การเปลี่ยนแปลงลักษณะสัณฐานสรีรวิทยาของใบต่อปริมาณสารพฤกษเคมี ในใบพืชกระท่อม (Mitragyna speciosa (Korth.) Havil.)

Abstract

The national master plan for developing Thai herbs policy promotes using local medicinal plants that have potential benefits. Recently, Kratom leaf (Mitragyna speciosa) was listed as a legal herb and has become one of the most demanded herbs in the Thai local medicinal and consumer market. Thus, in order to supply the market demand with high quality, phytochemical constituents in the leaves need to be consistent with the quality standards. This study aimed to compare the growth development stage and phytochemical constituents in the leaves under different fertilizer applications. The first experiment was conducted with four different chemical fertilization (N-P-K) rates: nil fertilization (N0) (control); 15-15-15 (N15); 21-0-0 (N21); 15-15-15 plus foliar fertilizer (N15+15). It was found that the fertilizer application of N15+15 resulted in increased leaf weight, leaf area, plant height, stem diameter, and canopy width, enhancing the photosynthetic rate. For the mitraginine changes, it was found that development of the third leaf pair the highest mitraginine content of 4.54 %w/w. The biomass accumulation in plant parts of Kratom were not different. All parts of the plant were accumulated in similar amounts in all treatments. Nutrient accumulation in the leaves was significantly different in the different fertilization rates. In all three stages of leaf development, N15 fertilization had high nitrogen and potassium accumulations, while fertilizing N15+15 had an increased accumulation of phosphorus in the third and fifth leaf pair stages. On the other hand, the control treatment (N0) and N21 resulted in the accumulation of calcium by plants and the highest magnesium in all three developmental stages of Kratom. The experimental results approved that appropriate fertilizer application was vital to enhance leaf growth, leaf production, and phytochemical contents in the fresh leaves of Kratom plants. After harvesting the kratom leaves, they tend to deteriorate rapidly during storage. Thus, with an objective to address the issue, the second experiment was to the effects of storage temperature and chitosan coating on the Kratom leaves during their shelf-life. The experiment set two different temperatures: (15 and 25 °C), for the storage of the Kratom leaves, which were coated with varying concentrations of chitosan: 0.0, 0.5, 1.0, 1.5, and 2.0%. It was found that the low temperature could extend the shelf life of the chitosan-coated Kratom leaves. The leaf coated with chitosan 0.5% showed less percentage of weight loss under the storage temperature of 15 °C than that of 25 °C. Both storage temperatures did not affect the changes in the Kratom shelf-life leaf color (a*, b*, and L*). However, the chlorophyll contents of leaves stored at 15 °C (22.87-32.5 mg/cm2 ) were higher than at 25 °C (20.05-26.57 mg/cm2 ). The experiment found that storing the chitosan-coated leaf at a low temperature could extend the shelf life of Kratom leaves by 15 days. The research findings would contribute to formulating the crop management guideline for Kratom plants. The phytochemical contents in the leaves varied with the plants’ fertility, crop management, and the growing area environment. However, further studies are needed on the packaging and leaf active substances to ensure efficient storage for the Kratom leaves.