Tolerance of soybean varieties to white mold

In 1996, the Iowa State University (ISU) Plant Pathology Department conducted tolerance tests of soybean varieties to white mold. The tests were conducted again this year, with funding support from the Iowa Soybean Promotion Board. Sixty-four entries were used from public and private sectors.

The experiments were conducted in field sites in Ames, Kanawha, and Mason City that had severe disease in 1996. Because of drought or hail injury, white mold incidence was light in Ames and Kanawha, and only the site at North Iowa Community College in Mason City had severe disease symptoms.

The field plots in Mason City were planted in mid-May. Each variety was replicated four times in plots four rows wide and 12 feet long with a row spacing of 15 inches. Plots were separated by a border row of the soybean variety Kenwood. Disease and yield data were collected on September 12 and 19, respectively. Maturity information was obtained from various publications, including Soybean Disease-Resistant Varieties for Iowa (Pm 1649).

See the table below for a list of the 1997 varieties and tolerance results. We used a few varieties as checks for tolerance, susceptibility, and moderate susceptibility/tolerance. Tolerance of each variety was measured as the percentage of plants killed. The fewer plants killed for a variety, the higher the tolerance. Keep in mind that the number of plants killed differed from location to location and from year to year because of variation in environmental conditions and farming practices.

This year, the results show greater variability in the relationship between plants killed and yields than did our 1996 results. When choosing a soybean variety, try to select one that is consistent over years and locations, or that seems to perform well for growers in your area. So far, we have noted the failure of two varieties under field conditions, although these varieties did very well in ISU and company tests.

Keep in mind that yield losses are not significant when the percentage of plants killed is less than 20 percent. Depending on how conservative you want to be, varieties with less than 30 percent plants killed can be considered as having acceptable tolerance. In fields with mild disease pressure, varieties that did not receive a high tolerance rating in our test may do well, because our fields had higher disease pressure than did most production fields.

It is important to note that varieties in later maturity groups often have greater disease levels because our test was done in northern Iowa, a region that is outside of their range of normal adaptation. These varieties should have higher yields and less disease when grown in southern Iowa. See the web page at http://www.exnet.iastate.edu/pages/plantpath/whitemold.html for our 1996 results.

1997 White Mold Variety Evaluation Results

NIACC Research Plots



By XB Yang and Michael Uphoff

Department of Plant Pathology, Iowa State University

Company Variety Severity** Maturity*** Av bu/ac
Asgrow Seed Co. AG1901 1 1.9 47.2
Asgrow Seed Co. AG2501* 12.5 2.5 46.4
Asgrow Seed Co. A2704 62.5 2.7 42
Cenex/LOL L1984 17.5 1.9 52.8
Cenex/LOL L2126 38.8 2.1 38.7
Cenex/LOL L2309 10.8 2.3 51.3
Custom Farm Seed CFS 181 21.3 1.8 48.5
Custom Farm Seed CFS 191 3.8 1.9 48.7
Dairyland Seed Co. DSR-173 7.3 1.7 46.2
Dairyland Seed Co. DSR-220/STS 25 2.2 45.5
Dairyland Seed Co. DSR-277 55 2.7 41.3
DEKALB Gen Crp. Cx 197 17.5 late 1 44
DEKALB Gen Crp. Cx 228 22.5 early 2 48.7
Golden Harvest Sds. H-1184 21.3 1 47.6
Great Lakes Hybrids GL1559 1.5 1.5 53
Great Lakes Hybrids GL1872 5 1.8 49.4
Growmark, Inc. HT261 21.3 2.6 46.5
Growmark, Inc. HS 2561 27.5 2.5 49.2
Growmark, Inc. HT 221 13.8 2.2 45.8
Hy-Vigor Seeds Hy-Vigor 1150 6.8 1 44.4
Hy-Vigor Seeds Hy-Vigor 2025 51.3 2 46.8
Latham Seed Co. 250 Brand 15 1.8 52.4
Latham Seed Co. 480 Brand 13.8 1.9 48.5
Lewis Hybrids 276 52.5 2 39.9
Lewis Hybrids 310 73.8 3 35.6
LG Seeds LG 6288 68.8 2.8 35.4
LG Seeds LG 6245 63.7 2.4 33.1
Mark Seed Co. MRK 9519 18.7 1.9 47.7
Merchmann Seeds Cheyenne V 51.2 2.6 41.1
Merchmann Seeds Mars IV 45 1.9 43.6
Midwest Seed Gen. G1885 35 1 46.5
Midwest Seed Gen. G2750 14.2 2 52.3
Novartis Seeds Inc. S19-90 2 1.9 47.9
Novartis Seeds Inc. S20-91 6 2.2 48.8
NC+ Hybrids NC+1A88 48.7 1.8 40.8
NC+ Hybrids NC+2A15 53.7 2.1 41.4
Ottlie Seeds 8206 25 2 44.7
Pioneer Hi-Bred 9163 1.2 1.6 46.3
Pioneer Hi-Bred 9305 9.2 3 42.9
Prairie Brand Seed PB-194 21.2 1.9 50.7
Prairie Brand Seed PB-167 17.5 1.7 49.1
Prairie Brand Seed PB-192 2.2 1.9 47.3
Profiseed PS2035 8 1.9 51.6
Profiseed PS1997 2.5 1.9 48.9
Renze Hybrids R2098 33.2 2 47
Renze Hybrids R1996 40 1.9 38.7
Renze Hybrids R2698 53.7 2.6 39.4
Sand Seed Service SOI 260 21.2 2 46.6
Sand Seed Service SOI 370 45 3 31.2
Terra International TS194 28.7 1 48.3
Terra International TS223 55 2 33.9
Terra International TS286STS 67.5 3 21.6
Thompson Seeds T-3184 3.7 1 54.7
Thompson Seeds T-3193 20.5 1 48.3
Wilson Seeds Inc. Wilson 2252 22.2 2.5 47.1
Wilson Seeds Inc. Wilson 2883 73.7 2.8 29.9
Wilson Seeds Inc. Wilson 1920 46.2 1.9 39.3
BSR 101 12.5 1.9 44.1
Tolerance control Corsoy 79 10.5 2.1 40.9
Tolerance control Dassel 1.5 1.1 40.3
Moderate tolerance control Bell 35 1.6 34.1
Moderate tolerance control Kenwood 40 2.1 39.6
Susceptible control A2242 60 2.2 40.5
Susceptible control Williams 82 86.2 3 13.4

* Roundup Ready variety. No Roundup was applied in our test.

** Severity is percentage of plants killed by white mold taken on 9/12/97, average of 4 plots.

*** Maturity information is from different publications, not from this experiment

Each cultivar was replicated 4 times with plots of 4 row wide and 12 feet long. Row spacing was 15". Yield data were taken from center rows of each plot.

This project was funded in part by the Iowa Soybean Promotion Board.

This article originally appeared on pages 193-194 of the IC-478(25) -- December 15, 1996 issue.

Updated 12/14/1996 - 1:00pm