Updated August 19, 2022:
RESISTANCE TO IMPORTANT SOYBEAN DISEASES
FY 2022 Technical Report for North Dakota Soybean Council
June 30, 2022
Principal Investigator: Dr. Jack Rasmussen, Dept. Plant Pathology, NDSU
Cooperator: Dr. Carrie Miranda, NDSU Soybean Breeder, Plant Sciences, NDSU
The objectives of this research were to work with the NDSU soybean breeder to incorporate resistance to important diseases into soybean cultivars and germplasm for this northern growing area. The emphasis this past year was on 1) verifying and quantifying resistance to sudden death syndrome (SDS) in adapted germplasm for North Dakota and 2) screening NDSU soybean breeding lines for resistance to certain races of Phytophthora sojae, the cause of Phytophthora root rot of soybean, and identify lines with high levels of resistance. Because SDS is a new disease in ND, a focus of the research has been to find resistance in early maturity groups that the breeder could use to begin the development of SDS resistant public soybean cultivars. SDS is expected to spread in the state and become a more important disease in the future.
In May of 2021 a field experiment was initiated to test resistance of a few early maturity soybean varieties for resistance to SDS. The experiment was conducted in microplots on the NDSU experiment station in Fargo, ND. Soil, naturally infested with Fusarium virguliforme, was collected from the upper 15 cm of soil in a field in Richland Co., ND, mixed thoroughly, then placed in 4-liter plastic pots. In one half of the experiment there were 6 varieties tested: Barnes, the susceptible check, (maturity group MG 0.3); Benson (MG 0.4); Bison (MG 0.7); MN1606SP (MG 1.6); ND10-2763 (MG 0.4); and a Pioneer variety as a resistant check (MG 1.5). In a second part of the experiment, two varieties, Barnes and MN0807 (MG 0.8), were compared. The soil was seeded with 12 seeds of a variety, then thinned to 8 plants per pot after emergence. There were 5 pots per variety in a randomized complete block design in each of the two parts of the microplot experiment.
The first group of 6 varieties was planted May 7, 2021, in the greenhouse then moved to the field on June 7. The second group of two varieties was planted May 13 in the greenhouse and moved to field June 8. The pots were buried in the field soil with part of the bottom of the pot removed to allow roots to grow into the field soil (Fargo clay). During the first three weeks of growth the plants were watered daily to maintain moist soil to promote infection and disease development. Because conditions in the field were extremely dry for most of the summer, the plants were watered weekly starting on the fourth week after planting until early August.
The first evidence of foliar symptoms of SDS was in Barnes on July 12. By August 3, all the Barnes plants were showing very strong classic foliar symptoms of SDS. Many Barnes plants died by the third week of august or were partially defoliated. There were also a number of plants in Bison, Stutsman, and ND10-2763 that were showing foliar symptoms by August 3. There were no symptoms yet in Benson, MN1606SP, or Pioneer, the resistant check. In the second group of varieties comparing Barnes with MN0807, on August 5th all the Barnes were showing symptoms but none of the MN0807 had symptoms. Between August 3 to 5th most of the soybean plants in the experiment were in the R4 growth stage. All plants were under stress due to the lack of rain throughout the summer.
On August 19-20, 2021, all plants in the microplot were rated for SDS symptoms using a 1-9 scale: 1) No classic SDS foliar symptoms; 2) < 10% of foliage with chlorotic/necrotic spots; 3) 10-20% of foliage with chlorotic/necrotic spots; 4) 21-40% of foliage with chlorotic/necrotic spots; 5) 41-60% of foliage with chlorotic/necrotic spots; 6) >60% of foliage with chlorotic/necrotic spots; 7) up to 1/3 of plant defoliated; 8) more than 1/3 of plant defoliated; 9) premature plant death. Each plant was rated for SDS and the average score for each variety was determined (Table 1). Two NDSU varieties, Benson and Bison, showed high to moderate levels of resistance and are two candidates for resistance sources for breeding. The two University of Minnesota varieties, MN 1606SP and MN0807, both reported by Minnesota as having resistance to SDS, also showed high levels of resistance in this field test. These are also candidates for sources of resistance. We also verified that Barnes is a reliable susceptible check that will be used in all future SDS studies.
Table 1. Rating of soybean varieties for resistance to sudden death syndrome.
Variety SDS Score Growth Stage
GROUP ONE
BARNES* 7.51 R7
BENSON 1.08 R6/R7
BISON 2.84 R6
MN1606SP 1.25 R6
ND10-2763 4.81 R6
Pioneer** 1.08 R6
STUTSMAN 3.69 R7
GROUP TWO
BARNES 7.06 R6/R7
MN0807 2.31 R6
Plants scored on August 19-20, 2021
SDS scored on a 1-9 scale with 1 = no symptoms and
9 = plants dead.
