南瓜砧木幼苗耐寒性及其低溫下生理表現之分析

Analysis of Chilling Tolerance and the Physiological Performance of Squash Rootstocks under Low Temperature

農民常使用嫁接苗以提升田間瓜類植株的生長勢，其中南瓜為常用砧木種類。瓜類嫁接苗於冬季及早春容易遇到低溫，因此需有耐低溫之南瓜砧木品種，降低種苗於低溫逆境下不良的生理生化反應。本研究蒐集市售南瓜砧木品種、農業改良場或種苗業者提供之品種(系)於低溫(10/8°C)處理六天的條件下，收集不同生理指標數據藉以綜合評估十品種(系)南瓜砧木幼苗之耐寒性。低溫處理後品種(系)間葉片出現不同程度的寒害病徵，‘鐵甲’、‘春力’的葉片維持翠綠，‘壯士’及Si2FC品系的葉片出現明顯壞疽。低溫後各品種(系)葉片PSII最大光化學效率(Fv/Fm)皆下降，丙二醛含量及電解質滲漏率上升。植株經過低溫(10/8°C)六天回至室溫(25°C)兩天後，‘壯士’、Si1si2及Si2FC品系的Fv/Fm未回升。進一步將四個生理指標包含低溫後、回溫後的Fv/Fm比率、丙二醛含量比率及電解質滲漏率比率計算成隸數函數及綜合指標值進行綜合評估。依綜合指標值篩選結果顯示‘鐵甲’、‘春力’及5254具有高度耐寒性，寒害指數與綜合指標值的Pearson相關係數為0.82。

Farmers often use grafted cucurbit seedlings to improve plant growth vigor in the field and Cucurbita spp. are commonly used rootstocks. The grafted cucurbit seedlings are usually subjected to low temperature stress in winter and early spring. Therefore, chilling-tolerant Cucurbita rootstock cultivars are needed to reduce the adverse impacts of low temperature on physiological and biochemical processes of the cucurbits. In this study, we collected ten Cucurbita rootstock cultivars (strains) and evaluated their chilling tolerance under low temperature 10/8°C for 6 days based on plant physiological indices. After low temperature 10/8°C for 6 days, the leaves showed different levels of chilling damage, with‘Tiejia’and‘Chunli’remaining green, whereas‘Zhuangshi’and Si2FC exhibiting obvious leaf necrosis. The maximum photochemical efficiency of PSII (Fv/Fm) values were reduced, and both the malondialdehyde (MDA) content and electrolyte leakage (EC) were increased for all cultivars (strains) under 10/8°C for 6 days. Among tested cultivars (strains),‘Zhuangshi’, Si1si2 and Si2FC didn’t resume their Fv/Fm values after subsequent recovery at room temperature 25°C for 2 days. The four physiological indicators including Fv/Fm ratio after chilling and after recovery, ratios of MDA content and ratios of EC after chilling were further calculated into the membership function and comprehensive index value for assessment. According to the comprehensive index,‘Tiejia’,‘Chunli’and strain 5254 had high chilling tolerance and the Pearson correlation coefficient between chilling injury index and comprehensive index was 0.82.