Small-scale farmers in developing countries use the potatoes harvested on their farm as potato seed. Or those obtained from neighbors or local markets. But this material usually has pests and diseases which accumulate from one cycle to another. And that often diminish the crop yields. Researchers have known this process as seed degeneration. A recent study recommends combining three tactics to mitigate this problem. This paper analyzes the seed degeneration, details the proposed strategy and describes five simple techniques to improve seed quality.

Update: How to Control Potato Late Blight by Using Fungicides Correctly | Using a new tool, small-scale farmers can now know what kind of fungicide to use and when and how often to apply it. More at https://bit.ly/2ErG4UQ

Versión en español

The potato is the third most important food crop in the world after rice and wheat on human consumption. And more than half of its production occurs in developing countries.

Potato consumption per capita in developing countries tripled (from 6 kg in 1969 to 18 kg in 2014) due to:

• potential yield of the crop
• high nutritional value
• culinary diversity

The short time that needs the potato crop to produce food allows it to reduce famines. Besides, it can grow alongside other crops or interspersed with them, as happens with cereals in Africa and Asia.

But yields are low in developing countries.

And one of the main causes is the seed degeneration.

What is the seed degeneration?

Seed degeneration is the reduction of yield or quality caused by an accumulation of pests and diseases throughout successive cycles of vegetative propagation.

It has been a limiting factor in most potato production areas of the world.

Developed countries solved the problem providing their farmers with continuous access to certified seed (Formal Seed Systems).

Developing countries tried to do the same, but the results have not been as expected. Today the use of certified seed is minimal there.

Small-scale farmers use their potato seed. Or get it from neighbors and local markets (Informal Seed Systems).

Informal seed systems comprise all activities related to the production, management, and use of seed. Most of their farmers are Small-scale farmers. Formal systems cover the same events, but public and private sector supervised them. Small-scale farmers produce informal seed on the farm. Or get them from neighbors or in local markets. Specialized farmers produce and sold the formal seed. Public institutions regulate them through seed certification programs.

What are the causes of seed degeneration?

Any pathogen that affects the quality of potato seed, and can accumulate into it, contributes to its degeneration.

But viruses are the main culprits, in particular, the so-called PVX, PVY and PLRV.

Their infection capacity varies according to geographic distribution and height above sea level.

A study determined in Ecuador that the virus incidence was less than 3%. And that pathogens such as Rhizoctonia solani, Streptomyces scabies, and pests such as Premnotrypes vorax were more important.

Another research in the Andes mentions that degeneration decreases to heights greater than 2,800 meters.

Some authors include the physiological defects into the causes of the seed degeneration. But unlike pests and diseases, these are not transmitted to neighboring crops nor reappear due to improper management.

How to manage seed degeneration?

The CGIAR Research Program on Roots, Tubers, and Bananas (RTB) has been analyzing the problem since 2012.

In a recent article, RTB examined the results of research carried out in Latin America, Asia, and Africa.

One of its recommendations was to re-define the problem of potato seed.

That is, to stop thinking that the main problem of small-scale farmers is the low access to certified seed.

And rather focus on improving the quality of their seed.

In other words, that the main problem now is the seed degeneration itself.

The article also suggests implementing the following tactics:

• varieties resistant to pests and diseases that cause degeneration
• techniques carried out by the farmer on their farm, and
• occasional use of good seed produced off the farm

Their integration would simplify the management of seed degeneration of the informal seed systems in developing countries.

Each of these tactics is detailed below.

Varieties resistant to pests and diseases that cause degeneration

It is the “smart” way of controlling the problem.

If variety is resistant to pathogens or pests that cause degeneration, those will never accumulate in the plant.

Or they do it at a slower speed.

And the crop yield does not decrease.

Or it does it slowly.

That is why clones released by the International Potato Center (CIP, by its acronym in Spanish) are resistant to the main viruses that affect the potato.

Some clones are resistant to late blight caused by Phytophthora infestans.

But there are still no sources of resistance to Ralstonia solanacearum (bacterial wilt), a primary cause of degeneration.

These clones are available for all the national potato programs. They are the agencies responsible for releasing varieties, after gathering the requirements of each ministry of agriculture.

Techniques carried out by the farmer on his farm

Any management method that controls pathogens in seed would be reducing seed degeneration.

But a preliminary research in Kenya showed that the two most effective methods are seed plot and positive selection. Both of them combined with the use of certified seed.

(Because they are complementary techniques, author present them as one)

1–2. Seed plot and positive selection

Seed plot and positive selection are techniques that improve the farmer seed reserve.

The process follows these steps:

• Selection of the best plants (positive selection — see below)
• Storage of the harvested tubers of that selection
• Planting of the tubers in the seed plot

In each crop cycle, it is necessary to repeat those steps.

Farmers use the remain tubers for their consumption.

It is not necessary to discard plants (negative selection) but doing so improves the efficiency of the techniques.

