What Cotton Cultivars have Resistance or Tolerance to Southern Root-knot and Reniform Nematode?

by | Feb 28, 2025 | Cotton, Field Crops, Nematodes, Pest Management

Zane J. Grabau, University of Florida, Associate Professor in Nematology; and Jefferson de Oliveira Barizon, University of Missouri, Graduate Student

In Florida, and the Southeast in general, southern root-knot nematode and reniform nematode are the major plant-parasitic nematodes of cotton. Commercial cultivars with resistance or tolerance to southern root-knot nematode have been available for a number of years, but commercial resistance to reniform nematode was not available until the early 2020’s. Since that time, the number of cotton cultivars with company-denoted resistance or tolerance to these nematodes has increased. The purpose of this article is to summarize these cultivars as a quick reference as well as to provide context about the relationship of these cultivars with plant-parasitic nematodes.

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What is resistance and tolerance?

The terms resistance and tolerance are variously used by agriculture companies to describe the relationship of their cotton cultivars with specific plant-parasitic nematodes. So, what do these terms mean? In Nematology, a resistant cultivar is defined as a cultivar that reduces or prevents reproduction of the target plant-parasitic nematode. The opposite of a resistant cultivar is a susceptible cultivar, and the target nematode reproduces freely on a susceptible cultivar. Tolerance refers to the ability of a cultivar to maintain yield (escape damage) despite the presence of the target nematode. Commercially, when the term “tolerant” is used, it typically implies that the cultivar is susceptible, although technically various combinations of resistance and tolerance can occur. In practice, there is no standard metric for what constitutes a resistant or tolerant cultivar, so the meaning of a “resistant” or “tolerant” designation may vary by company. In particular, cotton resistance to southern root-knot nematode is known to involve multiple genes and the level of resistance varies based on the number of genes incorporated into the given cultivar. Resistance genetics of specific cotton cultivars is typically not readily available.

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How have these cultivars performed against reniform or root-knot nematodes in independent testing?

Given this potential variability in terminology, cotton cultivar performance against nematodes in testing by land-grant Universities, USDA-ARS, or similar independent organizations is an important resource. Due to the wide number of cultivars available, not all cultivars have been tested side-by-side in University nematode trials, although we are working toward more comprehensive testing. In past University of Florida trials, the reniform nematode resistant cultivars tested (DP 2141NR, DP 2143NR, PHY 443, and PHY 411) have been highly resistant and increased yields overall (Figure 1). Most of that research is summarized in the article Resistant Cotton Cultivars and Nematicides Can Help Manage Reniform Nematode.

DP 2141NR was resistant to southern root-knot nematode in UF trials, but we have not tested other cultivars against this nematode. However, many cotton cultivars have been tested against southern root-knot nematode at other land-grant Universities. As mentioned above, the level of resistance to southern root-knot nematode does vary by cultivar, although many recent releases exhibit a high level of resistance. Overall, yield responses for resistant cultivars under southern root-knot nematode pressure tend to be somewhat uneven.  Southern root-knot nematode may be less damaging than reniform nematode and some resistant cultivars may have lower agronomic potential, which probably contribute to this unevenness. For assistance with finding independent testing data for specific cultivars, please contact Dr. Grabau and your County Extension Agent. If you want to see results from other land-grant institutions yourself, linked here is Texas A&M nematode testing in 2022 and 2023 trials. Additionally, from Auburn University, results of many nematode trials that include different cotton cultivars are available as 1-page reports in Plant Disease Management Reports, which requires a subscription.

For local information on performance of various cotton cultivars, see cotton variety trial results from UF WFREC (Jay, FL) in the 2023 report and the 2024 report. Both trials were conducted at sites not selected for nematode pressure.

Figure 1. A reniform nematode resistant cotton cultivar (DP 2143NR right) has greater vegetative growth and canopy closure than a susceptible cotton cultivar (left) in 2024 field trial in Quincy, FL. The field had a severe infestation of reniform nematode.

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Summary of cotton cultivars with company-listed resistance or tolerance to reniform or root-knot nematodes

Now that you have the necessary background, you can refer to Table 1 and Table 2 for cotton cultivars that are listed by the relevant company as tolerant or resistant to southern root-knot nematode or reniform nematode. Table 1 contains cultivars that include the Southeast in the geographic adaptation region listed on the company website. Table 2 lists cultivars where the company-listed adaptation region does not include the Southeast or the region is not specified. Links to company websites that were used as information sources are provided in at the end of the article. While we tried to include all cultivars, lists may not be comprehensive. These resources are provided as a quick guide to assist agricultural professionals that are considering growing a cotton cultivar that is resistant or tolerant to plant-parasitic nematodes.

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Company website information used to compile cotton cultivar tables:

Americot (NexGen) Nematode resistance/tolerance information not listed at time of publication

BASF (FiberMax)

BASF (Stoneville)

Bayer (Deltapine)

Corteva (Phytogen)

DynaGro

 

Zane Grabau
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