Scientists work to save the Irish potato in Kabale

By Christopher Bendana

The potato (Irish) that has fed the people of southwestern Uganda (Kabale) for generations is being threatened by several pests and diseases, including the potato bacterial wilt. These are affecting potato production as plants dry up or produce small tubers.

Abel Arinaitwe, a plant pathologist at Kachwekano Zonal Agricultural Research & Development Institute (KAZARDI) located 8km from Kabale town, says the potato bacterial wilt makes the plant sag. He discloses that this can be transmitted through infected seeds and soils, especially during the rainy season.

Arinaitwe says it can be managed by spraying with fungicides.

He adds that apart from the bacterial wilt, potatoes are also attacked by other diseases such as the late blight. This is a fungal disease that makes the leaves brighten with blotches, the stems turn brown and black and then the leaves collapse.

Arinaitwe discloses that late blight sometimes attacks the tubers, causing them to rot. This especially happens during the rainy season.

KAZARDI is one of the 14 institutes of the National Agricultural Research and Organisation (NARO) spread across the country. It spearheads research and development programmes aimed at increasing agricultural production in the southwestern highland agro-ecological zone.

Development of new breeds

Because the local breeds are susceptible to pests and diseases and crops lose their resistance over time, plant breeders are ever developing new varieties.

Arinaitwe says they import new varieties from South America, the epicentre of potatoes. The varieties are then cross-pollinated to get varieties that can adapt to conditions in Uganda. This process is what is termed as conventional. Sometimes, a system called tissue culture is used to multiply the new potato plants, which are then used to generate the seed potato.

Arinaitwe explains the process of cross-pollination as a controlled pollination between varieties a researcher is interested in. It is usually a cross between a variety which may be a landrace (local variety) with another variety which may be imported that has traits a plant breeder is interested in.

After pollination, the breeder collects the potato berries which are germinated in the soil to produce seedlings. These are evaluated for performance in the field and the best ones are selected to produce the seed potato.

Arinaitwe emphasises that each potato seedling produced from this type of pollination is unique. “Each seedling has a potential of becoming its own,” he points out.

The breeder, therefore, grows many and looks for the traits he is interested in.

For multiplication of plantlets using tissue culture (growing of plants in test tubes), Arinaitwe says they integrate these approaches though much emphasis is put on tissue culture because of its advantage.

With tissue culture, seedlings are produced at a faster pace in small space. Also, each plant can produce many plantlets. For example, one potato plant gives over 4,000 plants in three months.

According to Arinaitwe, there are several rooms at the main lab where tissue culture is carried out. The rooms are cleaned to be free of any micro-organism. There are machines that keep the plants at a required temperature for growth and machines that pump in air free of any micro-organism.

During the process, cleaning of specimens is done in a separate room, preparation for nutrients to form a medium to grow the plants is also done in another room, transfer of medium into test-tubes is also done in a separate room and there is a growth room at the other end. The medium is a plate where plantlets or cells are placed to germinate into seedlings in which nutrients are placed to support growth.

At Kachwekano, the researchers are making headway on developing varieties resistant to diseases, to the late bright. “We may release a variety that is late bright resistant next year,” Arinaitwe says.

Potato planting material (seed potato)

Potato planting material referred to as ‘clean seed’ are free of pests and diseases. Agriculturists say this is the first step in getting good yields. At KAZARDI, clean seeds are produced in partnership with an association of farmers called the Uganda National Seed Potato Producers Association (UNSPPA). Other farmers with interest in seed potato multiplication are being trained by KAZARDI, with sponsorship from ASERECA and other donors.

Production of quality/clean seed potato that is free of pests and diseases starts at KAZARDI. At the institute, small plantlets are grown in test tubes and later transplanted in clean soil in a screen house to produce small tubers called minitubers.

This technique has of recent been improved with the help of the International Potato Centre, which enabled KAZARDI to build a special screen house that allows the minitubers to be produced without soil. The plantlets from the lab are planted in raised and darkened boxes, whereby roots hang in the dark air space. Nutrients to support plant growth are supplied in form of liquid.

This is known as aeroponic production of clean seed potato, and it produces much more tubers from one plant compared to those grown in soil. It minimises soil-borne diseases and seed degeneration and, hence, increases seed and ware potato productivity.

Like other seed tubers, mini-tubers are allowed two to three months to sprout and then planted in a field at Kalengyere Station, which has suitable conditions for generation of pre-basic seed that is also planted in another season to produce foundation/basic seed.

It is the basic seed that is availed to UNSPPA or its equivalent farmers for growing it once more to produce commercial seed potato that is availed for ware potato farmers.

Potato varieties released from Kazardi

Over 10 potato varieties have been released. They include Victoria, Nakpot1, Nakpot2, Nakpot3, Nakpot4, Nakpot5, Kachpot 1 and Kachpot2 and Rutuku/Otankubuura. Each variety has its advantages and disadvantages.

Victoria is adaptable to both cold and warm areas and has a good texture when boiled or chipped.

Nakpot5 yields better in cool areas, has big oval tubers, yields high and makes good chips.

Kachpot1 has a relatively lower yield compared to Victoria but is the best for making crisps, while Kachpot2 is good for chips. These are the main varieties promoted by KAZARDI.

Farmers embracing new varieties

Juliet Akankwansa, a farmer at Kalandagasi in Kabale, is enthusiastic about the new varieties and agronomy training from KAZARDI. On her plot overlooking Lake Bunyonyi, she carries out potato seed spacing, application of fertilisers and harvesting. She is also aware that after some time, the potatoes lose their ability to resist pests and diseases. “After five cycles, they can also get infected by diseases and pests,” she notes.

For planting, Akankwansa buys a sack of potato seeds at sh100,000 from Kachwekano. She plants on a 100 by 100 foot garden. After a season, she harvests between seven and 10 sacks of seeds which she sells to farmers at 120,000 a sack.

Towards the harvesting time, Akankwansa cuts the outer part of the plant, leaving only the seeds (tubers) in the soil. She says this helps the seed (tubers) to harden their skin in the soil. She reveals that potato farming is good business.

Recommending the seed potato from Kachwekano to other farmers, Akankwansa says they are free of diseases unlike those from other areas which might be infected with pests and diseases.