지황(Rehmannia glutinosa Libosch.)의 2기작 재배 기술 개발, 연작장해 경감을 위한 토양 훈증처리 및 관련 균주 동정 = Development of Double Cropping Cultivation Techniques of Rehmannia glutinosa Libosch., Reduction of Replant Failure via Soil Fumigation and Identification of Related Fungal Strains

다국어 초록 (Multilingual Abstract)

Rehmannia glutinosa, a perennial rhizomatous herb, belongs to the Scrophulariaceae family and is one of representative medicinal plants widely used in the East Asian countries including Korea and China. A single cropping is common for R. glutinosa in Korea when rhizome propagules are planted in early May and harvested in early November. This practice usually leads to an oversupply of marketable rhizomes but a shortage of propagules for planting in the following year, which requires a development of other cropping system such as double cropping to solve this problem. For the double cropping system, the determination of planting time and planting spacing is necessary to maximize yield. This crop is known to be vulnerable to a replant failure caused by a successive cropping, which requires a development of reliable methods to alleviate this replant failure problem. Moreover, identifying the fungal species involved in the replant failure of R. glutinosa is prerequisite for controlling the pathogenic damage associated with the successive cropping. This study consists of three main chapters using R. glutinosa ‘Togang’ as an experimental plant. Chapter 1 determined the effect of planting time and planting spacing for a double cropping system on the growth, rhizome yield and a bioactive compound catalpol content. In the Chapter 2, the effect of soil moisture status on growth, photosynthesis, chlorophyll fluorescence, antioxidant enzyme activity, and bioactive compound content was investigated. Chapter 3 examined how rhizome residues left in the field after harvest influence growth, root rot incidence and yield. In addition, a chemical soil fumigation was tested in an effort to alleviate the replant failure problem, and fungal species that are responsible for root rot disease were identified.
To conduct the planting time experiment in the Chapter 1, rhizome propagules for the ‘first crop’ in a double cropping system have begun to be planted from 16 March, four times at 10-day intervals at the spacing of 30 cm × 15 cm, and harvested in late July. For the ‘second crop’, propagules have begun to be planted from 30 July, three times at 10-day intervals at the same spacing, and harvested in early November. For the planting distance experiment, propagules were planted at the spacing of 10 cm × 15 cm, 10 cm × 20 cm, 15 cm × 20 cm or 30 cm × 15 cm on 7 March and 30 July for the first crop and second crop, respectively, and harvesting was done at similar times to the first experiment for each crop. Rhizome yield increased with increasing growing periods in each crop. That is, the earliest planting in the first crop (16 March) produced 1,206 kg/10a, while the earliest planting in the second crop (30 July) yielded 1,107 kg/10a. The most effective planting spacing for yield was found to be 10 cm × 20 cm in both crops, showing an increase of about 40% compared to the 30 cm × 15 cm spacing.
In the Chapter 2 experiment, potted ‘Togang’ plants were irrigated according to five different soil water statuses, -10, -20, -30, -40 or -50 kPa, with each moisture level being controlled using tensiometers throughout the experiment. The effects on sprouting rate of rhizome propagules, vegetative growth, rhizome yield, photosynthetic characteristics, antioxidant enzyme activity, and rhizome catalpol content were measured. A significant reduction in the sprouting rate of propagules and vegetative growth (leaf number and growth) was observed at -50 kPa of the driest soil water status. Yield components such as rhizome number and the total and marketable rhizome weights were highest at the -30 kPa treatment. Root rot decay was highest at –10 kPa of the highest soil moisture (7.6% of total rhizome weight). Superoxide dismutase, peroxidase, and catalase activities were increased when the plants were exposed to water excess (-10 kPa) or water deficit conditions (-50 kPa). Net photosynthesis and transpiration rates were considerably higher at -20 kPa and -30 kPa than other treatments. Chlorophyll fluorescence measurements showed that the -20 kPa and -30 kPa treatments showed a maximum quantum yield (Fv/Fm) of higher than 0.8 (considered as stress threshold), whereas -10 kPa or -50 kPa treatments showed a reduction in the quantum yield of less than 0.8.
In the Chapter 3 experiment, two types of rhizome residues, healthy and diseased, were incorporated as a powder form into 200 L of fresh soil at 400, 800 and 1,600 g. To evaluate the effectiveness of soil fumigation in the soil where ‘Togang’ plants had once been cultivated, soil was fumigated with dazomet at 0, 30, 40 and 50 kg per 10 a before planting. To identify the fungal strains responsible for root rot, total eight strains were isolated from the diseased part of rhizomes, with each strain being identified using a molecular analysis of translation elongation factor 1 alpha (TEF1-α) and RNA polymerase Ⅱ subunit (RPB2) genes. Rhizome yield was considerably decreased by about 63% when diseased residues were added at the rate of 1,600 g per 200 L soil compared to the fresh soil control, whereas healthy residues had no effect. Soil fumigation with dazomet was able to effectively increase shoot growth and rhizome yield but decrease root rot in ‘Togang’ plants under successive cropping. The recommended application rate was found to be 40 kg per 10 a, where yield was substantially increased by about 61%. As for identification of the fungal species responsible for wilt and root rot, it was found that Fusarium sp_A strain was highly pathogenic and its sequences via TEF1-α and RPB2 analyses corresponded to those of the reference Fusarium solani strains in NCBI GenBank.
In conclusion, for the double cropping system of R. glutinosa ‘Togang’, the optimal planting time for the first crop is between mid- and late-March for harvesting in late July at the planting spacing of 10 cm × 20 cm, and the second cropping should be followed by immediately after harvest of the first crop to maximize yield. A suitable water management for R. glutinosa ‘Togang’ was achieved at about -30 kPa of soil moisture status. Soil fumigation with dazomet was quite effective in alleviating the negative effect of successive cropping on shoot growth, yield and root rot, especially when applied at the rate of 40 kg/10a. Dominant fungal species that are responsible for root rot in R. glutinosa ‘Togang’ was found to be Fusarium solani.

목차 (Table of Contents)

• Ⅰ. 서 언 1
• Ⅱ. 연구사 4
• Ⅲ. 연구결과 및 고찰 21
• 제 1 장. 지황 '토강'의 2기작 재배 시 재식시기와 재식거리에 따른 생육, 수량 구성요소 및 생장해석 22
• 1.1. Abstract 23
• 1.2. 서 언 25
• 1.3. 재료 및 방법 27
• 1.4. 결과 및 고찰 34
• 1.5. 적 요 76
• 제 2 장. 토양수분함량이 지황 '토강'의 생육, 광합성 및 항산화효소 활성에 미치는 영향 78
• 2.1. Abstract 79
• 2.2. 서 언 81
• 2.3. 재료 및 방법 84
• 2.4. 결과 및 고찰 92
• 2.5. 적 요 110
• 제 3 장. 지황 '토강'의 연작 시 근경 잔사물과 토양 훈증처리가 생장, 뿌리썩음병 및 수확에 미치는 영향과 뿌리썩음병 관련 진균 종의 구명 111
• 3.1. Abstract 112
• 3.2. 서 언 115
• 3.3. 재료 및 방법 118
• 3.4. 결과 및 고찰 122
• 3.5. 적 요 154
• Ⅳ. 종합고찰 155
• Ⅴ. 인용문헌 162
• Ⅵ. 국문초록 192