Q&A with Craig Yencho: Unleashing the Power of the Sweetpotato Genome

Sweetpotato farmers in Malawi show off the fruits of their labor. New approaches to plant breeding take into account farmer and other stakeholder voices at the start of the breeding process— helping to deliver varieties with their preferred traits. (photo: S. Quinn/CIP)

As program leader of the sweetpotato and potato breeding and genetics programs at North Carolina State University, Craig Yencho is passionate about training the next generation of plant breeders. His students have gone on to transform the sweetpotato world in sub-Saharan Africa. He sat down recently with regional communications specialist Vivian Atakos to discuss the latest innovations in sweetpotato breeding.

VA:  Traditionally, how did breeders develop new varieties with preferred traits such as cooking times or texture? And how, in your opinion, does sequencing accelerate the process of breeding new varieties with these preferred traits?

CY: In the first ten plus years of my career we did things by brute force. We made crosses. We planted populations out in the field. We used various tools to measure yield, disease, resistance, and so on.  Culinary quality and cooking quality are really critical in in sweetpotato. So, we would set up a rudimentary kitchen in our labs to do standardized cooking trials on often several hundred lines. For example, we would measure texture on all those hundred lines and pick the best to cross and then recombine them and plant them out in the field. Slowly, through breeding the population would change in the direction we were interested in. That’s a very slow and time-consuming  process.

In the era of genomics, we can now measure variation at the DNA level and make associations, and associate those traits with the markers, and not really have to go through the long arduous process of growing large populations in a field. They’re a tool that really helps find the needle in the haystack— find the best lines that have the potential to be a good variety and do breeding more efficiently.

VA: Plant Breeding has changed a lot in the last few years. Can you share some of the technologies that are helping breeders target preferred traits and deliver new varieties at a faster pace?

CY:  The biggest things that I wrestle with as a plant breeder and as a trainer of future plant breeders, is harnessing the technologies that are available to us in a fashion that allows us to understand the complexity of sweetpotato. We’re now in an era of Big Data. We use genomic tools to understand genetic diversity of sweetpotato down to the individual base pairs of the sweet potato genome. And when our applied breeders are in the field phenotyping the crop, they’re taking a myriad of measurements on crop performance, using new instruments, and collecting more data than we ever have before. Then we try to make sense and merge our genomic data with our phenomic data to see how traits that we observe in the field are related to genetics, at the sequence level, is a really complex task.

Dr. Craig Yencho (seated center) with a team of plant breeders in Uganda. Streamlining data and plant genotyping is helping to modernize plant breeding and slashing years off the time it takes to produce new and improved varieties. (photo: C. Yencho)

VA: Let’s talk about the sweetpotato product profiles. These take into account the different needs and wants of key stakeholders from farmers to commercial manufacturers. How does the information in product profiles assist you as a breeder?

CY:  Breeding does not occur in a vacuum. It’s really critical we understand all along the path: What does the farmer need? What do the consumers need? How are the farmers responding to those consumers’ needs?  If we’re connected along that that pathway, we’re establishing breeding targets that are relevant, acceptable, and preferred. I think that’s a really great strategy. It helps us stay focused on our goals, what we need to improve, what’s, acceptable in the commercial markets, and how do we get there.

On the other side, though, is that breeders are often very innovative. They because see a wide range of germplasm and might be working on something that consumers aren’t even thinking of right now. So sometimes they will take a risk and try something that is going to be totally different. An example of that is in Sub Saharan Africa, is orange-fleshed sweetpotatoes, which a lot of us have worked on to address vitamin A nutrition. That was an opportunity, breeders and a lot of other visionary people saw for biofortification to address human nutrition problems. So, it’s a little bit of both, you take a guided risk because breeders are a little bit entrepreneurial, but also you stay focused on what the consumers need.

VA: What is the feeling when you finally arrive at that one variety that hits all the sweet spots you’re looking for as a breeder?

CY: It’s kind of like having children. When you watch them take their first steps, or go to kindergarten for the first time, or graduate from high school, and you sit back, and you look at all the hurdles that they’ve come through, and you just have this tremendous sense of pride. But also, it makes you feel really, really humble to have contributed to the success of your son or your daughter. That might be stretching a little bit. But every new variety goes through this process.

Every sweetpotato, and in my other favorite crop potato, is picked as a single unique genotype early on, and then it goes through a series of tasks that take years to accomplish. And when you see them being adopted by farmers, and that it’s used as a source of income that may have even helped to send the farmer’s child to school, you realize that you were part of the process, and there’s a lot of pride behind it.

If you’re a good breeder, there’s a lot of varieties that don’t make it. The ones that eventually do make it really, really are special. But you’re always worried that something is going to go wrong. There’s always a little trepidation. I bring it back to watching your kids go out the door. You are always extremely proud of them, but you’re always still worried about them when they’re walking through life.

VA: What do you think is your biggest contribution to the world of plant breeding?

CY:  I’m really proud of the people that I’ve helped to mentor and it’s not only my students, but a lot of the younger technicians that I meet when travel across the continent (Africa) and help to inspire them a little bit or empower them achieve their dreams. I’m really proud of seeing people succeed. A long time ago, I used this analogy where I said, let’s just build field and increase our knowledge of sweetpotato genomics. And let’s let really smart people come into that field and start to play, to conduct high level research that takes the crop further and further along and helps us to develop new tools to improve the crop. That’s one thing that we’ve done on the genomic tools project, and now under SweetGAINS, is to bring these higher order tools such as genomic assisted breeding tools, to sweetpotato. And along that process, we brought some really smart people from all around the globe to work on it.

These scientists have done things that I hadn’t even thought about, because they bring new ideas and new ways of doing things. It lifts the whole crop and the whole community higher. What’s going to happen next as these new tools come along, new investigators come in because they find it interesting, it’s a productive area to work in and that next generation of breeders starts to kind of take on the reins and do great things. I’m excited about that. And I’d say I’ve had a little bit to do in helping build that field. That’s one of the things I really feel best about it. I think it’s time well spent.

Visit us on SoundCloud to listen to the SweetGAINS podcast featuring Dr. Craig Yencho and other scientists modernizing plant breeding.

This interview has been edited for length and clarity.