胡瓜苗期耐熱篩選指標之研究

在這日益暖化環境下，胡瓜 (Cucumis satives L.)在夏季的生產遭遇高溫已呈常態，因此解決高溫對胡瓜生產之影響，除了選擇適當的栽培措施外，選育耐熱品種為主要育種目標。在育種工作中，若能利用苗期進行篩選，且建立與田間產量結果對應之模式，可減輕後代繁瑣的育種選拔之工作量。本論文利用KS no. 3 (高雄3號)、Wen nong 210和CU-127等小胡瓜品種為材料，探討不同溫度及培植方式之苗期耐熱性狀變異篩選，並進行不同高溫處理苗期後其農藝性狀、生理及抗氧化酵素的變化及高溫下根系之反應，期能建立穩定及有效的胡瓜苗期耐熱篩選指標。不同苗期培植篩選方法試驗，組培瓶苗變方差值大於穴盤苗，顯示瓶苗有較大變異量，在進行溫度處理時反應較為靈敏，而穴盤苗的整齊度相對優於組培瓶苗，在考量時間及試驗材料之整齊度上，選擇以穴盤苗作為篩選方式。熱逆境下三個品種的一本葉幼苗進行在不同高溫處理下農藝性狀及根部性狀之分析結果，胡瓜幼苗經高溫處理 (28,35,38,43及45℃)於三個胡瓜品種KS no. 3，Wen nong 210和CU-127調查苗期植株性狀及根系發展表現的結果，發現葉綠素計讀值、幼苗之葉長、葉寬、葉重、地上部鮮重、乾重及地下部根乾重等性狀在胡瓜幼苗期對溫度敏感，且除葉綠計讀值外，各性狀之平均值在43℃及45℃均有明顯下降，顯示43℃為小胡瓜幼苗期高溫逆境之反應溫度。在地下部性狀，KS no. 3在根長、和根乾重之平均值優於其他二個品種，在開花期根系分布密度調查中，KS no. 3根系分布密度在土下40cm、50cm和總數上明顯優於其他兩個品種，且高溫期根之伸長及分佈的量與產量存在顯著正相關，此結果亦顯示根系分布密度可為耐熱篩選指標之一。在生理及抗氧化酵素變化之試驗中，CU-127品種之細胞膜對熱穩定性高於KS no. 3品種，在45℃臨界溫度時，CU-127 品種之F0值與Fv/Fm值均顯著高於KS no. 3 品種，顯示胡瓜的幼苗在高溫下細胞膜的穩定性越高時耐熱性越佳。再以生理指標 (葉綠素含量、H2O2含量與MDA含量)及抗氧化酵素活性 (CAT)與滲透調節物質 (脯胺酸)為測試參數，在抗氧化酵素分析試驗中KS no. 3品種在28-43℃處理時，H2O2含量均高於其他品種，因此推測Wen none 210與CU-127兩品種在高溫逆境下，藉由提高APX活性而降低H2O2含量，增加細胞膜的穩定性，進而減緩葉綠素降解。三種胡瓜品種脯胺酸含量會隨著處理溫度提高而有逐漸增加的趨勢，顯示胡瓜在高溫下會同時提高抗氧化酵素CAT活性與脯胺酸含量保護細胞膜的穩定性，以上這些參數在各試驗溫度間均達極顯著差異且表現趨勢一致，CV值均在10%以下具穩定性。綜合試驗之結果，胡瓜幼苗高溫臨界溫度為45℃，及葉綠素含量、H2O2含量及MDA含量等生理指標之變化可視為重要之耐熱指標。因此，若進行胡瓜苗期篩選時，在高溫環境下葉綠素降解緩慢、H2O2和MDA含量低，且具有強勢的根系之品系，即是選拔之目標。

關鍵字

胡瓜；耐熱；根系；抗氧化酵素；生理指標

並列摘要

When the temperature exceeds 35°C, cucumbers (Cucumis sativus L.) are subjected to physiological disorders that affect the growing of male and female flowers and the shape of fruits, thus reducing crop quality. To mitigate the effects of high temperature on growth of cucumber, in addition to adopting appropriate cultivation measures, selecting suitable varieties is crucial for plant breeding. Successful screening during the seedling stage can reduce the burden of the complex offspring selection process. In this study, seedlings of three cucumber varieties Wen nong 210, CU-127, and KS no. 3 were treated with different temperatures (i.e. 28°C, 35°C, 43°C, and 48°C) under different selection methods. After, selectee a more suitable screen method changes in their growth and root performance, physiological traits and antioxidant enzyme activities were analyzed to provide a reference for screening heat-tolerant varieties. In different temperature and culture mode, the mean square of vitro cultural seedlings was larger than the plug seedlings, indicating the reaction was more sensitive when the different temperature was processed. But the plug seedling method was chosen due to the uniform of the plant and the efficiency on the growth. Under heat stresses temperature, three cucumber varieties (KS no. 3, Wen nong 210 and CU-127) were grown under different high temperatures (28, 35, 38, 43 and 45℃) to test their growth and root performance. The experiment observed the seedling traits after high temperature treatment, show SPAD value, leaf length, leaf width, leaf weight, shoot weight, dry weight and root dry weight responses were significantly different among different temperatures. And except for the SPAD value, the mean of each trait is significantly reduced at 43 ° C and 45 ° C which indicating that 43 ° C is the threshold temperature for high temperature stress in the vegetative state of cucumber. The root length and root dry weight of KS no. 3 seedling were higher than the other three varieties. Particularly, the root distribution at 40 cm, 50 cm below the soil and their total number of KS no.3 were significantly higher than other two varieties during the flowering stage. Significant positive correlations founded on the root elongation and different depth distribution of roots and yield in the high temperature period. This result also indicating that root desity can be a selection index for heat tolerance. The experiment of changes in physiology and antioxidant enzymes, showed that the thermal stability of the cell membrane of CU-127 was more favorable than that of KS no. 3, simultaneously, Furthermore, at the critical temperature of 45°C, the F0 and Fv/Fm values of CU-127 were substantially higher than those of KS no. 3, indicating that for cucumbers, a high membrane stability under high temperature equates to a superior heat tolerance. Subsequently, physiological indices (i.e., the contents of chlorophyll, H2O2, and MDA), the activities of antioxidant enzyme of CAT, and osmosis regulatory substance (i.e., proline) were adopted as testing parameters. When treated at 28–43°C, KS no. 3 exhibited higher H2O2 content than its counterparts. This Speculated that under high temperature stress, Wen none 210 and CU-127 increased their APX activity to reduce H2O2 content so as to increase membrane stability, which subsequently slowed down chlorophyll degradation. Increasing the treatment temperature caused the proline content in the three cucumber verities gradually increased; indicating that cucumbers both increase the activity of antioxidant CAT and proline content to maintain membrane stability under high temperatures. And, their CV values were all under 10%, showing that during the heat tolerance screening they responded stably to different temperature treatment. As a result of the comprehensive test, 45°C is the heat threshold for cucumbers during the vegetative state. Thus, this heat tolerance screening method can be recommended to use in seedling stage which choose the first leaf stage of plug seedling as a screening method under high temperature stress which root traits, changes in H2O2, MDA, and chlorophyll content can be used as physiological indicators of the heat tolerance of cucumbers for seedling heat tolerance selection. Therefore, if the cucumber seedling screening was carried out, the line selected will possess with slowly chlorophyll degradation, lower H2O2 and MDA content, and strong root system in the high temperature.