Effects of Dolomite Application on Plant Growth, Activities of Polyphenol Oxidase and Internal Quality of Grand Rapids Lettuce

摘要

The purpose of this experiment was to investigate the effect of preharvest soil application of dolomite on the growth, activity of Polyphenol oxidase (PPO) and internal characteristics was evaluated on lettuce cv. Grand Rapids under field conditions. A factorial in completely randomized design was arranged with four replications and composed of two factors; application time four levels (25, 40, 55 days after planting, DAP compared with untreated treatment, Control) with four concentration rates (0, 50, 100 and 150 ppm). The results show that dolomite application irrespective of application times or concentration rates had no effect on stem diameter, plant height, degree of leaf browning, fresh weight, biomass, chlorophyll content, leaf colour in terms of a* and b*, the content of phenolic, quinone, Total Soluble Solids (TSS), Titratable Acidity (TA), pH or ascorbic acid content. While maximum response of leaf increment was achieved with treating of 150 ppm dolomite at 25 DAP. Dolomite application irrespective of concentrations at all application times (25, 40 and 55 DAP) reduced the bush size compared with the control. In addition, application of 150 ppm dolomite at 55 DAP had the maximal brightness of leaf colour, L* value. Furthermore, dolomite treatment of 50 ppm at 25 DAP gave the least level of PPO activity at 33 DAP.