제주 자생 상동나무의 특성과 생장조정제 처리가 열매 품질에 미치는 영향

Abstract

Sageretia thea (Osbeck) M.C. Johnst is found to have been intensively distributed in Jeju island. In order to discover the possibilities of the tree as a new income-source crop or functional food material, this research was made by selecting the naturally growing habitat located in Seogwipo-si Anduk-myeon Seogwang-ri to identify its locational environment properties, vegetation distribution and soil properties of the habitat, and to investigate morphological and growth characteristics and physicochemical features of the fruit in a functional component analysis. In addition, the effects of seed germination characteristics and growth regulator treatments on the quality of the fruit are throughly investigated in this study to prepare a utilization basis for a functional resource of the fruit and to further create a new demand. The results of this study are as follows:

1. In Korea, Sageretia thea is mainly distributed and naturally growing in the warmer southern regions of Jeollanam-do and south coastal islets and all over the Jeju Island. In particular, the trees are intensively growing in the middle of mountain areas in the western part of Jeju island. The vertical limit of biological distribution zone is known to be less than 600m above sea level. The climatic and environmental conditions of Sageretia thea habitat belong to the evergreen broadleaf forest region, and the trees tend to grow well in a place which has a small amount of precipitation and a high degree of temperature in winter. Soil characteristics of the habitat are as follows: 5.8 of pH, 0.34dS·m-1 of EC, 15.27% of organic matter, 13.6mg·kg-1 of available P2O5, exchangeable cations including 4.9 of Ca, 0.27 of K, 1.7 of Mg, 1.3cmolc·kg-1 of Na and 63.09mg·kg-1 of NO3- ions, respectively. When those distributional characteristics, climatic and environmental conditions and soil properties of the naturally growing habitat described above are taken into a cultivation perspective, the Sageretia thea is determined suitable for cultivation and promising for a new income agricultural crop. In addition, the flora of the habitat comprises the total of 31 classification groups including 25 families, 31 genuses, 27 species, and 4 plant varieties, and 5 types of plants are distributed according to the classification of the vegetable kingdom designated by the Ministry of Environment.

2. The fruit of Sageretia thea collected from the habitat in harvest season has the average weight of 0.2g, diameter of 7.2mm, length of 6.5mm, and size distribution range of 5.1～10.0mm with 75.1% of 6.1～8.0mm in the most frequently checked size, revealing a special feature of the seeds, that is, the bigger fruits, the greater the number of seeds. The number of fruits per cluster was not significant in size or weight, but it was proportional to the number of seeds. The number of seeds per fruit was 1.8, and 1000 grain weight was 7.77g with diameter of 3.7mm and thickness of 1.7mm in size, light and small. The fruit maturation was investigated to be from April 27 to June 1, approximately 35 days, when the best maturation period was about a week, May 11 to May 18. Also, the fruits grown on May 4 to May 11 were seen to have the biggest in transverse size and weight with a tendency of the earlier maturation date the greater the number of seeds.

3. The physicochemical properties and functional components of Sageretia thea are found in the following analysis. The extracted fruit juice had 4.17 of pH, 22.2°Brix of soluble solid, 0.83% of total acidity and 26.7 of soluble solid-acid ratio. As a result, the high sugar content of the fruit was evaluated as excellent palatability, more appealing to consumers than other fruits. The proximate composition of fruit was 75.04% of moisture content, 18.31% of available nitrogen-free extract (carbohydrates), 3.32% of crude fiber, 2.01% of crude protein, 0.84% of crude fat, 0.48% of crude ash content, and the main components of the fruit was considered to be water soluble total sugar, mostly occupying available nitrogen-free liquid. The moisture content lower than other fruits is because of the higher level of water soluble sugar content. The freeze-drying sample of the fruit juice contained a total mineral content of 1,264.9mg·100g-1, main mineral components of K, P, Na, Mg and Ca, where 822.8mg·100g-1 of K was contained the most, and a tiny amount of other various mineral components, Fe, B and the like.

A variety of major organic acids of the fruit included malic acid, lactic acid, tartaric acid, succinic acid, citric acid in an orderly manner, revealing an organic acid composition different from other fruits, so that the fruit juice of Sageretia thea was considered to bring about a unique sensation of refreshment. Malic acid and lactic acid, respectively 2,631.54mg·100g-1 and 1,237.4mg·100g-1, were amounted for 73.2% of total organic acids. Free sugar content included fructose of 8.11g·100g-1 and glucose of 7.68g·100g-1 with only a small mixed amount of sucrose, and the main composition of the soluble solid and available nitrogen-free components mentioned above were confirmed as free sugar. It was confirmed that 11 fatty acids were contained in the fruit and some of major acids were palmitic acid, stearic acid, oleic acid and linoleic acid, the last of which was contained the greatest in amount. Besides, the fruit also contained γ-linolenic acid, eicosa trienoic acid, etc. rare in nature. It was also found that the saturated and unsaturated acids were 28.74% and 71.26% of the total fatty acids respectively. Total phenolic compound, known as a functional material, was contained in the amount of 874.8mg·100g-1, very rich in fruit, and the amount of anthocyanins, a typical functional component, was 520.8mg·100g-1, even more than blue berries, in the content analysis of anthocyanins, so that the fruit of Sageretia thea was considered to have a high value for a functional food material resource.

4. Sageretia thea seeds pretreated for 24 hours at 50℃ were not germinated, while most of those pretreated for 24 hours at 4℃ were successfully germinated at any degree of temperature (except at a temperature of 10℃). Particularly, the highest germination rate of 55% was made at 15℃, and shoots and radicles were best grown within the temperature range of 25℃. As temperature was higher, some tendencies were seen to get mean germination time shorter, the germination coefficient of velocity higher and the germination index lower. On the basis of germination rate and growth conditions, it was confirmed that seeds of Sageretia thea might be most preferably germinated at 20℃.

5. Some plant growth regulator treatments to the fruit cluster of Sageretia thea were conducted in a dipping method, and then the effects of those immersion treatments on the quality of the fruit were investigated. Firstly, 250mg·L-1 mepiquat chloride treatment or 1mg·L-1 thidiazuron treatment on the full-bloom date resulted in an increase of 21.7% in weight, and 1mg·L-1 thidiazuron teatment on the full-bloom date, 200mg·L-1 6-benzylaminopurine treatment on the full-bloom date and 10mg·L-1 forchlorfenuron treatment 14 days after the full-bloom date also brought about positive effects on the enlargement of the fruit, respectively, 8.1%, 7.0 % and 6.3 % in its transverse diameter.

Furthermore, the positive effects of the plant growth regulator treatments on the harvest time of Sageretia thea were determined as follows: an increase in the harvest ratio of 48.6～75.8%, shorter maturation period, by the treatments with 500mg·L-1 mepiquat chloride 7 days after the full-bloom date, 2.5mg·L-1 forchlorofenuron 14 days after the full-bloom date or 200mg·L-1 6-benzylaminopurine 7 days after the full-bloom date; and the greater effects of plant growth regulator treatments on the fruit maturation speed in the following order, gibberellic acid> thidiazuron> mepiquat chloride> forchlorfenuron> 6-benzylaminopurine.

As described above, a thorough research has been made on naturally growing habitat of Sageretia thea in Jeju. special features of fruit, characteristics of seed germination and effects of plant growth regulator treatments. The results of this study are expected to be used as a comprehensive reference base to develop Sageretia thea as a new local specialty crop for Jeju island