DNA fingerprinting uncovers exactly who and why farmers use improved cassava

“There were a group of samples that didn’t have a reference in our gene bank,” said Ricardo A. Labarta, Senior Scientist and Agricultural and Environmental Economist, who designed the study.

Published recently in the Journal of Agricultural Economics, the study aims to enhance advice to cassava farmers on how to better manage their crops, as well as to measure the impact of the work of CIAT, specifically on cassava.

Together with Corpoica*, CIAT has produced 16 improved varieties of cassava over the last eight years.

Identifying varieties

A key component of the study was to identify cassava varieties that farmers in the Cauca Department were cultivating.

In general, there are two types of crop varieties.

First are landraces. These are plant species commonly cultivated in an area, or the standard variety in a particular locality. There are hundreds of cassava landraces in Colombia. The most popular are called Sata, Algodona, and Amarga.

Second are improved varieties, products of scientific research work with the goal of enhancing the traits of a particular landrace, to make them higher-yielding and more resistant to disease.

In Colombia and elsewhere, farmers obtain these varieties through formal means, such as from extension workers — those who provide advice on crop management. Or they acquire planting materials through informal channels, such as from fellow farmers.

Previous research examining adoption of improved varieties hinged on surveys of farming households. The questionnaires typically ask what farmers grow, which specific crop varieties, how they manage their crops, and what they do with their harvests, among other things.

But verifying the identity of varieties through these surveys has proven to be a challenge. Farmers are often unable to determine varieties by official names or they offer names that are different from the ones on the government records.

There’s also the issue of genetic identity loss. This happens when farmers crossbreed different varieties giving birth to new, undocumented ones.

To address the challenge, Labarta et al added a novel technology to the mix: DNA fingerprinting.

Genetic profiling

DNA fingerprinting analyzes the genetic characteristics or the unique identity of organisms, in this case cassava. For plants, leaves are generally the best source of DNA material.

To do DNA fingerprinting, Labarta’s team had to collect stems of cassava from farmers’ fields. They labeled the samples with the names provided by farmers, and the sites where they were collected. They sent these to CIAT laboratories, which planted the stems in greenhouses. Once the plants had grown, geneticists extracted DNA from the leaves.

From the 434 stem samples from 217 farmers, DNA fingerprinting identified 120 varieties, 9 of which were improved.

Analysis also found disparities in perceived and actual use of landraces and improved cassava. Roughly 17 percent of the households surveyed said they were cultivating improved varieties, but DNA profiling discovered that about 9 percent actually did so. Conversely, some families thought they were planting landraces when in fact they were using improved varieties.

It means DNA fingerprinting gives a clearer picture of the adoption of CIAT-bred varieties.

Why farmers adopt improved varieties

The analysis also offered insights as to why farmers adopt improved cassava.

Based on household surveys or the self-identification method, the following factors mainly influenced decisions by surveyed farmers to adopt improved varieties:

• Number of dependents. Improved varieties yield more cassava and therefore supply more food to family members.
• Total land area. More land provides farmers with enough space to experiment or take risks on a new variety.
• Access to extension services. This enables farmers to have information they need to properly manage and know the advantages of cultivating improved varieties.

Results from DNA fingerprinting, though, show a different picture. The lack of landownership, as per the analysis, was the most important factor. In other words, the biggest adopters of improved varieties were those who were renting lands.

“Because if it’s not your land, you have pay for the rent, so you need to do something that’s going to guarantee a higher income,” said Labarta.

Next steps

The experience in Cauca has inspired Labarta and his team to apply DNA fingerprinting to more impact studies.

In a few months, they will release results of similar research on cassava in Vietnam. They have also started doing a study, again on cassava, in the Caribbean coast of Colombia. Both studies involve a thousand farmers.

There are also plans to expand the use of the technique for other crops, such as beans.

“DNA fingerprinting allows us to measure better CIAT’s contribution to the world,” Labarta said. “Identifying exactly what farmers are planting is essential. The next step is to ensure proper dissemination of improved varieties. Because if farmers use these varieties, it’s going to change their lives as they are guaranteed to produce more, make more money, and improve their food security.”

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Additional information

The paper, Household Determinants of the Adoption of Improved Cassava Varieties using DNA Fingerprinting to Identify Varieties in Farmer Fields: A Case Study in Colombia, is published in the Journal of Agricultural Economics. It was funded by the CGIAR Research Program on Roots, Tubers and Bananas and the Global Human Development Program at Georgetown University.

* Corpoica stands for Corporación Colombiana de Investigación Agropecuaria. It’s a decentralized public nonprofit that focuses on developing and carrying out agricultural research and technology transfer.