Articles
Characteristics and heritability of floral morphology for the double flower trait in evergreen azalea
Article number
1434_25
Pages
177 – 182
Language
English
Abstract
Double flower form is an important trait of ornamental flower plants such as Japanese azalea because of its high visual appeal.
Morphological variations of azaleas include double flowers, in which the stamens and pistils are transformed into petals, and hose-in-hose flowers, in which the sepals are transformed into petals.
To characterize the double flower trait of azalea, detailed observations of floral morphology and the heritability of the double-flower trait were investigated in this study.
Observation of the floral structure during flowering revealed the following three types: 1) full double flower type (A), in which stamens and pistils are completely transformed into petals, as in Rhododendron indicum ‘Kō-man-e’; 2) semi-double flower type (B), in which some of the petaloid stamens have attached anthers and filaments, or the inside of the stamen transforms into sepals to form secondary flowers, as in R. × mucronatum ‘Shiro-man-yō’; and 3) semi-double flower type (C) in which the stamens are completely transformed into petals and normal pistils remain, as in Azalea ‘Roze-net’. F1 hybrids crossed between single flower and double flower cultivars with stamens, such as ‘Shiro-man-yō’ or ‘Ambrosius’, produced only single flowers with normal stamens and pistils.
On the other hand, single and double flowers appeared in the F1 hybrid crossed with ‘Rose net’. In the double-flowered azalea cultivar, the Agamous genes required for stamen and pistil formation in wholes 3 and 4 were not expressed in organs completely transformed into petals but were expressed in organs with partially stamens and normal pistils in ‘Rose net’. These results suggest that the transformation of stamens and pistils into petals in azaleas is related to absence of AG gene expression but is a morphologically and genetically distinct trait among cultivars.
Morphological variations of azaleas include double flowers, in which the stamens and pistils are transformed into petals, and hose-in-hose flowers, in which the sepals are transformed into petals.
To characterize the double flower trait of azalea, detailed observations of floral morphology and the heritability of the double-flower trait were investigated in this study.
Observation of the floral structure during flowering revealed the following three types: 1) full double flower type (A), in which stamens and pistils are completely transformed into petals, as in Rhododendron indicum ‘Kō-man-e’; 2) semi-double flower type (B), in which some of the petaloid stamens have attached anthers and filaments, or the inside of the stamen transforms into sepals to form secondary flowers, as in R. × mucronatum ‘Shiro-man-yō’; and 3) semi-double flower type (C) in which the stamens are completely transformed into petals and normal pistils remain, as in Azalea ‘Roze-net’. F1 hybrids crossed between single flower and double flower cultivars with stamens, such as ‘Shiro-man-yō’ or ‘Ambrosius’, produced only single flowers with normal stamens and pistils.
On the other hand, single and double flowers appeared in the F1 hybrid crossed with ‘Rose net’. In the double-flowered azalea cultivar, the Agamous genes required for stamen and pistil formation in wholes 3 and 4 were not expressed in organs completely transformed into petals but were expressed in organs with partially stamens and normal pistils in ‘Rose net’. These results suggest that the transformation of stamens and pistils into petals in azaleas is related to absence of AG gene expression but is a morphologically and genetically distinct trait among cultivars.
Authors
T. Eto, N. Kobayashi, A. Nakatsuka
Keywords
Agamous, petaloid, pistil, semi double flower, stamen
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