New tools to harvest better potatoes

Mercy Kitavi is a geneticist and capacity-building scientist with the International Potato Center based in Nairobi, Kenya.

By Mercy Kitavi

In a traditional African setting, we say that time waits for no man and doesn’t spare the women either.

At exactly 5:30 a.m. in East Africa, the cock crows and Kanini slowly stretches from her rickety-legged wooden bed that is covered by a thin mattress. She knows she is lucky, yet every morning when she opens her eyes to a new day, she feels like closing them again.

Her three children sprawl across a nearby mat, covered with a piece of blanket. She glances at the four goats standing in a corner of their one-room grass-thatched house. They must make room for the children to prepare for school. She takes them outside and ties them to a tree standing tall at the entrance of the house.

Nearby, a heap of fresh red soil covers the grave of her husband who was killed in a recent community conflict over pasture and water.

Quickly she wakes the children and smears their tiny faces with water droplets almost the volume of a single spit. Their feet are left to be cleaned another day.

As if it is an inherited trait, saving water seems to have been instilled in them since conception. It helps spare their mother the agony of walking the whole day in search of water. They gulp a cup of porridge, knowing it probably is the only meal of the day.

Then off they run to school.

The goats stretch their ropes to reach the grass behind the hut. They know that they must eat before the sun is hot and the grass too coarse to chew. After milking the goats, Kanini tethers them to a shadier tree to browse.  But she herself has no respite from the fiery sun as she weeds her field.

She stares at her farm and reminds herself that life is generous to those who pursue their destiny.

Rubona research station in Rwanda. Image: Christine Bukania, International Potato Center.

The thin maize and feeble beans scattered across the farm are drying up. The sweetpotato hills, while weather beaten, are the only green plants, the sole hope for this household of people and goats. But their leaves are mottled, a sign of an unexpected virus. Curious, Kanini digs another hill a few steps away, exposing the larvae of weevils struggling for breath under the hot soil.

She tends to the withering crops just in case luck is on her side and a drizzle of rain appears. She carries a few vines to the goats so that they can cheat their stomachs and survive until the next day.

The gods must be crazy” she sighs, wishing she was an alchemist who understood the forces of nature.

Kanini is an imaginary person representing people I knew while growing up in my village.  But this situation is very real and not unique in sub-Saharan Africa.  More than one quarter of the population suffers from hunger, according to a 2017 report by the United Nation’s Food and Agriculture Organization. Improved policies and programs are needed to reach the agency’s goal to end hunger by 2030.

Kanini’s sweetpotatoes, attacked by insects and viruses as they are, could be a key to reaching that goal. Their roots can be kept in the ground and harvested as a continuous food supply without expensive storage. They are an especially important source of nutrition in the month or two before the major grain harvest, when the grain stored from the previous year is exhausted.

Potato study. Image: Paul Musana, NaCRRI-Uganda

And they are an important hedge for when grain crops fail. Their roots can be boiled, baked, roasted or eaten raw. Their leaves are a good source of protein and vitamins A, C and B2.

Climate change means that sweetpotato is even more important as rainfall is increasingly inadequate, delayed or nonexistent. Hunger rises and livelihoods decline as farming families struggle with multiple droughts. Given the poor nutrition of many children and women, the drought-tolerant sweetpotato is an important food.

But it could be even better. Genetic research can ease the concerns of farmers like Kanini, who worry about disease and pests.

An ambitious effort to harness this research is the Genomic Tools for Sweetpotato Improvement Project. Called GT4SP, project leaders are developing modern breeding tools to improve a crop that already sustains millions of people.

It is led by North Carolina State University collaborating with the Boyce Thompson Institute at Cornell, Michigan State University, the University of Queensland in Australia, the International Potato Center in Peru, Biosciences East and Central Africa in Kenya, the National Crops Resources Research Institute in Uganda and the Crops Research Institute in Ghana.

What distinguishes one plant from another is encoded in its genetic material. Some traits, like flower color, may be controlled by only one gene. More complex characteristics, like crop yield or starch content, may be influenced by many genes.

Traditionally, plant breeders select plants based on their visible traits – their phenotype. The method has successfully improved sweetpotatoes. It helped researchers develop the orange-fleshed sweetpotato varieties adapted to Africa by crossing with the existing local white or yellow varieties. That research won the 2016 World Food Prize.

But conventional breeding is difficult, slow, costly, sometimes subjective and it can be complicated by how the environment influences the plants.

New molecular techniques offer a great opportunity to develop methods that are less subjective and faster at evaluating plants with desirable traits. They can be carried out on seedlings. Scientists don’t have to wait for the plants to fully grow to express desirable or undesirable traits.

And the research is unaffected by the environment, allowing the selection to be done in greenhouses or off-season nurseries. That’s also helpful for improving traits only expressed in favorable conditions.

The researchers look for the genetic clues to a plant’s resistance to disease and insects, and that improve drought resistance and yields. As they discover them, they carefully record what they find.

Genomic tools with no information on how to use them is like having a machine without a manual.

The project has developed a mixed model of training to empower African sweetpotato breeders to translate the research into applied breeding. Workshops combine presentations and hands-on experiences. They are interactive, using exercises, case studies, field visits and other elements of experiential learning.

Webinars are streamed live from partners at Michigan State University and North Carolina University in the U.S. In my village, we say if you have a rich neighbor, you too are rich.

Biosciences eastern and central Africa (BecA) trains African sweetpotato breeders who will become the next generation breeders using these molecular techniques.

Sweetpotato breeding and improvement has come a long way. Researchers conclude that the crop still has great potential to meet the challenges associated with its genetic complexity, new diseases, troublesome pests and climate change.

The new genetic tools they develop may someday ease the plight of farmers like Kanini.

 A version of this story appeared in the Sweetpotato knowledge portal.


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