An Improved Soybean Cultivar ‘Wonyul’ with Resistance to Phomopsis Seed Decay by Mutation Breeding

Research Article
Article Information

  • Title: 돌연변이 육종에 의한 미이라병 저항성 콩품종 ‘원율’
  • Authors: 김진백, 이경준, 김동섭, 하보근, 김상훈, 송희섭, 강시용
  • Published: September 30, 2013
  • Journal: Korean Journal of Breeding Science
    • Volume: 45
    • Issue: 3
    • Pages: 293-297
  • DOI: https://doi.org/10.9787/KJBS.2013.45.3.293

Abstract


Phomopsis seed decay in soybean is one of the major diseases in soybean cultivation and harvest. Especially, hot andhumid weather in maturing season attribute to the severe loss for soybean seeds by symptom of Phomopsis. To improve thisweakness, seeds of landrace ‘KAS 360-22’ with susceptibility for Phomopsis were irradiated using a 250 Gy gamma ray in 1998.This cultivar has a few distinguishable characteristics such as resistance to Phomopsis seed decay, seed color change and highyielding, compared to landrace ‘KAS360-22’. Although the maturation period of ‘Wonyul’ (127.5 DAS (days after sowing)) is18.9 days later than that of landrace ‘KAS 360-22’ (108.6 DAS), their total yield (233.3 kg/10a) is about 11 times higher thanthat of landrace ‘KAS360-22’ (24.9 kg/10a). Their agronomic trait including resistance to Phomopsis seed decay is much betterthan standard cultivar ‘Ilpumgeomjeong’ for mixed cooking with rice.

Research Background


A. Research Context


  • Soybean Importance: Soybeans are a vital protein source and contain bioactive compounds (e.g., isoflavones, saponins) linked to health benefits like cardiovascular disease prevention.
  • Disease Challenge: Phomopsis seed decay (PSD), exacerbated by hot/humid conditions during maturation, causes seed wrinkling, rot, and yield loss (up to 50% in susceptible varieties).
  • Current Solutions: Farmers rely on fungicides and timely harvesting to manage PSD, but these are costly and labor-intensive.

B. Knowledge Gap


  • Limited Resistance: Traditional breeding struggles to develop PSD-resistant cultivars without compromising yield or agronomic traits.
  • Mutation Breeding Potential: No studies had applied gamma-ray mutagenesis to enhance PSD resistance in the Korean landrace KAS 360-22.

C. Research Objectives


  • Develop a PSD-resistant soybean cultivar via gamma-ray mutagenesis of KAS 360-22.
  • Evaluate agronomic performance (yield, maturation time, seed quality) against the parent line and standard cultivar Ilpumgeomjeong.

D. Significance


  • Economic Impact: Reduces reliance on fungicides and prevents yield loss (~10x higher yield than KAS 360-22).
  • Nutritional Value: Maintains high seed weight (27.5 g/100 seeds) for food applications (e.g., rice-mixed dishes).

E. Additional Context


  • Mutation Breeding: Gamma irradiation (250 Gy) induces genetic diversity while preserving desirable traits.
  • Regional Adaptation: Targets cultivation in southern Korea’s humid climates, where PSD is prevalent.

Materials and Methods


1. Plant Material & Mutagenesis


  • Parent Line: Susceptible landrace KAS 360-22 (yellow seed coat, PSD-susceptible).
  • Mutagenesis:
    • Gamma Irradiation: 1,000 seeds exposed to 250 Gy gamma rays (1998, KAERI).
    • M1 Generation: Irradiated seeds sown to produce 187 M2 plants.

2. Selection Process (2000–2009)


  • Generational Advancements:
    • M2–M6 (2000–2003): Screened 46 mutant lines for agronomic traits.
    • M7–M12 (2004–2009): Progressively narrowed to 1 elite line (KAS360-22-450-1) with:
      • PSD resistance (field assays under high humidity).
      • Brown seed coat (vs. parent’s yellow).
      • High yield potential.

3. Field Trials


  • Locations: Namyangju (2004–2005) → Jeongeup (2006–2009).
  • Design:
    • Plot Size: 3.6 m² (3 × 1.2 m), 60 × 10 cm spacing.
    • Replicates: Randomized complete block design (3 replicates).
    • Controls: Parent KAS 360-22 and standard cultivar Ilpumgeomjeong.

