Yam production: technologies to the rescue

Yam is central to food consumption in West Africa. About 48 million tonnes of yam (95 per cent of global supply) are produced on four million hectares yearly in the sub region, mainly in five countries: Benin, Côte d’Ivoire, Ghana, Nigeria, and Togo, with Nigeria alone accounting for 70 per cent of its global supply.

Also, the changing consumption patterns overseas are opening up export opportunities. This is giving a new lease of life to yam farming. The expansion of earnings has drawn the attention of the Team Lead, Eupepsia Place Limited (Soilless Farm Lab), Samson Ogbole, who believes using  various  technologies  such as  vines or minisetts is key to supporting  more Nigerians to explore yam export opportunities  apart from the initiation of dialogue between producers and importers over the market requirements, quality standards and production requirements (good agricultural practices).

At International Institute of Tropical Agriculture (IITA), Ibadan, Oyo State, where Ogbole once pitched tent, farmers are being taught how they could plant any part of yam, instead of only the head.

Yam seed multiplication through aeroponics, others


In 2015, researchers at IITA grew various seed yams in the air by using the Aeroponics System (AS), raising hopes for the propagation of  disease-free planting materials.

In the preliminary trials, Dr Norbert Maroya, Project Manager for YIIFSWA project at IITA,  with a team of scientists, propagated yam by planting vine cuttings in AS boxes to produce mini-tubers in the air.

The AS is the process of growing plants in air or mist environment without the use of soil or an aggregate medium.Though technology is used by commercial potato seed producers in eastern Africa (Kenya, Uganda, Tanzania etc.), and southern Africa (Mozambique, Malawi, etc.),  growing yam on AS is a novelty for multiplying the much-needed clean seed yam tubers in large quantities.

“With this approach, we are optimistic that farmers will begin to have clean seed yams for better harvest,” Maroya said.

Preliminary results have showed that vine rooting in AS had at least 95 per cent success rate compared to vine rooting in carbonised rice husk with a maximum rate of 70 per cent. Rooting time was much shorter in aeroponics.

Maroya and Dr Robert Asiedu, the IITA Director for Western Africa, said AS came at the appropriate time for African farmers, because seed yam production was expensive and inefficient.

Farmers keep about 30 per cent of their harvest for planting in the following season, implying that they have less money or food.

Moreover, these saved seeds are often infested with pathogens that reduce farmers’ yield yearly.

However, with AS, yam producers can access clean seed yams.

The system increases the productivity of seed and ware yam and reduces diseases and pest incidence and severity (no soil-borne or vector-transmitted pests and diseases during the vegetative phase), he said.

“Yam is an important crop in Africa and addressing the seeds’constraint will go a long way in improving the livelihoods of farmers who depend on the crop for their livelihood,” he added.

In conducting the aeroponics trial, a special structure was built in a screen house with Dixon shelf frames using perforated Styrofoam boxes, as support for plant vines, while the developing roots of the plants in the air were enclosed in conditions of total darkness to simulate the situation of soil to the roots. For the plant and tuber to develop, an automated power house system was established for atomising periodically nutrient enriched water solution in the form of mist to feed the plants. The water solution includes soluble fertiliser, among other nutrients and the yam is fed at 15-minute intervals.

According to the scientists, the aim is to mass-produce the technology through private seed firms which have structures for propagation and multiplication of crop seeds and seedlings to reach many farmers.

The largest tuber in the first harvest from the AS experiment boxes was 9.6 grams, while in the second harvest, 32.8-gram and 110-gram tubers, and according to the scientists, the tubers could be planted in the soil, with expected high-yield.

Apart from AS, tissue culture and mini-sets are also seedling multiplication technologies for disease-free yam seeds.

Tissue culture is the artificial growth of plant cells from purified samples. In yam, cells are obtained either from leaves, vines or tubers and rapidly multiplied in a fully equipped laboratory. This is capable of producing millions of seedlings in weeks, and farmers can trans-plant such into fields after conditioning of such planting materials for some weeks, depending on the crop.

IITA, the National Centre for Genetic Resources and Biotechnology (NACGRAB), Moor Plantation, Ibadan, and National Agricultural Seeds Council (NASC) have tissue culture laboratories. These could be explored for cleaner yam seeds for higher production.

Yam seed propagation using the mini-sett technique involves selecting a disease-free yam variety after dormancy period (about four months after harvest) and slicing such into smaller pieces, with each having skin. Each set should weigh about 100 grammes, and dipped into fungicides, air-dry for two hours and set in carefully prepared beds under a shade.

These should be watered regularly and transplanted into fields one month after sprouting. So, timing of transplanting should coincide with established rainfalls or irrigation facilities should be available.

About 500 mini-setts could be produced from a medium-sized tuber, and this reduces disease infestation, food loss and increases productivity of farmers because they do not need to keep a large portion of their produce as planting materials amid hunger and poverty.


Yam vine cuttings


IITA initiated the AS, as one of the high ratio propagation technologies for seed yam tuber production. After nearly three years of experimentation, it was discovered that the AS could generate three types of planting materials for seed yam propagation. These are the mini-yam tubers harvested in AS boxes, the aerial tubers known as bulbils in water and white yam varieties, and vine cuttings.

On the average three tubers are harvested per plant on AS every four months. The water yam varieties were more prolific (up to 150 per plant) than the white yam (30 per plant for some varieties) in bulbil production.

Yam plantlets at the aeroponics screen house are growing at an exponential rate after being exposed to sunlight. Also, vines pruned from the aeroponics system and planted into soil are producing shoots within two weeks.

Maroya said the YIIFSWA project is planting over 1,800 one-node vine cuttings (in soil) from vines produced in the system to produce mini-seed yam tubers. He was excited that the shoots at the screen house were developing within two weeks of planting.

“To understand why this is significant,” he added, “it is important to note that vine cuttings pruned from plants grown on the field take about two months to establish roots and shoots. But given the vitality of these vines, roots and shoots develop within three weeks after being planted in the soil.”

The vine-cutting technology was developed to improve the multiplication rate of yam as well as reduce the impact of pests and diseases on seed tubers. The use of vine cuttings as a planting material gives a higher multiplication rate that is about 30 times more than in the traditional system.”

He said the AS and vine-cutting technology offer a rapid solution for high-output production of seed yam. They can address the need for the quick distribution of planting materials of improved varieties to large numbers of farmers.

With such results, YIIFSWA is set to achieve its goal of producing 100,000 clean planting materials by the end of the fourth project year. These will be distributed to national agricultural research and extension systems, seed firms, and farmers involved in producing certified or quality declared seed yam.


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