Diagnosis and Evaluation of Root-knot Nematode Damage in Medicinal Plants (Adenophora triphylla and Heracleum moellendorffii) = 약용작물 잔대(Adenophora triphylla)와 어수리(Heracleum moellendorffii)의 뿌리혹선충 감염에 따른 피해 진단 및 평가

다국어 초록 (Multilingual Abstract)

Root-knot nematodes (RKNs, Meloidogyne spp.) are major pathogens causing significant yield losses in global agriculture; however, early diagnosis is challenging as damage primarily occurs underground. This study was conducted to identify RKN species infecting Adenophora triphylla and Heracleum moellendorffii in major cultivation areas of Gangwon-do, develop a non-destructive diagnostic model using image-based vegetation indices, and elucidate biochemical defense mechanisms associated with host responses.
Field surveys identified Meloidogyne hapla as the dominant species in the cultivation sites. In artificial inoculation experiments, the two crops exhibited distinct host responses. Adenophora triphylla showed a highly susceptible response to M. hapla, characterized by severe wilting and biomass reduction. Conversely, H. moellendorffii demonstrated a tolerance response, maintaining limited growth damage despite supporting high nematode reproduction, and showed a recovery pattern following initial damage caused by M. incognita.
Among the multispectral indices, the Normalized Difference Red Edge (NDRE) was the most reliable indicator of nematode-induced stress. While the Normalized Difference Vegetation Index (NDVI) and the Visible Atmospherically Resistant Index (VARI) were confounded by phenological stages such as early leaf senescence in H. moellendorffii, NDRE consistently reflected physiological status, showing the highest correlation with measured Soil Plant Analysis Development (SPAD) values (chlorophyll content). Notably, pot-level continuous monitoring was more effective than leaf-level analysis for assessing cumulative structural damage and reduction in vegetation fraction.
In density-dependent experiments, nematode damage did not increase linearly with inoculum density but plateaued above an intermediate level (1,000 eggs), indicating a saturation effect attributed to the limited carrying capacity of the pot environment. Analysis of biochemical defense mechanisms revealed that while the total flavonoid content (TFC) decreased in the susceptible A. triphylla after infection, it increased by approximately 9–10-fold in the tolerant H. moellendorffii compared with control. This suggests that induced flavonoid synthesis serves as a key tolerance mechanism buffering against oxidative stress.
Conclusion, this study demonstrates that NDRE is a robust imaging indicator for the early detection of RKN damage in medicinal crops and provides physiological evidence for host-specific tolerance mechanisms through secondary metabolite analysis. These findings offer a foundation for sustainable production management and the development of eco-friendly strategies, focusing on early detection and the practical application of control measures.

국문 초록 (Abstract)

뿌리혹선충(Meloidogyne spp.)은 전 세계 농업 작물에 심각한 피해를 유발하지만, 피해가 주로 지하부에서 진행되어 조기 진단이 어렵다. 본 연구는 강원도 주요 재배지의 약용작물인 잔대(Adenophora triphylla)와 어수리(Heracleum moellendorffii)에 감염된 뿌리혹선충을 동정하고, 영상 기반 식생지수를 활용한 비파괴 진단 가능성과 기주 반응에 따른 생화학적 방어 기작을 규명하고자 수행되었다.
현장 조사 결과, 두 재배지에서 검출된 우점종은 당근뿌리혹선충(Meloidogyne hapla)으로 확인되었다. 접종 실험에서 잔대는 M. hapla 감염 시 심각한 위조와 생체중 감소를 보인 반면, 어수리는 높은 선충 증식에도 불구하고 제한적인 생육 피해를 나타내는 내성 반응을 보였으며, M. incognita 감염 후에는 회복 양상을 나타냈다.
NDRE는 기존 NDVI 및 VARI에 비해 생육 단계 변화와 포화 효과의 영향을 덜 받아 선충 스트레스를 안정적으로 반영하였으며, SPAD 값과 높은 상관성을 보여 생리적 회복 추세를 효과적으로 설명하였다. 또한, 잎 단위 분석보다 화분 단위의 연속 모니터링이 누적된 생육 피해를 평가하는 데 더 적합한 것으로 나타났다.
접종 밀도 실험에서는 선충 피해가 중간 밀도(1,000 eggs) 이상에서 정체되는 포화 효과를 보였다. 생화학적 분석 결과, 감수성인 잔대에서는 총 플라보노이드 함량(TFC)이 감소한 반면, 내성인 어수리에서는 M. hapla 감염 시 TFC가 대조구 대비 약 9–10배 증가하여 플라보노이드 유도가 주요 내성 기작임을 시사하였다.
이러한 결과는 영상 기반 식생지수 분석과 접종 밀도에 따른 피해 반응, 생화학적 분석을 종합할 때, 약용작물에서 뿌리혹선충 피해를 비파괴적으로 진단하고 기주 특이적인 피해 반응과 내성 기작을 해석할 수 있는 통합적 진단 틀을 제시한다.

