不同開花熱延遲菊花品種之形態及生理研究

Abstract

菊花[Dendranthema ×grandiflorum (Ramat.) Kitamura]是世界重要花卉，其生長及開花受季節、溫度及光週等因子影響。高溫環境下會延遲花芽創始及發育，使菊花品種有不同程度開花延遲。本研究比較不同開花熱延遲之菊花品種，在高溫下之莖頂分生組織(shoot apical meristem, SAM)形態發生、花芽創始與發育、開花時間、葉片細胞膜穩定性與頂梢碳水化合物之變化，以更清楚開花熱延遲之機制。另探討應用激勃素減緩菊花開花熱延遲。 不論在秋冬季(11.5-13.5 h)及夏秋季(11.5-14.5 h)自然日長下以日/夜溫30/25、25/20及20/15℃處理，或在12 h光週下以30/25及20/15℃處理，菊花‘卡若里’之SAM直徑與發育階段、花下葉片數、花芽發育及開花時間於溫度處理間無顯著差異。而生長在30/25℃下，‘金風車’之SAM發育減慢，花下葉片數、花芽發育及開花時間都顯著增加。兩品種在不同環境下，若可達花芽創始階段，其莖頂分生組織之直徑皆為0.27-0.28 mm。兩品種在20/15℃下，以暗中斷4 h較12 h光週處理者延遲SAM與花芽之發育，而延後開花，尤以‘金風車’影響更大。在暗中斷、30/25℃處理120天後兩品種仍處於營養生長。 將兩品種於花芽創始後，移入日/夜溫(30/25及20/15℃)及光週期(12 h及暗中斷4 h)組合處理下，結果‘卡若里’在12 h光週下之花芽發育及開花時間於溫度處理間無顯著差異；與20/15℃處理比較，‘金風車’於30/25℃處理之花芽發育速率會減慢，到花日數增加36.2天。兩品種於暗中斷4 h、30/25℃處理下都形成柳芽，‘卡若里’之柳芽有1-2輪小花原體形成，但‘金風車’則柳芽無小花原體形成。 兩品種生長在11.5-12.5 h自然日長或於12 h光週、20/15℃環境下，於花芽創始後分別以30/25及20/15℃處理，調查葉片電解質滲漏並計算相對傷害值、丙二醛濃度、花芽發育期間淨光合作用速率與開花時間，結果‘卡若里’於30/25℃處理之葉片相對傷害值於處理24天後下降至42%-46%，處理12天後葉片丙二醛濃度無顯著增加，且花芽創始後之葉片淨光合作用速率、花芽發育及開花時間於溫度處理間無顯著差異。而‘金風車’於30/25℃處理24天後，葉片相對傷害值仍高達70%-80%，葉片丙二醛濃度在處理12天後逐漸增加，在花芽發育期間，30/25℃處理使葉片淨光合作用速率下降，並減慢花芽發育速率而開花延遲。 在12.5-13.5 h日長下分別以30/25及20/15℃處理，探討兩品種之莖頂分生組織發育與頂梢碳水化合物之關係，結果‘卡若里’在30/25及20/15℃處理與‘金風車’在20/15℃處理約第9天時花芽創始。兩品種在進入花芽創始期間，頂梢之蔗糖及總可溶性糖含量下降，而澱粉含量增加；當花序原體及小花原體形成時，頂梢之蔗糖、總可溶性糖及澱粉含量最高。而‘金風車’於30/25℃處理15天時花芽創始，但之後其頂梢之蔗糖、總可溶性糖與澱粉含量均低，花芽發育也較慢。 將兩品種移入12 h光週下分別以30/25及20/15℃處理，於10、12及27天取樣測量兩品種之SAM發育與不同節位葉片之乾重，結果顯示溫度處理並不影響‘卡若里’之各節位葉片乾重與SAM發育。‘金風車’於30/25℃高溫處理10及12天時，SAM發育速率較20/15℃處理者慢，且近頂端年輕葉片(1-10節)乾重顯著較高，顯示高溫有利於‘金風車’之年輕葉片生長，不利於莖頂行生殖生長。 於12 h光週、30/25℃環境下，‘金風車’於可見花苞時，以葉面噴施25及50 mg•L-1 GA3處理可縮短花苞顯色時間，提早開花約11天、並增加頂花苞直徑，降低葉及根之質量百分比(mass fraction percentage)，但增加花之質量百分比。在‘金風車’可見花苞後移至自然長日(14-14.5 h)、高溫(34.6℃)環境下，噴施50 mg•L-1 GA3會促進花梗長度、花苞直徑與花芽發育，可提早8天開花。

Chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] is one of the most important floriculture crops in the world. Season, temperature, and photoperiod affect growth and flowering of chrysanthemum. High temperature can delay flower initiation and flower development that led to different degrees of flowering-heat-delay in chrysanthemum cultivars. It is vital to have a better understanding of physiology and mechanism of flowering-heat-delay. This study investigated the effects of high temperature on shoot apical morphogenesis, flower development, time to flowering, leaf cell membrane thermostability, and shoot tip carbohydrate content in two chrysanthemum cultivars with different flowering-heat-delay sensitivity. Foliar spray of GA3 was tested to reduce possible flowering-heat-delay in chrysanthemum. Shoot apical meristem (SAM) diameter, developmental stage, leaf number below the inflorescence, flower development, and time to flowering did not differ in ‘Kaa Luoh-Lii’ among day/night temperature treatments (30/25, 25/20, and 20/15℃) under 11.5-13.5 h (autumn-winter), 11.5-14.5 h (summer-autumn) natural daylengths, or 12 h photoperiod conditions. In contrast, SAM development decreased, and leaf number below the inflorescence, flower development, and time to flowering increased as temperature increased from 20/15 to 30/25℃ in ‘Repulse’. Nevertheless, both cultivars had similar SAM diameter of 0.27-0.28 mm whenever reaching flower initiation even under various environmental conditions. When grown at 20/15℃, both cultivars with 4 h nightbreak (NB) had slower SAM and flower development, and longer time to flowering than those treated with 12 h photoperiod, especially for ‘Repulse’. Both cultivars remained vegetative growth under NB and 30/25℃ conditions for 120 days. When plants of ‘Kaa Luoh-Lii’ and ‘Repulse’ had reached flower initiation (Stage 2), they were then transferred to phytotrons with 30/25 and 20/15℃ under 12 h photoperiod and 4 h nightbreak (NB) conditions. Results showed that under 12 h photoperiod conditions, flower development and time to flowering in ‘Kaa Luoh-Lii’ did not differ between temperature treatments. In contrast, ‘Repulse’ at 30/25℃ had slower floral development and longer (36.2 d) time to flowering than those at 20/15℃. Both cultivars formed terminal crown buds at 30/25℃ under NB conditions. ‘Kaa Luoh-Lii’ had 1-2 rows of florets, while ‘Repulse’ did not have any floret, within the crown buds. Effects of temperature (30/25 and 20/15℃) on leaf relative injury (RI) value as measured with electrolyte leakage, malondialdehyde (MDA) concentration, and time to flowering were investigated in ‘Kaa Luoh-Lii’ and ‘Repulse’ vegetative plants under 11.5-12.5 h natural daylengths, or in those during flower development under 12 h photoperiod conditions. In ‘Kaa Luoh-Lii’, the 30/25℃ treatment resulted in reduced leaf RI value (42%-46%) on day 24 but did not increase leaf MDA concentration on day 12 and thereafter. Net photosynthesis rate, flower development, and time to flowering did not differ in ‘Kaa Luoh-Lii’ between temperature treatments during flower development. Contrastly, ‘Repulse’ at 30/25℃ had high leaf RI values (70%-80%) on day 24 and increased MDA concentration after day 12. Decreased net photosynthesis rate and delayed flower development and time to flowering were measured in ‘Repulse’ at 30/25℃ than at 20/15℃ during flower development. Shoot apical development and carbohydrate contents were measured in plants of ‘Kaa Luoh-Lii’ and ‘Repulse’ with 30/25 and 20/15℃ under 11.5-13.5 h natural daylength conditions. Results showed that ‘Kaa Luoh-Lii’ at two temperatures and ‘Repulse’ at 20/15℃ reached flower initiation approximately on day 9 after treatments. Both cultivars showed decreased sucrose and total soluble carbohydrates, and increased starch contents of shoot tips during the first 9 days. Maximal sucrose, total soluble carbohydrates, and starch contents of shoot tips were measured when florets initiated. ‘Repulse’ at 30/25℃ reached flower initiation on day 15, and thereafter had slower flower development, with lower sucrose, total soluble carbohydrates, and starch contents of shoot tips than those at 20/15℃. Dry weight of leaves and SAM development were measured in plants of both cultivars with 30/25 and 20/15℃ under 12 h photoperiod conditions. Results showed that in ‘Kaa Luoh-Lii’, dry weights of leaves positional and SAM development on days 10, 12, and 27 did not differ between temperature treatments. On days 10 and 12, ‘Repulse’ had heavier first 10 young leaves and slower SAM development at 30/25℃ than at 20/15℃. Young leaves competed carbohydrate assimilates with floral development that led to delay flowering in ‘Repulse’ at 30/25℃. Foliar spray with 25 and 50 mg•L-1 GA3 reduced time to show color and flowering for approximate 11 days in ‘Repulse’ at visible bud stage under 12 h photoperiod and 30/25℃ conditions. GA3 treatments also resulted in increased terminal flower bud diameter, decreased leaf and root dry mass fraction, but increased flower dry mass fraction. A single foliar spray with 50 mg•L-1 GA3 resulted in longer terminal flower peduncle, larger terminal flower bud diameter, and earlier flowering by 8 days than those without GA3 in ‘Repulse’ under natural long day (14-14.5 h) and high temperature (34.6℃) conditions.