2019 NPB Research Review

RESEARCH REVIEW

The Pieces Are In Place

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Genetic resources

Genetic knowledge

Breeding

Better peanut varieties

Sponsored by National Peanut Board

RESEARCH REVIEW

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The Pieces Are In Place

e had the genetic resources: wild peanut species in development for millions of years and collected by forward-thinking early plant explorers brave enough to trek into the mountains of South America. We had the breeders: skilled and talented men and women in research labs across the United States and around the world building on the information and experience of prior generations. What the peanut world lacked was the genetic knowledge needed to create better peanut varieties.

That was the missing piece.

When an ambitious plan was put in place to find this missing

information and map the peanut genome, growers were on board. In fact, it is the involvement of peanut growers, shellers and manufacturers that sets this initiative apart.

The peanut genome has been sequenced and analyzed as part of the International Peanut Genome Initiative, funded in part by growers through the National Peanut Board, and that genetic knowledge is no longer a mystery. The future is now.

All the pieces are in place to accelerate breeding progress and get more productive, disease-resistant, stress-tolerant varieties to farmers. Let’s take a look at how all of these pieces will come together for a better peanut.

Looking at wild peanut species, it’s best not to “judge a book by its cover.” Beneath the surface of the straggly plants with small seed is a wealth of genetic diversity. When we get beyond the paltry yield and misshapen pods, what can be found in these long, lost peanut relatives that could be useful in today’s cultivated peanut?

This step in modern peanut breeding may seem to be a step backward, but it was not until the genetics of wild peanut species were mapped that scientists learned many important and helpful genes have been lost along the evolutionary way.

Originating in South America millions of years ago, species in the genus Arachis are found in many diverse environments. More than 80 species have been named, and additional species may exist in some regions of South America even today. Wild Arachis species are highly diverse and contain considerable genetic variability compared to cultivated peanut.

Despite their appearance, early explorers knew wild plant species were valuable. Starting in the 1930s, plant explorers began collecting wild peanut species, along with several thousand land races of the cultivated peanut. These samples were divided into three collections, one each in Brazil, Argentina and the United States. Eventually a copy of all the material was sent to India.

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DAVID J. BERTIOLI, UGA

GENETIC RESOURCES

The genotype of an organism is the genetic code in its cells.

A gene is a stretch of DNA or RNA that determines a certain trait, such as flower color. The visible expression of the trait is called the phenotype. Genes mutate and can take two or more alternative forms, such as the yellow flower and the more orange flower; an allele is one of these forms of a gene.

Researchers are working to determine markers associated with certain traits. In other words, the genes or alleles that correlate to flower color, as in this example.

The United States’ peanut collection is kept at the U.S. Department of Agriculture’s Agriculture Research Service Plant Genetic Resources Conservation Unit in Griffin, Georgia. Combing through this collection for “good” genes using our current genetic knowledge will take time. However, it will seem quick compared to the many years and generations of backcrossing needed when traditional breeding techniques were all that was available. Genomics is turbo-charging peanut research and development.

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GENETIC KNOWLEDGE Genetics of the peanut are complicated. The peanut contains four sets of chromosomes and was too complicated to map. It is described as having an “AABB” genome, with a full chromosome set from two parents. Researchers found the likely parents of the cultivated peanut, Arachis hypogaea, in two wild species A. duranensis and A. ipaensis.

The wild species are diploid with each having two sets of chromosomes. Scientists were able to map the two wild parents and put those together to assist in understanding the genetic code of cultivated peanut.

Sequencing the two ancestors independently gave researchers insight into the peanut we have today. With the sequence of cultivated peanut complete, scientists have begun to look at the genes within the genome and to assign a function to those genes. When the traits of specific genes are known, breeders can more effectively work on those traits.

In the process of sequencing the peanut, researchers discovered markers, a string or sequence of DNA, located near the DNA sequence of the desired gene. Since these molecular markers and the genes are close together on the same chromosome, they tend to stay together as each generation of the plant is produced.

