Creation of New Soybean Varieties with High Levels of Resistance to White Mold
Published: 07/20/2023
DOI: doi.org/10.31274/cpn-20230801-0
CPN-5011
CPN 5011. Published July 20, 2023. DOI: doi.org/10.31274/cpn-20230801-0
Richard W. Webster, North Dakota State University; Megan McCaghey, University of Minnesota; Brian Mueller, University of Wisconsin-Madison; Carol Groves, University of Wisconsin-Madison; Febina Mathew, North Dakota State University; Asheesh Singh, Iowa State University; Mehdi Kabbage, University of Wisconsin-Madison; and Damon Smith, University of Wisconsin-Madison.
Summary
Soybean production is consistently threatened by white mold, caused by Sclerotinia sclerotiorum, especially in the Northern soybean growing regions.
Genetically resistant soybean varieties can limit white mold development and yield losses.
We created breeding populations to develop varieties with improved resistance levels to help address the limited number of commercially available white mold resistant soybean varieties.
Through greenhouse and field trials across multiple years, we identified three soybean lines—Marathon (MG: 1.5), Sauk (MG: 2.5), and Rock (MG: 2.9)—that consistently demonstrated resistance to white mold while exhibiting high yields and favorable agronomic traits.
These three newly developed soybean varieties are now commercially available for implementation in production systems with a primary focus on combating white mold. Certified seed of these varieties will be made available through the Wisconsin Crop Improvement Association beginning in 2024. Moreover, these lines are invaluable resources for future breeding endeavors aimed at further enhancing white mold resistance.
Introduction
Soybean production faces persistent threats from the fungal pathogen Sclerotinia sclerotiorum, which causes white mold (Fig. 1). Planting soybean varieties with robust resistance has shown to minimize white mold severity, while also reducing the need for chemical inputs aimed at managing the disease (Webster et al. 2023).
Figure 1. A) Beginning of white mold development typically seen during the early R5 growth stages (beginning of pod fill), B) severe white mold infection which has led to complete plant death prior to complete pod fill, and C) field wide epidemic of white mold which will result in yield losses due to premature plant death.
Soybean resistance to white mold is driven by multiple genes, unlike other types of resistance such as Phytophthora root and stem rot which is determined by single gene resistance (Rps genes; McCaghey et al. 2017, Kandel et al. 2018, Roth et al. 2020). This means that white mold resistance is quantitative and varieties can range from being highly susceptible to highly resistant (Webster et al. 2021). There have been multiple attempts to introduce many of these quantitative resistance genes into a single soybean variety to improve resistance levels against white mold. However, this work has been challenging since some modern breeding tools such as marker assisted selection can’t be used for these types of resistance genes. Further, some white mold resistant soybeans are thought to result in increased lodging because stem integrity can be altered by specific breeding efforts (Ranjan et al. 2019). Despite the challenges associated with this resistance, several research and breeding efforts have been successful (McCaghey et al. 2017, Polloni-Barros et al. 2022).
Despite the success in public breeding efforts for white mold resistant soybeans, the availability of commercial varieties with such resistance remains limited, posing challenges for farmers. Our objectives were to create white mold-resistant soybean varieties suitable for production and to serve as new parental lines for future breeding efforts.
Research Goals
Perform crosses between diverse soybean lines with previously identified white mold resistance.
From the resulting breeding populations, develop new soybean varieties with high levels of resistance to white mold while also maintaining favorable agronomic traits.
Evaluate soybean breeding lines for resistance to additional economically important diseases.
The Research
In 2016, two crosses were made at Iowa State University between white mold resistant parental lines with diverse genetic backgrounds to enhance resistance levels. These crosses involved the combinations 51-23 x 52-82B and SSR51-70 x 51-23. Previous studies by McCaghey et al. (2017) had already identified these three parental lines as having high levels of white mold resistance. The parental lines were originally developed by the University of Wisconsin-Madison, with 52-82B resulting from a cross between W04-680 x AxN-1-55, and both 51-23 and SSR51-70 originating from a cross between W04-680 x W04-1002.
The resulting breeding populations underwent multiple generations of selection, focusing on desirable agronomic traits at full maturity such as minimal lodging, abundant branching, and optimal plant height (Fig. 2). Starting from the seventh generation a total of 25 soybean lines were assessed for white mold resistance in both greenhouse and field conditions. The greenhouse trials followed a protocol described by Webster et al. (2021), utilizing a panel of four soybean check lines for accurate determination of resistance levels in the breeding lines. Field trials took place in Hancock, WI during the 2020 season, and disease development was recorded between the R5 (beginning of pod fill) and R6 (seeds have filled entire pods at one of four uppermost nodes) growth stages. From both the greenhouse experiments and field trials, ten soybean lines consistently demonstrated resistance to white mold (Fig. 3).
