Most Mid-South farmers have never heard of nor had to worry about Race 4 Fusarium (FOV4) – yet. It is a fungal disease of cotton that spreads through seed or soil transfer, is native to Asia but was discovered in cotton fields in California around 2000. It adversely affected some cotton fields in the San Joaquin Valley, and appears to be moving via Pima cotton seed.
“This is not your mother’s Fusarium wilt,” stated Dr. Bob Nichols, senior director, Agricultural and Environmental Research, Cotton Incorporated, at this year’s Conservation Systems Conferences held recently in Memphis, Tenn. “FOV4 typically attacks cotton in the 4- to 6-leaf stage, leaves smoking holes in cotton stands and doesn’t need nematodes to be transferred into the plant’s roots as do several other fusarium races.”
Since then, it has moved into a few of the most western counties in the Rio Grande Valley of Texas. It takes time for the very resilient and extremely small spores carrying this disease to build up to a point where they can be readily observed to cause damage to a field of cotton. They can also be spread through normal production practices like cultivation or irrigation water.
Although certain Western cotton breeders have successfully bred high levels of tolerance into extra-long-staple (ELS or Pima) cotton varieties, no upland cultivars are known to have proven resistance to FOV4. “It’s an inoculant density-dependent disease, so if the inoculum level is low, you’ll have few or possibly mild symptoms,” says Nichols. “More than likely, levels will increase in subsequent years and growers will see an increase in plant damage.”
The thing that should really concern Mid-South producers is if their fields become heavily infested with FOV4, they can forget about growing cotton on them for a long time.
“That’s why we are being proactive to establish research projects to address this problem,” says Dr. Kater Hake, vice president, agricultural and environmental research, Cotton Incorporated. “We are supporting projects to assist with the identification and control of FOV4 in certain Western states, and we understand it will take a collaborative effort with industry, USDA-ARS, and land grant scientists across the Cotton Belt to get ahead of FOV4.”
Breeding and seeds
Dr. Jenny Koebernick, assistant professor, Auburn University, is a soybean and cotton breeder. She attended the breakout session where Nichols and Louisiana farmer George LeCour Jr. spoke because she is eager to hear Cotton Incorporated’s plans to address this disease.
She has been working to develop lines which exhibit resistance to target spot. “Breeding for resistance to target spot and breeding for resistance to FOV4 are similar because there are no known resistant lines for either of the two diseases,” explains Koebernick.
In addition to U.S. Pima breeders having successfully bred tolerance into ELS lines, cotton breeders in Australia have developed lines with resistance to highly-virulent FOV biotypes that occur there as well. “These results are promising in that breeders should be able to create tolerance or resistance in upland varieties. “It’s not so much if it will happen, but when,” adds Koebernick.
Hake and Nichols understand the potential devastation FOV4 could bring to the Mid-South. They say growers and consultants could initially confuse its symptoms with Rhizoctonia at an early stage. “Staining of the cotton tap root’s vascular tissue, turning it to a continuous brown down to the tap root is typical of FOV4,” adds Nichols. “If a producer sees this damage, I recommend further evaluation.”
Ninety-five percent of U.S. seed production is conducted in the West and Southwest, but principally in Arizona where FOV4 has not been found. Nichols is currently developing a research project to address specific aspects of this fast-spreading disease. “We’ve got to get ahead of this before it impacts more fields than it already has,” says Nichols. “If something isn’t done, this disease will continue to spread.”
Nichols will be working with Western cotton pathologists and agronomists to send out alerts to producers. He advises all producers to verify with their seed dealers that the seed they are buying has been produced in fields that have not been exposed to FOV4. “Many dealers in the eastern part of the Cotton Belt may not be informed about this disease, but growers need to ask,” concludes Nichols.