Effects of Extended Day Illumination on the Seedling Growth of Watermelon and Cucumber

本試驗研究係在位於臺中市霧峰區之行政院農業委員會農業試驗所農場進行，以三種瓜類作物(西瓜-‘新蘭’、’甜美人’，胡瓜-‘夏之輝’)為試驗材料，分別於日出前2 h 及日落後2 h 光照處理苗株4 h 以延長明期，據以探討特定光輻射延長明期光照對西瓜及胡瓜苗株生長之影響。人工光源包括發光二極體(LED; light-emitting diode)(計有730、660、590、520、500、470 及405 nm 等6 種特定波長)和省電燈泡(110-120V、23W、6500K 之Philips Helix 晝光色)，並以不照光為對照，合計8 種光源。種子於發根達1 cm 後移植穴盤生長(計有03/16/2010 及04/15/2010 兩栽植期)，分別於出土後14 d 及定植前調查苗株生長性狀，又分別於定植後7 d 及14 d 再調查幼株生長情形。由變方分析(ANOVA)發現，三種瓜類作物之兩栽植期各性狀皆無顯著性差異後，即將兩批資料予以合併分析。根據分析結果，胡瓜在出土後14 d 及定植前之株高、下胚軸長度、下胚軸乾重等在處理間存有差異，顯示苗株生長對延長明期光照產生反應，惟不同光源會造成不等生長差異。胡瓜苗株定植田間後7 d 之株高與下胚軸長度在處理間亦有差異，定植後14 d 時僅下胚軸長度存在差異，顯見苗期生長受到延長明期光照之效應可能延續至田間株幼初期生長，尤以對下胚軸伸長的影響最大。若將730 nm 的數據去除，再以變方分析探究處理間之差異，不同LED 光源間的差異不大，以藍光(470 nm)和紫光(405 nm)的株高、下胚軸長度和下胚軸乾重較對照組(不照光) 佳，顯示兩種光源有促進苗株生長的現象。西瓜‘新蘭’係於出土後14 d 時之株高和下胚軸長度在處理間存在差異，定植前只有下胚軸長度維持差異存在，定植後則無處理之間差異。若將730 nm 的數據去除，則在定植前的下胚軸長度在處理間有明顯差異，以綠光520 nm 的促進生長的效果最佳，此現象維持至定植後7 d，可知延長明期光照之效應僅及於苗期且以下胚軸具較強反應。西瓜’甜美人’的結果近似於’新蘭’，但是對下胚軸長度之效應可延至定植後7 d，同樣將730 nm 的數據去除，亦是在定植前的下胚軸長度在處理間有明顯差異，以綠光520 nm 和紫光405 nm兩種光源有促進生長的效果，此優勢生長也維持到定植後7 d。經檢視下胚軸長度與株高之關係，無論苗期或幼株生長初期大致呈現直線正相關，惟胡瓜可長達定植後14 d，可見延長明期光照對下胚軸伸長的促進可以反應在株高。在植株地上部鮮重與株高之關係上，三種瓜類作物概為直線正相關，尤其胡瓜在出土後14 d 即有此現象，顯示地上部鮮重隨著植株高度的增高而增加。 Field experiments were conducted in the experimental farm of Taiwan Agricultural Research Institute to study the effects of extended day illumination (4 h, i.e., 2 h before dawn and 2 h after sunset) on the seedling growth of watermelon (Citrullus vulgaris Schrad. ex Eckkl. & Zeyh) and cucumber (Cucumis sativus Linn) before and after transplanting. Artificial light sources were adopted to provide additional lighting, including light-emitting diodes (LEDs,) at 730, 660, 590, 520, 500, 470 and 405 nm and light bulb (LB) (110-120V, 23W, 6500K; Philips Helix white color) with no light treatment (CK) in comparison. Seeds of watermelon and cucumber were planted twice in cropping season of 2010. Samplings were made at fourteen days after seedling emergence (14 DAE), day before transplanting (BTP), 7 days after transplanting (7 DATP), and 14 days after transplanting (14 DATP). Based on results of analysis of variance (ANOVA), experimental data from both plantings were pooled for further study hereafter. There were significant differences in growth traits between light treatments of cucumber, including plant height (PH), hypocotyls length (HL), and hypocotyl dry weight (HDW) at 14 DAE and BTP, while significant difference of PH and HL was found at 7 DATP and only HL at 14 DATP. Variations existed among treatments of different light sources. By excluding data of 730 nm, there was no significant difference between light treatments. However, the increments of PH, HL and HDW by 470 nm and 405 nm were better than those of CK.Significant differences of PH and HL between treated seedlings were found in variety ‘Hsin-Lan’ of watermelon at 14 DAE, only HL at BTP, and no different after transplanting. By excluding data of 730 nm, there was a difference in HL at BTP, and 520 nm-treated seedlings had better growth than others till 7 DATP. The results of variety ‘Tien-Mei-Zen’ of watermelon were similar to those of ‘Hsin-Lan’, but lighting effect on HL extended to 7 DATP. Without data of 730 nm, difference between light treatments was found only in HL at BTP, especially at 520 nm and 405 nm. The relationship between PH and HL was linearly correlated in a positive fashion, and could extend to 14 DATP for cucumber. PH and aboveground plant fresh weight of treated plants was also positively correlated linearly in the examined varieties of cucumber and watermelon. Such relationship appeared at 14 DAE for cucumber