The future direction of peanut breeding is the use of marker-assisted selection to help identify desired genes.

In order to find markers associated with specific traits, both genetic and phenotypic (visual or measurable) data must be gathered and correlated. In a test set of plants designed specifically for identifying markers associated with a certain trait, DNA is taken from each plant and With the advances in molecular peanut breeding, a protocol for sample collection had to be written. As part of a presentation on the Marker Assisted Selection Protocol, University of Georgia’s Peggy Ozias Akins, demonstrates how to perform tissue collection of a folded leaf into a special tube labeled with a coordinating number. This information adds to the genetic knowledge base that will allow peanut breeding to move forward.

Researchers have learned that markers, a string or sequence of nucleic acid that makes up a segment of DNA, are located near the DNA sequence of the desired gene. Since the markers and the genes are close together on the same chromosome, they tend to stay together as each generation of plants is produced. This plot test was a validation of late leaf-spot markers, with the left showing genotypes with resistant markers and the right with susceptible markers.

analyzed. The same plants are examined for the specific trait, for example leaf spot resistance, in the field for a period of years. This is called phenotyping and is necessary to determine which markers correlate to what trait. When the specific markers are always present in plants showing leaf spot resistance, then peanut breeders can use those markers to select leaf-spot resistant plants in their breeding programs. Whatever a peanut plant or seed can exhibit — disease resistance, drought tolerance, reduced skin slippage, improved blanchability — there is a marker for it. Many researchers are working to determine these marker-trait associations in peanut.

Marker Assisted Selection: •

Combines traditional genetics with molecular biology.

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Allows for selection of genes that control traits of interest.

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Is simpler compared to phenotypic screening.

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May be carried out on seedlings or even seed.

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Allows for single plants to be selected with high reliability.

PEGGY OZIAS AKINS, UGA

GRAPHICS BY VECTEEZY.COM

TWITTER: @PEANUTGROWER

NOVEMBER 2019 • THE PEANUT GROWER /

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PeanutBase is the primary genetics and genomics database for cultivated peanut and its wild relatives. Information about genome sequences, genes and predicted functions, genetic maps, markers, links to germplasm resources and maps of peanut germplasm origins is available here. It is a valuable resource for the research and breeding community, funded by the Peanut Foundation and donors of the International Peanut Genome Initiative, including growers through the National Peanut Board.

PEANUT BREEDERS When early man began selecting the healthiest peanut plant with the meatier peanut seed, the peanut breeder was born. Now, peanut breeders work with a wealth of knowledge gleaned over the years from pioneers in the industry.

The rate at which genetic information has increased in just the past decade is impressive, and now a revolution in the peanut industry can begin.

Peanut breeders are seeking to produce higher-yielding, better-quality, lowercost, more sustainable, tasty, healthy peanuts to feed more people. Material is already in the pipeline, a bigger pipeline than before, that will tackle producers’ biggest problems.

Those researchers identifying molecular markers associated with important traits will provide that key information to peanut breeders and researchers who are working to introduce those traits into peanut varieties.

Current peanut varieties are vulnerable to many diseases, drought and other

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environmental stresses. Further, new diseases emerging in countries outside the United States present risks to U.S. peanut production if and when they arrive.

Peanut breeders must work to create cultivars that are resistant to the new diseases to safeguard the U.S. crop.

In Phase II of the International Peanut Genomic Initiative, researchers will start applying what they have learned, and are continuing to learn about the peanut, into new varieties. This research will focus on four key areas—disease resistance, drought tolerance, aflatoxin mitigation and flavor conservation/ enhancement. Improved varieties, and therefore, lower production costs, will benefit everyone in the industry.

With the genetic resources from the germplasm collection and the burgeoning amount of genetic knowledge from the International Peanut Genomic Initiative, peanut breeders have the tools for developing better peanut varieties in less time and with greater precision. RR

International Peanut Genomic Initiative Phase II •

Marker usage in breeding.

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Late leaf spot and other disease resistance.

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Drought tolerance.

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Aflatoxin mitigation.

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Flavor enhancement.

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