4. Trait Evaluation


  • PSD Resistance: Scored 0–9 scale (0 = resistant, 9 = susceptible) in field infections.
  • Agronomic Traits:
    • Growth habit: Determinate (confirmed visually).
    • Phenology: Days to flowering (DAS) and maturation.
    • Yield: kg/10a (converted from plot weights).
    • Seed Quality: 100-seed weight (g), coat color.

5. Statistical Analysis


  • Data Collection: Followed RDA Guidelines for Crop Variety Trials.
  • Analysis: Mean comparisons (2008–2009 data) using ANOVA.

Key Notes on Methodology


  • Gamma-Ray Advantage: Induced targeted mutations without cross-breeding complexities.
  • Field-Based Selection: Ensured PSD resistance stability under natural disease pressure.
  • Yield Validation: Multi-year/location trials confirmed adaptability to southern Korea.

Results & Discussions


Variety Yield (kg/10a) 100-seed Weight (g) Flowering Period (DAS)† Maturation Period (DAS) Plant Height (cm) No. of nods No. of branches No. of pods Resistance to Phomopsis seed decay (0-9)‡
Wonyul 233.3 27.5 52.8 127.5 46.0 9.3 9.1 43.1 0
KAS360-22 24.9 17.2 44.0 108.6 38.7 7.8 7.4 38.5 7
Ilpumgeomjeong 121.4 27.4 41.6 115.6 35.2 8.9 7.2 35.3 3
†: DAS, day after sowing
‡: 0: Resistant, 9: Susceptible. Every value is shown as the average from 2006 to 2009

1. Successful Development of PSD-Resistant Cultivar


  • PSD Resistance: 'Wonyul' scored 0 (fully resistant) vs. parent KAS 360-22 (7) and standard Ilpumgeomjeong (3).
  • Seed Quality: No fungal colonization or seed wrinkling observed, even under high humidity (Figure).

2. Agronomic Performance


  • Yield: 233.3 kg/10a—10.6× higher than KAS 360-22 (24.9 kg) and 1.9× higher than Ilpumgeomjeong (121.4 kg) (Table).
  • Seed Weight: 27.5 g/100 seeds vs. parent’s 17.2 g (Figure).
  • Maturation Delay: 127.5 DAS (vs. parent’s 108.6 DAS), but with no yield penalty.

3. Morphological Traits


  • Brown Seed Coat: Distinct from parent’s yellow (Figure).
  • Taller Plants: 46.0 cm vs. 38.7 cm (KAS 360-22), aiding light capture (Table).

4. Discussion Points


  • Mutation Breeding Efficiency
    • Gamma Rays effectively induced PSD resistance and seed coat color change without compromising yield.
    • Contrasts with traditional breeding, which often requires trait introgression from wild relatives.
  • Yield Advantages
    • PSD Resistance: Avoids seed loss (~50% in susceptible varieties) and reduces fungicide use.
    • Larger Seeds: 27.5 g/100 seeds enhances marketability for food processing.
  • Trade-Off: Extended Maturation
    • 127.5 DAS may limit cultivation in short-season regions but suits southern Korea’s climate.
  • Comparative Performance
    • Outyielded Ilpumgeomjeong (standard cultivar) by 92%, demonstrating superiority even beyond PSD resistance.
  • Limitations & Future Work
    • Mechanism Unclear: Unknown whether resistance stems from phytoalexin production or structural seed coat changes.
    • Regional Testing: Requires validation in more diverse environments.

Conclusion


1. Disease Resistance Achieved


Gamma-ray mutagenesis successfully converted the PSD-susceptible KAS 360-22 into 'Wonyul', a cultivar with complete resistance (score 0) to Phomopsis seed decay.

2. Yield and Quality Enhancements


  • 10.6× higher yield than the parent line (233.3 vs. 24.9 kg/10a) and 92% higher than the standard cultivar Ilpumgeomjeong.
  • Larger seed size (27.5 g/100 seeds) with a brown seed coat, improving marketability.

3. Trade-Offs Managed


While maturation extended by 18.9 days, the yield gains and disease resistance justify this delay for southern Korean cultivation.

4. Final Statement


This study demonstrates that gamma-ray mutagenesis is a powerful tool to rapidly develop high-yielding, disease-resistant soybean cultivars without compromising seed quality. 'Wonyul' addresses a critical agricultural challenge in humid climates and serves as a model for mutation-assisted crop improvement. Future research should focus on dissecting the genetic basis of its PSD resistance to enable marker-assisted breeding for other soybean varieties.