Figure 2. Soybean line with favorable agronomic traits including high number of branching from the main stem, little to no lodging at maturity, and adequate plant height.
Figure 3. Screening the 7th generation soybean breeding lines for resistance to white mold under both A, B) greenhouse conditions in Madison, WI between 2019 and 2020 and C) field conditions at Hancock, WI in 2020. Greenhouse trials were conducted by inoculating A) 14 and B) 12 F7 soybean breeding lines and four soybean check lines with standardized resistance levels to S. sclerotiorum with a single isolate of S. sclerotiorum (n = 4). Disease intensity refers to the cumulative development of white mold across three time points under greenhouse conditions. Blue bars represent the breeding lines, and gold bars represent the four check lines. The field trial assessed disease severity index of natural infections of white mold on 25 F7 soybean breeding lines (n = 4). Error bars represent the standard error, and soybean lines sharing similar letters do not statistically differ as determined by Fisher’s least significant difference (α = 0.05).
These ten soybean lines were further tested for white mold resistance in the eight generation through repeated greenhouse and field trials. Additionally, extensive evaluations for agronomic traits, seed quality (protein and oil content), and yield were conducted in replicated field trials across two locations in Wisconsin (Table 1). Through these assessments, three soybean lines—Marathon (Maturity group 1.5), Sauk (Maturity group: 2.5), and Rock (Maturity group: 2.9)—emerged as standouts (Fig. 4). These lines consistently exhibited resistance to white mold, while also delivering high yields and favorable agronomics (Fig. 5). Over multiple generations, these lines were screened for resistance to other soybean diseases, including frogeye leaf spot (caused by Cercospora sojina), Cercospora leaf blight (caused by Cercospora spp.), anthracnose (caused by Colletotrichum spp.), brown stem rot (caused by Cadophora gregata), and stem canker (caused by Diaporthe spp.).
Table 1. Agronomic and quality traits of ten F8 soybean breeding lines and four soybean check lines with standardized resistance levels to Sclerotinia sclerotiorum when assessed under field conditions at Arlington, WI (ARS) and Hancock, WI (HARS) during 2021.u
Breeding Line | Branch-ingv | Height (cm) | 100 Seed Weight (g) | Protein (%)w | Oil (%)w | Yield (bu/ac)y | |||||
ARS | HARS | ARS | HARS | ARS | HARS | ARS | HARS | ARS | HARS | ||
W19-1191 | 1.5 c | 90.8 cf | 86.5 ef | 16.3 h | 13.6 d | 35.0 eg | 36.5 ce | 18.3 e | 18.0 g | 66.4 bc | 33.8 eg |
W19-1273 | 2.3 a | 110.0 a | 101.5 ab | 17.5 fg | 16.6 bc | 38.6 a | 39.2 a | 17.8 f | 17.5 h | 53.0 fg | 42.2 bc |
W19-1331 | 0.1 d | 90.0 cf | 90.3 cf | 18.4 ef | 16.0 c | 35.3 df | 37.1 bd | 19.2 bc | 18.3 dg | 54.5 fg | 38.2 ce |
W19-2335 | 0.4 d | 95.5 cd | 97.0 ac | 20.6 ac | 18.8 a | 35.7 de | 37.2 bc | 19.2 bc | 18.5 ce | 50.7 gh | 37.3 cf |
W19-2336 | 0.3 d | 93.5 cf | 96.3 ad | 20.0 cd | 18.8 a | 35.4 df | 37.5 b | 19.4 b | 18.6 cd | 47.6 h | 35.0 eg |
W19-2379 | 0.5 d | 96.3 bd | 102.5 a | 21.3 ab | 19.1 a | 37.4 b | 38.6 a | 17.8 f | 17.5 h | 53.8 fg | 37.1 cf |
W19-2409 | 0.3 d | 91.3 cf | 94.0 be | 20.3 bc | 17.6 b | 34.8 fg | 36.5 ce | 19.5 ab | 18.9 b | 53.9 fg | 35.6 df |
Marathon | 1.3 c | 93.3 cf | 88.8 df | 20.7 ac | 17.7 b | 36.6 c | 36.3 df | 18.2 e | 18.5 ce | 60.2 de | 29.8 g |
Rock | 2.1 ab | 97.3 bc | 98.3 ab | 19.2 de | 17.5 b | .x | .x | .x | .x | 62.2 cd | 41.0 bd |
Sauk | 1.4 c | 95.0 ce | 87.8 ef | 16.6 gh | 14.3 d | 35.7 de | 36.7 ce | 18.2 e | 18.1 fg | 61.6 ce | 32.2 fg |
51-23z | 0.6 d | 86.0 f | 96.3 ad | 19.1 de | 16.8 bc | 35.4 df | 36.4 df | 18.8 d | 18.3 df | 57.4 df | 37.1 cf |
52-82Bz | 1.8 ac | 103.5 ab | 96.8 ac | 18.3 ef | 17.3 b | 36.6 c | 37.8 b | 18.4 e | 18.2 eg | 69.7 b | 48.7 a |
Dwightz | 1.6 bc | 88.8 df | 89.0 df | 15.8 h | 14.4 d | 34.5 g | 35.7 f | 19.1 cd | 18.7 bc | 76.5 a | 45.1 ab |
SSR51-70z | 0.1 d | 87.8 ef | 83.8 f | 21.5 a | 17.7 b | 36.0 cd | 36.1 ef | 19.8 a | 19.5 a | 56.2 ef | 37.3 cf |
u Values represent the mean value from two replicated field trials with four replicates from each site-year. Trials were performed in 2021 at Arlington, WI and Hancock, WI.
