Breeding focused on increasing yield and tolerance to new strains of Fusarium Race 4 in California
JOHNSTON, Iowa, Feb. 17, 2026 — PhytoGen® cottonseed, the U.S. cottonseed brand of Corteva, announces a new Pima variety for the 2026 season that combines industry-leading yield potential with increased tolerance to Fusarium Race 4 (FOV4), a fungal pathogen in Pima-growing regions. PhytoGen® brand PHY 859 RF was advanced after breeder and university trials demonstrated consistent high yields combined with excellent fiber quality.
Joel Faircloth, Ph.D., Portfolio Leader, Cotton – Corteva, said PHY 859 RF builds on the success of PhytoGen® brand PHY 861 RF and adds strength to the Pima portfolio. PhytoGen cottonseed is the No. 1 brand of Pima varieties planted in the United States and has a focus on products that meet the demands of California and Arizona Pima acres.
“We’ve tested PHY 859 RF for several years, and it has consistently delivered yields equal to or better than PHY 861 RF, which has set the standard for Pima yields in recent years,” Faircloth said. “But what really elevates PHY 859 RF is its enhanced Fusarium Race 4 tolerance and a slightly higher micronaire, two attributes that Pima growers have told us they want in a variety.”
In PhytoGen breeding trials, PHY 859 RF averaged 1,751 pounds per acre and a 4.3 micronaire – a 13 pound per acre advantage over PHY 861 RF with a 0.1 increase in micronaire.1 Faircloth said PhytoGen continues to support Pima growers through a significant commitment in infrastructure that includes a research facility and breeding team in Corcoran, California.
“Pima is a premium market with unique challenges, and we are very attentive to what our customers want from Pima cottonseed varieties,” Faircloth said. “Fusarium Race 4 is the No. 1 production challenge Pima growers face, so developing varieties with increased tolerance is a strategic priority for us. There’s also a growing demand downstream for a little higher micronaire, and we want to provide our customers with varieties that have the fiber quality characteristics to help meet the demand.”
Dan Gorman, Global Cotton Breeding Lead for Corteva, said the breeding team has focused on FOV4 tolerance in recent years as multiple strains of FOV4 have been identified in California. The PhytoGen team takes tissue samples from Pima plants and isolates FOV4 strains that breeders then use to develop varieties with improved FOV4 tolerance.
“We have data that shows different FOV4 strains coming from California fields, and we utilize those strains in our breeding program as we test for FOV4 tolerance,” Gorman said. “Our breeders evaluate varieties in the field and in our pathology lab, allowing us to do multiple screenings per year to more quickly identify genetic lines with FOV4 tolerance. Through that process, we’ve improved FOV4 tolerance with PHY 859 RF, which provides a better defense against this agronomic threat, improving yield potential.”
PHY 859 RF won the University of Arizona 2025 Pima Cotton Variety Trial at Thatcher, Arizona, yielding 1,403 pounds per acre and beating the trial average by 137 pounds per acre. It also had the best fiber length with a 52 staple and a 4.2 micronaire.2 Kristen Nelson, PhytoGen Product Agronomist for California and Arizona, evaluated PHY 859 RF across different agronomic environments in 2025 and is confident the variety has higher yield and fiber quality potential that growers need to market their cotton.
“It’s exciting to see our focus on both agronomics and market demands. We’re striving to improve yield potential and disease tolerance while also focusing on fiber quality factors, such as micronaire,” Nelson said. “PHY 859 RF fits the production needs of our growers to help growers meet the market demands for high-quality fiber.”
To learn more about PhytoGen brand PHY 859 RF, visit PhytoGen.com.
12023-2025 PhytoGen Breeder Trials, Corcoran, California.
22025 University of Arizona Cotton Variety Trials, Pima trial at Thatcher, Arizona.
PhytoGen® brand PHY 859 RF is the newest Pima variety available from PhytoGen® cottonseed, offering premium yield potential combined with increased Fusarium Race 4 (FOV4) tolerance and improved fiber quality. After extensive testing in breeding and third-party trials like this location in Corcoran, California, PHY 859 RF was advanced for the 2026 season.
For more than 45 years, PhytoGen® cottonseed, the U.S. cottonseed brand of Corteva, has helped growers win in the field with cottonseed varieties that help to maximize yield potential and fiber quality. Growers work smarter with the most advanced trait technologies, such as WideStrike® 3 Insect Protection and the Enlist® cotton trait. Join the discussion with PhytoGen on Facebook, X and YouTube, or subscribe to our monthly Best Yielder eNewsletter.
Corteva, Inc. (NYSE: CTVA) is a global pure-play agriculture company that combines industry-leading innovation, high-touch customer engagement and operational execution to profitably deliver solutions for the world's most pressing agriculture challenges. Corteva generates advantaged market preference through its unique distribution strategy, together with its balanced and globally diverse mix of seed, crop protection, and digital products and services. With some of the most recognized brands in agriculture and a technology pipeline well positioned to drive growth, the company is committed to maximizing productivity for farmers, while working with stakeholders throughout the food system as it fulfills its promise to enrich the lives of those who produce and those who consume, ensuring progress for generations to come. More information can be found at www.corteva.com.