Saturday, July 31, 2021

Field performance of 40 varieties in a southern RKN-infested field, 2020

• By Michael Emerson, Travis Faske and Jesse Kelly •

southern root-knot nematode galls
Southern root-knot nematode galls on a soybean root — photo courtesy University of Arkansas

The southern root-knot nematode (Meloidogyne incognita) is the most important yield-limiting plant-pathogenic nematode that affects soybean production in the mid-South. It is found in nearly all soybean-producing counties in Arkansas and can cause significant (>70%) yield loss when the wrong soybean variety (i.e. susceptible) is planted in a field with a high population density of root-knot nematodes.

During the 2020 season, the Lonoke Extension Plant Pathology Program selected 40 soybean varieties that were divided into five experiments based on herbicide technologies and maturity groups. Varieties were planted in a randomized complete block design with four replications into a loamy to sandy loam soil near Lonoke, Arkansas.

Plots were planted at a seeding rate of 150,000 seeds per acre following corn. Eight root systems were sampled from each plot to determine percent root galling at the R5-R6 growth stage. The final nematode population densities (Pf) collected at harvest ranged from 290 – 719 second-stage root-knot nematode juveniles (J2)/100 cm3 soil, which would be a moderate to severe threshold in Arkansas.

The Pf counts are considerably higher than in 2017 because most of the plants didn’t mature early, thus the peak nematode population occurred when samples were collected at harvest. Percent of root system galled was estimated for at least eight root systems from each replication per test at R4-R5 growth stage.

In general, soybean varieties in each category with the lowest gall rating contributed to the greatest yield; however, there were a few tolerant varieties that had high galling and good yield (Table 1-5). Soybean varieties with <4% of root of system galled are considered resistant compared to those with the greatest galling percentage.

For example, GoSoy 49G16 is resistant compared to Delta Grow DG4880 (2.8/36.8). Field performance of soybean varieties from previous trials (2016, 2017 and 2018) can be found on this website or on the UA Research Series website.

These results and those on the UA variety testing website can be helpful for variety selection for the 2021 cropping season.

Michael Emerson , Dr. Travis Faske and Jesse Kelly are with the University of Arkansas.

Download “2020 Selected Soybean in RKN Field”

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