TIB setup is the Twin Flask, SETISTM type, having 1 container for the medium and the other for the plantlets. It was established with 128 units and, when running at full capacity, can produce up to 500,000 seed yam or plantlets per year. It is programmable and remotely controlled online.

Prior to YIIFSWA, most of the work on the application of TIBs in yam was on D. alata (water yam). At IITA, emphasis will be on D. rotundata (white yam) - the preferred species in the West African yam belt. Our research will explore the potentials for both plantlet and yam microtuber production in TIBs to facilitate the production of high quality pre-basic seed yam from which healthy basic and certified seed yam will be produced.

We are working on the science of optimizing the TIBs for yam seed production at IITA. Our team on Objective 5 of YIIFSWA is standardizing both TIBs and aeroponics for different genotypes in terms of nutrient composition, frequency of immersion in the nutrient solution, light requirement, genetic uniformity, plant density, acclimatization and post-laboratory survival of seedlings, etc. As we optimize these protocols, we will be providing technical backstopping to stakeholders (researchers from public and private laboratories, seed companies, and students) in the formal seed yam sector. Use of high quality seed yam by farmers will increase yield and profit margins and improve livelihoods. When the rate of propagation is increased, more yam and yam products will be available per year.