Scientist starts to sequence 1,000 Guinea yam species

By John Agaba 

August 26, 2022

Yams — or dioscorea — are some of the starchiest tubers consumed in sub-Saharan Africa. They are a source of nutritional and economic importance for hundreds of households on the continent. Yet very little is known about the genetics of this crop, information that is vital to preserving its diversity.

One scientist, however, wants to change this.  

After winning this year’s Illumina Greater Good Grant, Dr. Ranjana Bhattacharjee is on a mission to collect and store genomic information of more than 1,000 Guinea yam species to safeguard the species’ genetic diversity as well as enhance its resilience. 

The molecular geneticist, who is attached to the International Institute of Tropical Agriculture (IITA), will use whole-genome sequencing to understand the crop’s evolution and determine traits that can improve disease resistance and make the varieties more resilient to the effects of climate change.  

“We want to collect genomic information of this important food crop and develop a store of reference genomes that breeders and other scientists can use to develop disease-resistant and higher-yielding yam varieties in developing countries,” says the scientist. 

Although yams are planted all over the world and are the fourth most important root and tuber crop, after potatoes, cassava, and sweet potatoes, the tubers are especially popular in West Africa. More than 90 percent of the crop is grown in a “yam belt” stretching from southeast Guinea to northwest Cameroon.  

“Yams are very important food crops in Africa,” says Dr. Robert Asiedu, former yam breeder in West Africa. “The tubers are important sources of starch and lots of households and children here survive on them.” 

Apart from nutrition and food security, yams are integral socio-cultural symbols in some communities in Africa. For example, among the Igbo of West Africa, yams often play an important role in wedding ceremonies and festivals as they are revered as a symbol of fertility. 

Despite this enormous potential, very little genomic information has been collected about these tubers, in part because of inadequate funding.  

“When I first came to IITA at Ibadan (in Nigeria) in 2019, I realized there was very little research about this very important food crop,” says Bhattacharjee. “There were few scientists studying the crop.” 

She decided she was going to join the few. 

She started preliminary research on the tuber at the IITA labs in Nigeria. But she will now expand her scope to conduct whole-genome sequencing of yam species after winning the Illumina Grant. 

Bhattacharjee and colleagues will work to understand the genetic relationships between different yam species (both cultivated and wild) in West Africa. They will also study specific genes of the crop that can confer disease resistance and resilience and improve yields.

The molecular geneticist will focus on generating DNA sequencing data on yam diversity to accelerate breeding programs to improve food security in many low-income communities on the continent.  The sequencing data will be made public on IITA’s open-access platforms.

Genome sequencing, which is a laboratory procedure for determining the genetic makeup of specific organisms, is revolutionizing agriculture, says Bhattacharjee, who is convinced that the amount of knowledge generated will change the status of this orphan crop. 

Since 2011, Illumina has supported research proposals that can increase the sustainability and productivity of important food commodities and livestock species globally.  

Asiedu says this particular support will help researchers to develop more resilient and disease resistant yam varieties for millions of farmers on the continent. 

Although yams can grow well without fertilizers or herbicides, they must be staked, mounded and routinely monitored for weeds, says Asiedu. But breeders must also continue to develop new varieties or hybrids that can withstand changing weather patterns.  

This process can be long and exhausting. 

But with modern tools and technologies they can isolate targeted characteristics and transfer them from one species to others in relatively short periods. This helps to shorten the breeding process. 

Bhattacharjee says her work will reduce the time it takes to develop new yam cultivars.

“It will also help to identify traits that can provide more clues toward improving the crop through comparative genomics,” she says. “At the end of the day, the goal is to develop more resilient, disease-resistant and higher-yielding crop varieties.”

Image: Dr. Ranjana Bhattacharjee with some of the Guinea yam plants she is working with. Photo: Contributed