Susceptibility and Yield of Fifty-six Soybean Varieties to the Southern Root-knot Nematode, 2024

by Michael Emerson, Brandon Baker, Nicole Emerson, and Travis Faske - November 14, 2024

The southern root-knot nematode (Meloidogyne incognita) is a major threat to soybean production and is the most yield-limiting plant-pathogenic nematode that affects soybean production in the Mid-South. It is found in nearly all soybean counties in Arkansas and can cause significant (>70%) grain yield losses when a susceptible variety is planted in a field with a high population density of southern root-knot nematode (RKN). 

In this study, 56 commercially available soybean varieties marketed as suitable for production in southern RKN fields were screened.  Varieties were divided into 4 experiments (Table 1 to 4) based on maturity group.  Varieties were planted in a randomized complete block design with four replications per entry.  Plots consisted of 4 rows, 30 ft long, spaced 30 in. apart, and separated by a 5-ft fallow alley.  Plots were planted on 7 June at a seeding rate of 150,000 seeds/A.  Six root systems were arbitrarily sampled at the R5 growth stage from non-harvest rows of each plot used for assessing southern RKN host susceptibility.  The final nematode population (Pf) density averaged 648 second-stage juveniles (J2)/100 cm³ soil at harvest for susceptible checks across all experiments.  This density is considered severe for soybean production in Arkansas. The post-harvest threshold for southern root-knot nematode on soybean in Arkansas is J2 60/100 cm³ soil. The two center rows of each plot were harvested on 15 Oct (maturity group IV) and 21 Oct (maturity group V).  These results and those on the UA variety testing website can be helpful for variety selection for the 2025 cropping season.  

Reports from previous trials (2016 to 2023) are available on the UADA website at https://www.uaex.uada.edu/farm-ranch/pest-management/plant-disease/publications.aspx   

What else is important: Overall, the severity (percent of root system galled) was lower than last year, so the screen was not as good as in 2023. For example, Delta Grow ‘DB46XF54’ had a gall rating of 51.1% (VS) in 2023 and 16.4% (MS) in 2024.  However, and overall, selecting a variety that is less susceptible will ensure a greater yield than a more susceptible one in a nematode infested field. For example, Pioneer ‘P46Z53E’ would have a lower gall rating and greater yield than Delta Grow ‘DG46E30’, but not Revere ‘48-F72’, if planted in the same field. Consult the cross-reference guide for soybean varieties to ensure different varieties selected are not the same genetics.

Why is final nematode population density or “Pf” important? The timing for these samples would be comparable to fall nematodes samples collected in commercial fields. Therefore, soybean varieties would expect to perform similarly when the nematode population density AND soil texture class (e.g., sandy loam) was similar. Overall, individual varieties will show a greater percentage of root system galled or susceptibility when grown in soils with a greater percentage of sand and nematode densities that are similar to the final nematode densities reported here.  Furthermore, and more importantly, grain yield for individual varieties will decrease with increased drought stress AND when nematode densities are similar to that reported.

Table 1. Field performance of several MG IV soybean varieties in a southern root-knot nematode infested field. The soil texture was sandy loam soil (51% sand, 47% silt, and 3% clay).  (Pf = 576 second-stage juveniles/100 cm³ soil.)

Table 2. Field performance of several MG IV soybean varieties in a southern root-knot nematode infested field, experiment 2. The soil texture was silt loam soil (37% sand, 59% silt, and 5% clay). (Pf = 1,227 second-stage juveniles/100 cm³ soil.)

Table 3. Field performance of several MG V soybean varieties in a southern root-knot nematode infested field, experiment 3. The soil texture was sandy loam soil (49% sand, 49% silt, and 3% clay).  (Pf = 469 second-stage juveniles/100 cm³ soil.)

Table 4. Field performance of several MG V soybean varieties in a southern root-knot nematode infested field, experiment 3. The soil texture was silt loam soil (41% sand, 57% silt, and 3% clay).  (Pf = 320 second-stage juveniles/100 cm³ soil.)

If you have any questions, please contact tfaske@uada.edu