催花後不同發育階段低溫處理對 ‘台農十七號’鳳梨植株及果實發育之影響

Abstract

In order to produce pineapple fruits year round in Taiwan, pineapple growers usually forced flowering in the late fall or winter to force the production of pineapple fruits by late spring or summer. The purpose of this study was to investigate the effects of low temperature upon the development of the ‘TN-17’ pineapple plants and fruits, during different time periods after forced flowering. The ‘TN-17’ pineapple plants underwent an application of forced flowering. Next they were exposed to 12℃/8H, 3℃/16H for 3-5 day periods during different stages of their development, then the they allowed to grow to maturity. At the end of 50 days, photosynthesis, stoma conduction, and Net CO2 exchange were found to be very low, but throughout the experiment, during the dark to light period, they showed a peak. On the 6th、12thand 17th days after forced flowering, chlorophyll fluorescence parameter Fo value also showed a peak. However, in browning areas caused by chill injury, Fv/Fm, Fv/Fo, chlorophyll fluorescence parameter and chlorophyll content decreased to almost 0. Additionally, the green part of leaves suffered high membrane leakage. The components of photosynthesis that were measured after cold exposure at 3℃, were titratable acid, total soluble sugar, and starch. Titratable acid was increased. Total soluble sugar in the green part of leaves decreased while in the shoot apex and the white part of the pineapple plant there was no change. On the other hand, total soluble sugar increased in the white part but decreased in the shoot apex. As for starch content, there were no significant differences between the control and low tem perperature treatment, but the total trend in the shoot apex was that the starch content rose. Ethylene production, respiration rate, and mineral content were affected by low temperature treatment. Ethylene production and respiration rate showed no significant differences in the control, the white part, and the shoot apex, but increased slightly in the green part. However, the total trend of ethylene production and respiration rate was a decrease in the shoot apex. Minerals showed a decrease of K in the white and green part; an increase of Mg in the white part；a decrease in total carbon content and C/N; and no significant differences in all other minerals. Further results in mineral analysis were in the comparison of flowering and non-flowering plants. C、N、Ca and Mn were higher in flowering than in non-flowering. K and Fe was lower in flowering than non-flowering. Minerals in the white portion of flowering plants were lower than non-flowering except for Mn. C、Ca and Mn in the shoot apex of flowering plant were higher than non-flowering, but P、Fe、Zn and Cu were lower than the non-flowering. After low temperature treatment, there was no apparent physical injury to the shoot apex, but injury symptoms did show up in the resulting leaves and fruits. Those plants that were exposed to low temperature between 0-6th day after forced flowering showed the lowest flowering rate. The resulting number of fruitlets and fruit weight were also lower than at any other stages. Exposure to cold during the inflorescent stage damaged the young plants but resulted in higher cold tolerance in the maturing plants and fruits. However, there was some phellem-like growth on the skin of the fruit. After low temperature treatment, the color turning rate of the peel and pulp were slowly than the control. The total soluble sugar and starch was also lower, Zn content was lower, but the Mn content was higher. There were no significant differences in other minerals. In conclusion, forced flowering and low temperature treatments resulted in the following: browning spots on the green part of leaves, decreased flowering rate, increased titratable acid, decreased total soluble sugar, and plant death in cases of serious cold injury. Low temperature had a serious affect on fruit weight, fruit appearance, and fruit quality.