Peanut Genomics Bring the Future Closer: Q & A with Dr. Corley Holbrook

By: Lindsay Stevens

There’s a quote that goes, “many hands make light work.” When we think teamwork, rarely is the first image in our mind research. But the collaboration being done by Dr. Corley Holbrook, a USDA supervisory research geneticist, has brought new meaning to this old phrase. Through his work with collaborators like Dr. Peggy Ozias-Akins and Dr. Ye (Juliet) Chen, Holbrook estimated they annually genotype (1) over 15,000 seeds using genetic markers. This work has and will continue to lead to scientific breakthroughs, including Holbrook’s latest advancement. Recently, a peanut variety was developed using genetic markers resistant to leaf spot. This development could lead to reduced or eliminated spraying for leaf spot.

NPB: What made you interested in this type of research?

When I first started my position in Tifton, I decided a large part of my research would be directed toward breeding peanuts for disease resistance. I screened most of the U.S. germplasm collection for leaf-spot resistance in field studies and for peanut root-knot nematode resistance in greenhouse trials. Unfortunately, the collection of cultivated species only contained moderate levels of resistance to these pathogens. More recently, we got access to genes for resistance from related wild species and this has been a game-changer. For example, Dr. Charles Simpson introgressed (2) genes for near immunity to the peanut root-knot nematode, and in the past 15 years, we have used those genes to develop four peanut varieties that are nearly immune to this nematode. More recently, we have begun to use genes for leaf-spot resistance from wild species. We plan to release varieties with high-resistance levels to leaf spot this year.

NPB: You are known for collaborating with other researchers at other institutions. How did that come about?

I greatly enjoy doing peanut breeding and genetic research. I had excellent mentors early in my career that showed me the more I cooperated with other scientists, the more research I could be involved in. Therefore, I have tried to surround myself with as many collaborative scientists as I could find. This has been a huge win for me. I also try to make sure it is a win for them. Usually, it works out that way.

NPB: What have been the benefits of collaborating with other researchers?

I will answer this question with a real-life example. Dr. Peggy Ozias-Akins started her career in Tifton, Georgia, a few years after I had started. Part of her research assignment was molecular-genetic research in peanut. We have been seeking opportunities to collaborate since her start, and for several years, these opportunities were limited due to the primitive (relative to other crops) state of genetic technology in peanut. In 2008, Ozias- Akins made research breakthroughs that enabled us to begin using marker-assisted selection (MAS) in the breeding program. Our research progress was also greatly facilitated by the addition of Dr. Ye (Juliet) Chu to our team. We all were active in the International Peanut Genome Initiative, and that research has also greatly impacted our breeding program. Because of the advances in technology, and our collaborative team approach, we annually genotype over 15,000 seeds using genetic markers for several traits. This provides over 50,000 data points and has had a tremendous impact on our breeding program.

NPB: How did you go about discovering the trait and getting it into a breeding line?

Leaf-spot resistance was first introgressed into the cultivated species by Dr. Tom Stalker at North Carolina State University several decades ago. This germplasm traveled around the globe and recently made it into some breeding lines in Brazil. I was cooperating with the peanut breeder in Brazil, and we exchanged some breeding lines in a cooperative research project looking at resistance to tomato spotted wilt virus (TSWV). Drs. David Bertioli and Soraya Leal-Bertioli alerted me that one of these breeding lines may have the introgressions from Tom Stalker’s material. We checked and it did have three introgressed genetic regions. A graduate student (Samuele Lamon) did a study to document the importance of each of these regions on leaf-spot resistance. We also began an accelerated backcross breeding program using MAS to develop leaf-spot resistant varieties.

(L-R); Dr. Corley Holbrook, USDA-ARS, Tifton; Dr. Steve Brown, Executive Director of the Peanut Research Foundation; Bob Parker, National Peanut Board; Dr. Peggy Ozias-Akins, University of Georgia, Tifton.

NPB: What does this new leaf-spot-resistant variety mean to farmers?

If we are successful, this leaf-spot resistance will mean fewer trips across the field for farmers and reduce the use of fungicides. This will save time and money and, hopefully, increase profits.

NPB: Will farmers have to give up yield or other traits for this leaf-spot resistance?

All our currently available data indicates that they will not. We have several breeding lines with excellent resistance to leaf spot along with yield and grade that is at least as good as commonly grown varieties. We are working with Dr. Marshall Lamb at the National Peanut Research Laboratory to conduct an economic analysis to determine which combinations of variety and fungicide input will result in maximum profitability. A successful peanut variety must also meet a range of quality attributes. We are currently gathering data on those attributes to ensure that these varieties will maintain the high quality that the U.S. peanut crop is known for.

The National Peanut Board (NPB) has allocated more than $37.9 million toward state and industry production research projects, including work led by Holbrook. For a searchable database of NPB-funded projects, visit PeanutResearch.org.

1 Genotyping is a DNA analysis to determine the genes present in a plant to determine if the plant is a suitable parent for future breeding.

2 Introgression is the transfer of genetic material from one species into the gene pool by repeated breeding of a specific hybrid with one of its parent species. In this case, the trait was bred in from wild species.