Seed plot and positive selection are effective practices because:

• Are done quickly and at low cost
• they contribute to maintaining the quality of good seed produced on the farm
• they increase the crop yield, especially when there are viruses

The farmer must be able to identify healthy plants and be familiar with the symptoms of the diseases.

CIP published in 1983 the document On-farm seed improvement by the potato seed plot technique (PDF).

Likewise, CIP released in 2007 the paper Select the Best: Positive Selection to Improve Farm Saved Seed Potatoes (PDF).

3. Plastic barriers

The Andean Potato Weevil (Premnotrypes vorax) is one of the primary pests of the potato crop in the Andean region.

This insect is present in the field and storage all year round. So, farmers control it both at planting and after harvest.

CIP is promoting the use of plastic barriers to control the weevil at the time of planting.

Weevil walks to the fields to colonize them because it can not be flying. Then, a physical barrier would have to be enough to prevent them from entering.

In fact, CIP trials it with farmers show that a plastic cloth 30–50 cm high was more efficient and cheap than insecticides.

4. Seed drying in the sun

The Guatemalan moth (Tecia solanivora) is a pest that currently is in:

• Central America ( Costa Rica, El Salvador, Honduras, Nicaragua, Panamá)
• South America (Colombia, Ecuador, Venezuela, and Peru)
• Spain (The Canary Islands and Galicia Autonomous community)

It is a pest that can damage all tubers stored for seed.

The tubers affected by the Guatemalan Moth carry the larvae of the moth inside. And the sun forces them out of there.

This technique reduces up to 50% damage to the tubers, according to CIP trials.

The treated tubers should be used as seed and not for human consumption because the sun turns green the tubers and that gives them a bitter taste.

The Autonomous National Institute of Agricultural Research (INIAP, by its acronym in Spanish) of Ecuador published in 2005 the bulletin Potato Seed drying in the sun (Spanish) as a control measure for Tecia solanivora.

5. Silo to green potatoes

Small-scale farmers accustom to store the tubers in silos with indirect lighting and free air circulation. One of the benefits of this practice is to make the tubers turn green. A greenish tuber it is more resistant to attack by insects and soil fungi.

A small-scale farmer can use farm materials to build silos of simple design and low cost.

INIAP of Ecuador published in 1986 a bulletin that shows how to do it: Silo to green potatoes, cheap method to store potato seed (PDF).

Occasional use of good seed produced off the farm

Farmers in developed countries change their seed in each cycle. Then, seed degeneration is not a problem for them.

In developing countries, it is not the same. Farmer’ potato seed usually degenerates, and it is necessary to renovate it regularly.

To know when do it depends on factors such as:

• variety
• crop conditions, and
• seed management

When degeneration can not handling with resistant varieties or farm techniques, it is necessary to buy a good seed the farm.

But countries can regulate or not the seed production for sale.

If the country regulates it, traders refer it as “certified seed.”

If it is not, traders refer it as “seed without official control.” And their sale can lend itself to deception.

The non-conventional seed systems become necessary at the last situation.

Non-conventional seed systems integrate both informal systems and formal systems. That is to say, they use seed produced on a farm, but they control their quality in a rigorous way. Then, the product is a good potato seed. Even with quality standards like those of the certified seed.

An example of Non-conventional seed systems is Conpapa in Ecuador.

Summary and conclusions

In potato cultivation, the seed is a determining factor for its yield.

But potato seed is a large seed, difficult to transport and store, perishable, with a low rate of multiplication and expensive.

That is why small-scale farmers in developing countries use part of the tubers harvested as the seed for the next cropping cycle.

Or they buy it and trade it them in local markets.

It is a situation that causes a gradual loss of crop yield due to the accumulation of pathogens in the seed.

The farmers and scientists know this process as seed degeneration.

Until today they believed that the only tactic to manage the seed degeneration was the use of certified seed.

But it is not.

A study of the CGIAR Program of RTB shows that it is one of the tactics.

The others are varieties resistant to pests and diseases that cause degeneration and techniques to improve the quality of the farmer’s seed

Their combination would allow the management of seed degeneration in informal seed systems in developing countries.

The RTB Program is currently conducting studies to corroborate this strategy.

To do that, they use simulation models in many environments, using different varieties and management techniques.

With these models, scientists will develop decision support systems. So, small-scale farmers will be able to choose the best tactics to manage the seed degeneration.

But that happen when ministries of agriculture, universities and nongovernmental organizations, change their policies related to potato seed production.

They must:

• Increase the investment in genetic improvement to generate and disseminate varieties resistant to the primary pathogens and pests that cause degeneration
• Enable producers to improve the quality of their seed, and
• Help them access to good seed, preferably certified seed.

For now, a tool for interventions in seed systems would ease this process.

It is a conceptual framework that analysis the seed systems to design, install and test interventions.

So, everything is ready.

It is time to change.

And do not continue to think that the only solution to the seed degeneration is to use certified seed.

Because in the end, the goal is improving the living conditions of small potato producers.

And overcome a paradigm.

The paradigm of the use of certified seed!