青花菜AV531耐熱特性之探討

Abstract

青花菜性喜冷涼，臺灣夏季高溫常導致青花菜不結花球或花球品質不佳，為青花菜產出之空窗期，除了進口青花菜供應此時期需求外，培育青花菜耐熱品種十分重要。亞蔬－世界蔬菜中心新育出的青花菜品系AV531具早生、耐熱之特性，於21/15℃育苗，其五片真葉健壯苗受15/10℃低溫春化處理10天者，營養生長約41天可進入生殖生長，對照品種‘B75’則需55天；若不給予低溫春化處理，AV531經營養生長72天後仍可進入生殖生長，但‘B75’在試驗期間皆維持營養生長狀態達122天。在夏季(6~8月)田間的表現，AV531花芽分化率達95±3.3%，但‘B75’僅有2.5±2.5%。由此可知，此早生、耐熱品系AV531之春化需求並不嚴苛。本研究也在植株花芽分化階段給予35℃高溫逆境10天，此時期的高溫逆境對AV531花球發育影響不大，花球正常率達90%，畸形率為10%，而‘B75’花球正常率僅16.7%，花球畸形率高達83.3%。高溫逆境造成花序分生組織生長速率不整齊，導致花球發育早期即出現表面凹凸現象，甚至出現花蕾褐化敗育、萼片葉片化及花芽部分分化等情形，最後造成花球畸形、品質降低、提早鬆散。不同定植時間對AV531生長發育性狀有顯著影響，夏季植株無論營養性狀如株高、株幅、地上部鮮重及生殖性狀如花球莖粗、花球重量，數值皆較冬季植株小，彼此有顯著差異，而結球葉片數、花球直徑、花蕾厚度及長度則不依季節有所改變。AV531田間全年栽培之花球重量與地上部鮮重、花球莖粗及花球直徑之間具相關性，但與株高及株幅則無相關。AV531之耐熱生理指標包括細胞膜穩定度、葉綠素螢光Fv/Fm值、葉綠素計SPAD值、總葉綠素及丙二醛含量在高溫下皆較‘B75’穩定，且幼苗期葉片對高溫之敏感度較花芽分化期為高，故在青花菜大量育種材料作耐熱選拔時，可於植株幼苗期先使用非破壞性指標如SPAD值或Fv/Fm值做初步快速篩選，再以細胞膜熱穩定性作選拔確定之，縮短選種時間。

Broccoli (Brassica oleracea var. italica) is a cool-season vegetable, and the summer high temperature in Taiwan often leads to fail-heading or quality reduction. Besides imports to meet the demand in summer, breeding for heat tolerant cultivars is an important subject. AVRDC – The World Vegetable Center had developed broccoli line AV531 with early maturity and heat tolerance. Five-leaves seedlings grown at 21/15℃ were vernalized with 15/10℃ for 10 days. It took 41 d for AV531 to enter the reproductive growth versus 55 d for ‘B75’. In the non-vernalization treatment, AV531 needed 72 d to enter the reproductive growth while ‘B75’ remained in vegetative growth till the end of experiment for 122 d. In the field during June to August, 95±3.3% of AV531 plants underwent floral differentiation, and only 2.5 ± 2.5% of 'B75' plants did. Therefore, we concluded that the requirement of AV531 for vernalization is not strict. As we focused on the heat stress, 35℃ for 10 d in floral differentiation stage, 90% of AV531 plants produced normal curds, whereas only 16.7% of 'B75' plants did. Heat stress caused uneven inflorescence meristem growth which lead to uneven appearance in early curd development stage resulting of curd deformity including branchlet cluster, brown bead, leafy sepal, and incomplete flower differentiation. Growing season has significant influence on AV531 growth and development traits. Concerning of vegetative and reproductive characters, winter-grown AV531 plants were much more vigorous than summer grown plants except leaf number at curding, curd diameter, florets thickness and length. In the field planting throughout the year, the curd weight of AV531 was associated with shoot fresh weight, curd stem diameter, and curd diameter, but not with plant height and canopy. Under high temperature, physiological indicators include the thermostability of cell membrane, Fv/Fm values, SPAD values, total chlorophyll and malondialdehyde contents of AV531 showed higher stability than ‘B75’. Seedlings were more sensitive than floral differentiation stage plants. It was concluded that in large-scaled screening for heat resistant lines of broccoli, non-destructive indicators as SPAD and Fv/Fm values could be used in seedling stage for preliminary selection, then thermostability of cell membrane for further selection to fasten the breeding time.