植體水分狀況及碳水化合物變化對洋桔梗切花品質之影響

Abstract

洋桔梗 [Eustoma grandiflorum (Raf.) Shinn.] 為臺灣極具潛力之外銷切花作物。切花採收前限制供水為目前慣行之操作技術，但實際效果不明確。本研究探討洋桔梗對既行限水模式之反應，及此等反應對切花品質之影響，並觀察切花瓶插期間水分及碳水化合物利用，期能提升洋桔梗栽培管理與採後處理技術。 當洋桔梗切花上留存之葉片數由0增加至6或12片，切花吸水速率上升，但葉蒸散速率亦增加，保留12片葉之切花提早失水萎凋。花蕾由成熟至開放期間鮮重增加為1.4倍，為主要利用水分之階段。花序頂端未成熟小蕾於瓶插期間並未開放，對觀賞品質及水分平衡皆無影響。不同品種洋桔梗小花間競爭關係不同，‘Bolero White’ 和 ‘Bolero Blue Flash’ 於花蕾開放同時，已開放之小花萎凋，但整體切花壽命較長。‘Arena Pink’ 和 ‘Ex Rosa Pink Flash’ 花蕾開放不影響已開小花之壽命，然至瓶插中後期吸水速率快速下降而使切花壽命提早結束。故 ‘Ex Rosa Pink Flash’ 切花壽命隨著已成熟花蕾數目增多而延長，摘除花蕾並不會延長已開小花之單朵壽命。 可見花蕾後給予洋桔梗限水處理，維持30%及40%以上介質水分含量者，植株生長量及含水量較高，但20%至25%介質水分含量處理促進 ‘Piccolo Lime Green’ 及 ‘Ex Rosa Green’ 切花水分累積及維持。於 ‘Piccolo Lime Green’ 觀察到氣孔隨介質水分降低而關閉，‘Ex Rosa Green’ 莖葉葡萄糖濃度受限水而提升。然二品種中僅有 ‘Piccolo Lime Green’ 因限水減緩小花萎凋而壽命延長。介質水分含量維持10%至15%造成植株生長明顯受抑而無法生產切花。 於田間限制給水， ‘Piccorosa Snow’ 品種因吸水速率降低導致切花壽命略微縮短，但切花若經過1小時採後離水，先前經採前限水處理之切花可於復水後有效恢復水分平衡，採前增加灌溉者之切花則因採後離水而壽命減短。 洋桔梗花朵中主要碳水化合物為葡萄糖，於瓶插前佔其乾重之7.8%，瓶插7日後則降低為乾重之3.5%。瓶插液所添加碳水化合物主要於瓶插7日內花蕾開放期間被切花吸收，累積於花朵與莖葉中。瓶插於20 g∙L-1葡萄糖或蔗糖可促進洋桔梗花蕾開放及切花鮮重維持。果糖亦可有效提升切花品質，但需配合8-羥基喹啉磺酸殺菌劑使用以達最佳效果。

Eustoma grandiflorum (Raf.) Shinn. is a cut flower crop with high economic potential in Taiwan. Before harvest, growers usually reduce irrigation, but there have been no studies on how this process affects cut flower quality in Eustoma. In this study we investigated the responses of Eustoma to preharvest water deficit and observed water and carbohydrate flow in cut flowers, to improve production and postharvest techniques. When 0, 6, or 12 leaves were kept on stem per cut flower, water uptake rate increased along with number of leaves. However, 12 leaves on a cut flower caused excess transpiration, shortening vase life. Bud opening was the highest water consuming stage, with fresh weight increased up to 1.4 times from mature-bud stage to opened-flower stage. Uppermost immature buds did not open during the period cut flowers were in vase and had no impact on visual quality or water balance of cut flowers. Differences in regard of competition between florets were observed between cultivars. ‘Bolero White’ and ‘Bolero Blue Flash’ florets wilted when younger buds on the same inflorescence opened, resulting in longer inflorescence life. By contrast, bud opening of ‘Arena Pink’ and ‘Ex Rosa Pink Flash’ made no impact on keeping time of opened flowers, their inflorescence life was shortened by a decline in water uptake after bud opening. Hence vase life of ‘Ex Rosa Pink Flash’ is lengthened by additional number of mature buds, the removal of unopened buds did not increase life of originally opened flowers. Maintaining medium water content above 30% or 40% after visible bud stage in Eustoma resulted in higher growth and plant water content. Keeping medium water content between 20% and 25% improved cut flower water balance in cultivars ‘Piccolo Lime Green’ and ‘Ex Rosa Green’. ‘Piccolo Lime Green’ had lower stomata conductance with lowered medium water content, while ‘Ex Rosa Green’ grown under 20% to 25% medium water conent had higher glucose concentration in leaves and stem. Yet cut flower vase life and floret life was lengthened by lower medium water content only in ‘Piccolo Lime Green’. Preharvest medium water content between 10% and 15% reduced growth of Eustoma such that harvestable quality was not reached. Differences between preharvest irrigation treatments on Eustoma were less pronounced when growing plants in field than in pots. Due to lower water uptake rate, cultivar ‘Piccorosa Snow’ had shorter vase life when grown in water deficit field plots. Nevertheless cut flowers showed better recovering of a positive water balance after an hour of postharvest water stress. Vase life of flowers grown with doubled (16 L∙m-2/wk) irrigation was shortened by postharvest water stress treatment. The most abundant soluble carbohydrate in Eustoma flowers is glucose, accounting for 7.8% flower dry weight. Glucose was consumed mainly during bud opening, after which glucose concentration dropped to 3.5%. Sugars originally supplied to vase solutions accumulated in flowers and vegetative parts during bud opening. Vase solution containing 20 g∙L-1 glucose or sucrose aided bud opening and fresh weight maintaining. Fructose in vase solution may also promote cut flower quality, especially when 8-hydroxyquinoline (8-HQS) is added.