New PHY 859 RF boosts yield fiber quality and FOV4 tolerance
PhytoGen® cottonseed, the United States cottonseed brand of Corteva, has announced a new Pima cotton variety for the 2026 growing season. The new variety, PHY 859 RF, combines strong yield potential with improved tolerance to Fusarium Race 4, also known as FOV4. This fungal disease is one of the biggest challenges for Pima cotton growers, especially in California and Arizona.
“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,” said Joel Faircloth, Ph.D., Portfolio Leader, Cotton. “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.”
The company stated that Fusarium Race 4 remains the number one production concern for many Pima growers. Multiple strains of the disease have been identified in California fields. To address this issue, breeders collected plant tissue samples, isolated different FOV4 strains, and tested new genetic lines in both field conditions and laboratory screenings. This process helped improve tolerance in PHY 859 RF, offering better protection and yield stability.
“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,” said Dan Gorman, Global Cotton Breeding Lead for Corteva.
“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,” said Gorman.
The new variety also performed well in independent testing. It won the University of Arizona 2025 Pima Cotton Variety Trial at Thatcher, Arizona. In that trial, it yielded 1,403 pounds per acre, surpassing the average by 137 pounds per acre. It also recorded strong fiber length and desirable micronaire levels.
Company agronomists believe the new variety supports both agronomic needs and market demand. As Pima cotton serves a premium market, growers require strong disease tolerance along with high fiber quality. PHY 859 RF is designed to meet these expectations and strengthen the company’s Pima portfolio for the future.
“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,” said Kristen Nelson, PhytoGen® Product Agronomist for California and Arizona. “PHY 859 RF fits the production needs of our growers to help growers meet the market demands for high-quality fiber.”
Photo Credit: PhytoGen-logo