* Susceptible check
** Resistant check
In addition to the microplot experiments of summer 2021, greenhouse experiments testing resistance to SDS were conducted between during the winter of 2021 to 2022. The methods were similar to those used for the microplot experiments. Soil, naturally infested with F. virguliforme, was collected from the upper 15 cm of soil in a field in Richland Co., ND, mixed thoroughly, then placed in 4 liter plastic pots. There were 4 varieties tested: Barnes, the susceptible check, (maturity group MG 0.3); Benson (MG 0.4); Bison (MG 0.7), and MN0807 (MG 0.8). The soil was seeded with 12 seeds of a variety, then thinned to 8 plants per pot after emergence. There were 5 pots per variety in a randomized complete block design. Seed was planted November 29, 2021, and the evaluation of SDS was on February 22, 2022 using the same 1 to 9 scale as used in the microplot experiments. Barnes had very strong SDS symptoms with an average SDS score of 8 with many dead plants, while Benson and Bison had SDS scores of 2.2 and 2.4, respectfully. MN 0807 however, had an SDS score of 6.8. We had included MN 1606SP in the test, but many plants died from pre- or post-emergence damping-off which was an unusual result and unexpected: therefore, no data was recorded from that cultivar. One of the important outcomes of this research is the identification of good levels of resistance in Benson and Bison, two NDSU soybean variety releases. These can be used as parents for breeding SDS resistance into new NDSU soybean varieties.
In May 2022, another field microplot experiment was started to test SDS resistance of Barnes, Benson, Bison, MN0807 and MN 1606SP using similar methods from 2021. Multiple year testing is needed under various environmental conditions to determine the reliability of the source of resistance. Also, more greenhouse experiments were initiated with the objective to fine-tune a greenhouse screening method using artificial inoculation to test resistance of breeding material to SDS. A greenhouse testing method that would consistently produce SDS symptoms would allow screening to be conducted over the entire year.
In cooperation with Dr. Miranda, the soybean breeder, we screened 180 advanced breeding lines for resistance to Phytophthora sojae during 2022. Most of the screening was for Race 4 resistance since the source of resistance in the breeding lines is probably from the Rps 6 gene. Of the 130 lines tested for race 4 resistance, 80 were resistant. Of the 50 lines tested for race 3 resistance, 14 were resistant. We maintain a variety of races of P. sojae in storage and each year the races we use for screening are grown in the laboratory, inoculated onto a set of soybean varieties with known resistance and susceptibility, and then re-isolated from infected plants to make sure they have maintained their known virulence.
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RESISTANCE TO IMPORTANT SOYBEAN DISEASES
FY 2022 Executive Summary for ND Soybean Council
June 30, 2022
Principal Investigator: Dr. Jack Rasmussen, Professor and Head, NDSU Plant Pathology
Cooperators: Dr. Carrie Miranda, Soybean Breeder, NDSU Plant Sciences.
A major focus of this research was to identify resistance to major soybean diseases in North Dakota and work with the NDSU soybean breeder to incorporate resistance into NDSU soybean varieties. The emphasis this past year was on identifying and verifying resistance to sudden death syndrome (SDS) caused by Fusarium virguliforme, a new disease for our northern soybean production area (Figure 1). In addition, we continued our program of incorporating resistance to Phytophthora root rot into NDSU soybean breeding lines.
In cooperation with Dr. Miranda, the soybean breeder, 180 advanced breeding lines were screened for resistance to Phytophthora sojae during 2022. Most of the screening was for Race 4 resistance since the source of resistance in the breeding lines is probably from the Rps 6 gene. Of the 130 lines tested for race 4 resistance, 80 were resistant. Of the 50 lines tested for race 3 resistance, 14 were resistant. Maintaining resistance in the breeding lines allows new cultivars to be developed with high levels of resistance to certain races of Phytophthora. We maintain a variety of races of P. sojae in storage and each year the races used for screening are grown in the laboratory and tested to be sure they are virulent.
A major effort is underway to identify and verify sources of resistance to sudden death syndrome in germplasm adapted to our northern soybean production area. In 2021 to 2022 various experiments were conducted in both the field and greenhouse to evaluate resistance to SDS in different early maturing varieties (MG 0 to 00). Most of these tests were conducted by growing plants in naturally infested soil until the F6 to F7 growth stage. Resistance was evaluated based on the extent of foliar symptoms of SDS. The testing has identified two NDSU soybean varieties, Benson and Bison, with good levels of resistance to SDS. Other early maturing varieties from MN have also been found to have resistance to SDS. Multiple years of testing is needed to verity that the source of resistance is expressed under various growing conditions. In addition, research is underway to develop screening methods that will consistently result in SDS foliar symptoms under greenhouse conditions. A reliable greenhouse screening method would be a useful tool to identify breeding lines with high levels of resistance and will facilitate development of SDS resistant NDSU soybean varieties.