California Fights To Beat Fusarium Wilt Race 4

Christi Chadwell
Christi Chadwell

An increasing topic of conversation between researchers and producers at area meetings across the Cotton Belt is Fusarium wilt race 4 (FOV4) — a fungal disease that is difficult to control in cotton and can survive in soils indefinitely.

With vital support from Cotton Incorporated, scientists in California have been investigating resistance to FOV4 since 2003 when the disease was first confirmed in the San Joaquin Valley.

But, for many other researchers, such as those in Texas, this seems to be a relatively new threat. With the identification of FOV4 in far West Texas in 2017, researchers have placed urgency on breeding, genetics and molecular approaches to resistance.

Collaborative Research Effort

When the disease emerged in the San Joaquin Valley, the U.S. Department of Agriculture-Agricultural Research Service research stations in California, in conjunction with the University of California, worked tirelessly to improve resistance in Pima cotton.

Researchers studied what made these Pima lines more resistant than the Upland cotton varieties. They also increased the genetic base for FOV4 resistance and identified more tolerant breeds. Pima cotton varieties with high FOV4 resistance ultimately replaced Upland cotton in California fields.

fusarium wilt race 4
This cotton plant shows vascular root staining, one of the symptoms of FOV4 fungal disease.

Research has found that measuring the foliar symptoms, root vascular staining and plant mortality of affected cotton plants shows that affected Upland cotton is generally less severe than the affected Pima cotton. Understanding that FOV4 might look different in Pima and Upland cotton is key in understanding how to diagnose the disease in the field.

Since 2013, several thousand breeding entries have been developed at California research stations that show signs of resistance or tolerance. Currently leading these research efforts are Drs. Mauricio Ulloa with ARS, Robert Hutchmacher with the University of California, Margaret Ellis with California State University, Fresno, and Philip Roberts with the University of California, Riverside.

With funds from Cotton Incorporated, California Cotton Ginners and Growers Association, and the California Cotton Alliance, they are developing new breeding lines in Upland cotton. Without the research partnerships and much of the early work started in California years ago, the outlook for dealing with FOV4 would not be as optimistic.

“Our approach has involved introducing tolerant genes from identified Upland tolerant lines from our research from ARS Cotton Germplasm Collection and the University-Breeding Programs,” Ulloa says. “From 2006 to 2018, we have been evaluating Upland germplasm or breeding lines from about 13 public cotton breeding programs across the Belt through the regional breeder testing network sponsored by Cotton Incorporated.”

An Eye On Texas

Significant improvement and progress has been made through these research initiatives since FOV4 was discovered. While there has been a push to incorporate tolerant Pima cotton into several farming operations in California, the threat of FOV4 is still looming since most Pima varieties aren’t suited for other U.S. growing regions.

With the recent diagnosis in far West Texas, the opportunity for the disease to spread throughout the rest of Texas is daunting.

Ulloa is now lending his expertise to the Texas area experiencing the disease. The strides he has made with other California researchers could be crucial to countering FOV4. Current research is analyzing California cotton fields to isolate the disease and identify better cotton lines that demonstrate higher resistance to FOV4.

Educational Material

With support from Cotton Incorporated, the California Cotton Growers and Ginners Association, and the California Cotton Alliance, these researchers were able to publicly release for-purchase tolerant or resistant Pima cotton lines, first in 2008 and again in 2016. Recently, they have identified Upland cotton entries that should have tolerance to FOV4, with the hope they could be released to the public in late 2019 or 2020.

To educate producers, Cotton Incorporated, with the help of industry partners, has released a FOV4 fact sheet, including the “quick test” guidelines developed in California to identify the disease in the field.

It also describes safe practices to help avoid FOV4 contamination. The document provides crucial information to growers as they use and purchase seed and equipment from other areas of the Cotton Belt.

To view the FOV4 publication, go to

Christi Chadwell is the Cotton Board’s regional communication manager for the Southwest. Please contact her at

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