Wild relatives of modern peanuts can withstand disease in ways modern peanuts can’t. Genetic diversity of these wild relatives means they can tolerate diseases that kill farmers’ peanut crops. They also produce tiny nuts that are difficult to harvest. During development, modern peanuts lost genetic diversity and an ability to fight off fungus and viruses. However, qualities that make peanut productive, affordable, sustainable and tasty were enhanced so that people all over the world grow and eat them.
Modern peanut plants developed 5,000 to 10,000 years ago. Two diploid ancestors — plants with two sets of chromosomes — combined and became tetraploids, containing four sets of chromosomes. Cultivation of domesticated peanuts spread around the world now appear in foods from Asia to Africa to the Americas. The diploid relatives remain restricted to their origins in South America.
Researchers at the University of Georgia, particularly at the Wild Peanut Lab in Athens, have been studying the genetics of wild relatives and detailing where beneficial traits are located within the genomes. The goal is to understand the advantageous ancient genes, lost in modern peanuts in order to combine them while retaining modern traits that farmers need and consumers want.
“Most of the wild species still grow in South America,” said Soraya Leal-Bertioli, who runs the Wild Peanut Lab with her husband, David Bertioli. “They are present in many places, but you don't just come across them on the streets. One has to have the ‘collector's eye’ to spot them in the undergrowth.”
Wild plants can’t breed with peanut in nature any longer because they only have two sets of chromosomes.
“The wilds are ugly, distant relatives that peanut does not want to mix with,” Leal-Bertioli said, “but we do the matchmaking.”
Researchers in Athens and Tifton have successfully crossed some of those wild species together, resulting in tetraploid lines that can be bred with peanut. New lines give plant breeders genetic resources that may lead to new varieties with disease resistance and increased sustainability.
The Journal of Plant Registrations published the details about the first of these germplasm lines this month. The new lines developed by the Bertiolis are resistant to early and late leaf spot, diseases that cost Georgia peanut producers $20 million a year, and root-knot nematode, a problem that few approved chemicals can fight.
The second set of new varieties come from work done in Tifton and led by Ye “Juliet” Chu, a researcher in Peggy Ozias-Akins’ lab within the College of Agricultural and Environmental Sciences Department of Horticulture. These three varieties are made from five peanut relatives and show resistance to leaf spot. One is also resistant to tomato spotted wilt virus, a disease that nearly ended peanut cultivation in the U.S. in the 1990s.
Creating fertile allotetraploids allows scientists to cross them with peanut and select beneficial traits. Plant breeders will be able to take these lines made from peanut’s wild relatives and cross them with modern domesticated peanut to get the best of both — a plant that looks like peanut and produces nuts with the size and taste of modern varieties, but that has the disease-fighting ability of the wild species.
Crossing the wild species with cultivated peanut led to a line that is 25% wild and 75% cultivated. Additional breeding will yield plants with small seeds, weak pegs, sprawling growth pattern and low yield, but using genetic mapping, breeders can exceptional plants that carry disease-fighting genes and attractive market traits.
“We plan to perform genetic mapping with these materials and define the beneficial wild genomic regions for molecular breeding,” Chu said. “We still need to define the genomic regions in the synthetic allotetraploids conferring desirable traits and specifically integrate those regions into cultivated peanuts.”
With genetic markers, breeders not only can tell that a plant has a desirable trait, they know what genome regions are responsible for that trait and can combine DNA profiling with traditional field selection to speed the complex process of developing a new variety.
“It streamlines everything. You can make a cross, which produces 1,000 seeds, but before planting them, their DNA can be profiled. That way you can see that only 20 of those plants are ideal for further breeding. Forty years ago, you’d have to plant them all, making the process much more cumbersome. In the past, we knew where we were going, but it was like everyone drew their own map,” Bertioli said. “Now, it’s like we have GPS. (Scientists) can tell each other, ‘Here are my coordinates. What are yours?’ And all the data is published.”
Roger Gates is the agricultural and natural resources agent for University of Georgia Extension, Whitfield County. Contact him at email@example.com.