v Branching scores were measured by approximating the mean number of lateral branches per plant in each plot.
w Protein and oil contents were measured using an NIR analyzer meter.
x Due to the black seed coat of Rock, the NIR analyzer meter could not approximate a value for protein or oil.
y Yield was measured at the end of the season and adjusted to 13% moisture.
z Soybean check lines with standardized levels of resistance to white mold. Dwight is highly susceptible to white mold, 51-23 and SSR51-70 are moderately resistant to white mold, and 52-82B is highly resistant to white mold.
Figure 4. Screening the 8th generation soybean breeding lines for resistance to white mold under A) greenhouse conditions in Madison, WI between 2020 and 2021 and B) field condition at Hancock, WI in 2021. Greenhouse trials were conducted by inoculating soybean breeding lines and four soybean check lines with S. sclerotiorum (n = 8). Disease intensity refers to the cumulative development of white mold across three time points under greenhouse conditions. Blue bars represent the breeding lines, and gold bars represent the four check lines. The field trial assessed for white mold developmenton ten F7 soybean breeding lines and four soybean check lines (n = 4). Soybean lines sharing similar letters do not statistically differ as determined by Fisher’s least significant difference (α = 0.05).
Figure 5. Seed of each of the three new soybean varieties with high levels of resistance to white mold.
Marathon, the earliest maturing variety among the three, features black hilum color and demonstrated low levels of lodging and shorter plant height compared to other evaluated lines. It also displayed moderate resistance to both Cercospora leaf blight and brown stem rot. Sauk, with a clear hilum, achieved the highest yields and exhibited low lodging scores, short plant heights, and high resistance levels to frogeye leaf spot and brown stem rot. Rock, a black-seeded soybean, shows potential as a specialty variety highly valued in many East Asian markets due to the dark color of the seed. It showcases high degrees of branching and resistance to anthracnose, Cercospora leaf blight, and brown stem rot, along with moderate resistance to frogeye leaf spot.
Conclusion
The development of three new soybean varieties—Marathon, Sauk, and Rock—offers promising solutions for both farmers and breeders. These varieties exhibit high levels of resistance to white mold, favorable agronomic traits, and show potential for commercial production. With their ability to combat multiple economically important diseases and deliver high yields, Marathon, Sauk, and Rock provide valuable options for farmers seeking improved soybean cultivars. Furthermore, these varieties serve as valuable parental lines for future breeding efforts, allowing breeders to further enhance white mold resistance and develop new varieties tailored to specific regional needs.
This research update is based on the work described in the following peer-reviewed research articles
Webster, R. W., McCaghey, M., Mueller, B., Groves, C., Mathew, F. M., Singh, A., Kabbage, M., and Smith, D. L. 2023. Development of Glycine max Germplasm Highly Resistant to Sclerotinia sclerotiorum. PhytoFrontiers. DOI:10.1094/PHYTOFR-01-23-0009-R. Article / Google Scholar
References
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Acknowledgements
Authors
Richard W. Webster, North Dakota State University; Megan McCaghey, University of Minnesota; Brian Mueller, University of Wisconsin-Madison; Carol Groves, University of Wisconsin-Madison; Febina Mathew, North Dakota State University; Asheesh Singh, Iowa State University; Mehdi Kabbage, University of Wisconsin-Madison; and Damon Smith, University of Wisconsin-Madison.
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