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SCN Population Effects on SDS and Soybean Yield

 

SCN Population Effects on SDS and Soybean Yield

Background and Rationale

  • Several research studies have shown an association between soybean cyst nematode (SCN) and sudden death syndrome (SDS) in soybean, where SDS symptoms and subsequent yield loss tend to be worse in areas where SCN is also present.
  • Soybean cyst nematode is present in every major soybean producing county in Michigan.
  • The presence of SDS has been positively confirmed in 25 counties across Michigan as of 2013 (Figure 1).

Figure 1. Michigan counties and year of SDS confirmation, based on
research funded by Michigan State Univ. Project GREEEN and Michigan
Soybean Promotion Committee.

Map: Michigan counties and year of SDS confirmation.
 

Objectives

  • A 3-year field research study was conducted as part of the DuPont Pioneer Crop Management Research Awards (CMRA) Program with Dr. Martin Chilvers, Michigan State University.
  • The objectives of this study were to evaluate:
    • Performance of Pioneer® brand soybean varieties with differing levels of resistance to SCN and SDS.
    • The interaction between SCN and SDS in their effects on soybean yield in Michigan.
    • SCN reproduction on soybean varieties with different resistance sources.

Study Description

  • Research trials were conducted from 2011 through 2013 in a field near Decatur, Mich., with heavy SDS pressure and initially low to moderate SCN pressure.
  • 4 Pioneer brand soybean varieties with differing SCN resistance sources and SDS resistance levels were compared in 2011-2012, with 2 more varieties added in 2013 (Table 1).
  • An SCN HG test conducted in 2011 determined the presence of SCN type 2,5,7 (P188788; P1209332; P1548316) at the trial location.

Table 1. SCN resistance source and SDS resistance ratings of Pioneer brand soybean varieties used in the trial.
 Variety / Brand¹  Years used   SCN resistance   SDS resistance  
92Y53(RR) 2011-2013 Peking 6
92Y51 (RR) 2011-2013 PI88788 6
92M82 (RR) 2011-2013 None 3
92Y91(RR) 2011-2013 None 5
93Y20(RR) 2013 PI88788 7
92M75(RR) 2013 Peking 5
 

Measurements

  • SDS symptoms were rated using the standard university rating system of disease incidence (DI) on a 0-100% scale and 1-9 disease severity (DS) scale to derive the disease severity index (DSI), where DSI = (DS/9) x DI.
  • Soil samples were collected just after planting and harvest each year for SCN qualifications.
  • Foliar SDS development was monitored throughout the season with reported ratings taking place at or around R6 growth stage as symptoms peaked.
Photo: Differences in SDS symptoms between soybean varieties in a research study.
Differences in SDS symptoms between soybean varieties in a research study near Decatur, Mich.; Aug. 17, 2012.
 

Results

  • In all 3 years of the study, an increase in SCN numbers during the growing season was associated with soybean varieties with no SCN resistance (Figure 2).
  • Although SCN reproduction was lower on varieties with PI88788 than those with no SCN resistance, it was much higher than SCN reproduction on Peking resistance.
  • In a lab test at the start of the study, the SCN population was found to be type HG 2.5.7, indicating that SCN had broken resistance to the PI88788 resistance source; results that were reflected in SCN reproduction in the field.
  • The Peking resistance source resulted in no net increase of SCN numbers in 2011 (Pf/Pi = 1.01) and even reduced the moderate to high SCN numbers in 2012 and 2013, with Pf/Pi ratios of 0.08 to 0.23 across years and varieties.

Figure 2. Soybean cyst nematode juvenile + egg counts for the beginning and end of each season.

Chart: Soybean cyst nematode juvenile + egg counts for the beginning and end of each season.
 
  • The SDS pressure at the field location was very high when first observed in 2009, with a 50% yield loss reported by the grower.
  • Soybean varieties with Peking SCN resistance developed the least amount of foliar SDS symptoms (Table 2).
  • Varieties with PI88788 resistance sources developed intermediate levels of foliar SDS symptoms, while those with no SCN resistance developed the greatest SDS symptoms.

Table 2. Soybean varieties and SDS disease index by year.
 Variety / Brand¹ SCN / SDS
 Resistance 
 SDS Disease Index** 
201120122013
92Y91 (RR) None / 5 50.5 b 50.9 b 49.8 a
92M82 (RR) None / 3 98.0 a 76.3 a 75.6 a
92Y51 (RR) PI88788 / 6 0.7 c 9.8 c 23.8 b
92Y53 (RR) Peking / 6 0.9 c 0.0 c 0.0 d
93Y20 (RR) PI88788 / 7 -- -- 5.0 c
92M75 (RR) Peking / 5 -- -- 0.3 d
** Values with a column followed by the same letter are not significantly different at α = 0.05.
 
  • The comparison of Pioneer® varieties 92Y91 and 92M75 in 2013 clearly shows the importance of SCN resistance in managing SDS. Both varieties are rated a 5 for SDS (moderate resistance) but 92M75 has Peking SCN resistance, and had greatly reduced levels of SDS compared to 92Y91 which has no SCN resistance.

Table 3. Grain yield of soybean varieties by year.
 Variety / Brand¹ SCN / SDS
 Resistance  
  -------- Yield** -------- 
 2011   2012   2013 
  ------ bu/acre ------
92Y91 (RR) None / 5 25.1 c 12.7 c 25.2 c
92M82 (RR) None / 3 12.0 d 5.8 d 12.8 d
92Y51 (RR) PI88788 / 6 43.4 b 31.0 b 38.3 b
92Y53 (RR) Peking / 6 48.9 a 44.3 a 56.9 a
93Y20 (RR) PI88788 / 7 -- -- 37.1 b
92M75 (RR) Peking / 5 -- -- 56.2 a
** Values with a column followed by the same letter are not significantly different at α = 0.05.
 
  • Yields of some varieties were very low due to the heavy SDS disease and SCN pressure
    (Table 3).
  • Pioneer varieties 92Y53 and 92M75, which have Peking SCN resistance and moderate resistance to SDS, outperformed all other varieties, including those with PI88788 SCN resistance.
  • Pioneer variety 92Y91, which also has no SCN resistance but has moderate resistance to SDS, yielded significantly better than Pioneer variety 92M82, but still far less than the other varieties.

Conclusions

  • Overall, results of this study showed that SCN management is a critical component of reducing symptoms and yield loss associated with SDS.
  • Varieties with the appropriate SCN resistance source for the races present in the field (Peking, in this case) and moderate to high genetic resistance to SDS consistently produced the greatest yield.
  • Knowing the SCN population type and matching the correct genetic resistance can help reduce SDS and SCN injury.


Research conducted by Dr. Martin Chilvers, Michigan State University, as a part of the DuPont Pioneer Crop Management Research Awards (CMRA) Program. This program provides funds for agronomic and precision farming studies by university and USDA cooperators throughout North America. The awards extend for up to 4 years and address crop management information needs of DuPont Pioneer agronomists, Pioneer sales professionals and customers

PIONEER® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents. Do not use these or any other data from a limited number of trials as a significant factor in product selection. Product responses are variable and subject to a variety of environmental, disease, and pest pressures.  Individual results may vary.

2011-2013 data are based on average of all comparisons made in one location through Nov. 1, 2013. Multi-year and multi-location is a better predictor of future performance. Do not use these or any other data from a limited number of trials as a significant factor in product selection.

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