Study on Heat Tolerance of Brassica oleracea var. italica AV531
Date Issued
2010
Date
2010
Author(s)
Chen, Mei-Lan
Abstract
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.
Subjects
vernalization
thermostability of cell membrane
Fv/Fm values
SPAD values
total chlorophyll contents
malondialdehyde contents
Type
thesis
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