목차 (Table of Contents)

• 1. Introduction 1
• 2. Materials and Methods 4
• 2.1. Experiment 1: Monitoring of Root-knot Nematode Infection, Reproduction, and Growth Responses in A. triphylla and H. moellendorffii 4
• 2.1.1. Sampling of Medicinal Plants and Soil 4
• 2.1.2. Isolation of Nematodes from Medicinal Plants 5
• 2.1.3. Morphological Identification 6
• 2.1.4. Molecular Identification and Phylogenetic Analysis 6
• 2.1.5. Plant Materials and Experimental Design 7
• 2.1.6. Transplantation and Nematode Inoculation 7
• 2.1.7. Growth Monitoring and Leaf Area Analysis 8
• 2.1.8. Isolate Nematodes from Medicinal Plants 9
• 2.1.9. Nematode Population Density 9
• 2.2. Experiment 2: Image-Based Vegetation Index Analysis for Evaluating Root-knot Nematode Infection Responses 10
• 2.2.1. Plant Materials and Experimental Design 10
• 2.2.2. Image Acquisition and Preprocessing 14
• 2.2.3. Establishment of Brightness Reference and Spectral Normalization 16
• 2.2.4. Calculation of Vegetation Indices 23
• 2.2.5. Chlorophyll Content Measurement 26
• 2.2.6. Measurement of Plant Growth and Nematode Infection 26
• 2.2.7. Growth Monitoring and Leaf Area Analysis 27
• 2.3. Experiment 3: Correlation of Physiological and Metabolic Responses with Spectral Indices in Medicinal Crops under Density-specific Root-knot Nematode Infection 28
• 2.3.1. Experimental Design and Nematode Inoculation 28
• 2.3.2. Image Acquisition and Vegetation Index Calculation 29
• 2.3.3. Analysis of Root Physiological Response and Phytochemical Composition 30
• 2.3.4. Assessment of Plant Growth and Nematode Population 31
• 3. Results 32
• 3.1. Experiment 1: Monitoring of Root-knot Nematode Infection, Reproduction, and Growth Responses in A. triphylla and H. moellendorffii 32
• 3.1.1. Detection Rate of Root-knot Nematodes 32
• 3.1.2. Morphological Identification 32
• 3.1.3. Molecular Identification 35
• 3.1.4. Plant Growth and Leaf Area Analysis 37
• 3.1.5. Reproduction and Population Density of Root-knot Nematodes 39
• 3.2. Experiment 2: Image-Based Vegetation Index Analysis for Evaluating Root-knot Nematode Infection Responses 41
• 3.2.1. Comparative Analysis of Host Suitability and Biomass Loss under Nematode Infection 41
• 3.2.2. Image-based Analysis of Time-course Changes in Leaf Area 43
• 3.2.3. Spectral Response and Vegetation Indices 45
• 3.2.4 Time-Course Changes in Chlorophyll Content 53
• 3.3. Experiment 3: Correlation of Physiological and Metabolic Responses with Spectral Indices in Medicinal Crops under Density-specific Root-knot Nematode Infection 55
• 3.3.1. Impact of Inoculum Density on Plant Biomass and Nematode Reproduction 55
• 3.3.2. Spectral Response and Vegetation Indices 58
• 3.3.3. Secondary Metabolite Content and Antioxidant Activity 62
• 4. Discussion 68
• 4.1. Host Specificity and Contrast Plant Responses to Root-knot Nematode Infection 68
• 4.2. Applicability and Limitations of Image-Based Remote Sensing: Effects of Growth Stage and Sensor Resolution 69
• 4.3. Multi-Scale Diagnosis: Destructive Leaf Analysis vs. Continuous Canopy Monitoring 70
• 4.4. Limitations and Potential of Spectral Indices for Stress Diagnosis 71
• 4.5. Verification of Nematode-specific Growth Suppression and Vegetation Index 73
• 4.6. Density-dependent Growth Responses and Threshold Effects 74
• 4.7. Biochemical Defense Mechanisms: Roles of Secondary Metabolites and Limitations at Juvenile Stage 75
• 5. Conclusion 77
• 6. References 78