Temperature-dependent Flower Malformation in Carnations (<i>Dianthus caryophyllus</i> L.)

Abstract

Temperature regimes that cause malformed flowers were examined and histological observation was carried out at the developmental stage of flowers by using mutants of the potted carnation (Dianthus caryophyllus L.) 'Cherry' producing malformed flowers according to cultivation season. Plants of normal (WT) and malformed (mlf) lines were grown under several temperature regimes. All WT plants produced normal flowers, whereas mlf lines showed a variety of malformed floral phenotypes, including phyllody-like proliferated sepaloids, proliferated petaloids, proliferated pistillodes with or without petals, secondary flower formation, and a flattened receptacle. In Experiment 1, mlf plants produced no malformed flowers when grown under constant 26°C, whereas 34.2% of mlf plants produced malformed flowers at 14-16/12°C (day/night, natural light). Malformation frequency was slightly lower at a night temperature of 5°C compared with 14-16/12°C. When malformed mlf plants were transferred from 17/5°C to 23/18°C, flower malformation was alleviated. Conversely, when mlf plants grown under constant 26°C with a normal phenotype were transferred to 17/12°C, flower malformation was induced. Thus, flower malformation was reversible depending on the temperature regime. In Experiment 2, 92.2% of mlf plants produced malformed flowers under constant 15°C, whereas 3.1% and 1.3% showed flower malformation when grown under constant 20°C and 25/20°C, respectively. These findings suggested that the threshold for flower malformation is between 15°C and 20°C. Observation of shoot apices by optical microscopy and scanning electron microscopy revealed morphological differences between WT and mlf after sepal formation. Petal primordia were not visible in mlf plants at 15°C, although petal primordia were initiated in WT. After this stage, flower malformations observed in mlf included undeveloped petals, undeveloped or irregularly developed stamens, secondary flower primordia formation, and completely irregular arrangement of undeveloped flower organs. No phytoplasma was detected by PCR, indicating that it could not be the causal agent of the abnormal phenotypes. This is the first report of mutant flower phenotypes dependent on temperature and induced by only a 5°C difference within optimal growing-temperature regimes in carnations.

Seasonal variation of two floral patterns in Clematis ‘Vyvyan Pennell’ and its underlying mechanism

“…Previous studies have demonstrated that the development of stamens in certain plant species can be influenced by temperature, with the specific effects being contingent upon the varying sensitivities. In a study on Dianthus caryophyllus ‘Cherie’, malformed flowers with irregularly developed stamens were induced at 15–20 ℃ [ 23 ]. Similarly, short-term high (35 ℃) or low (2 ℃) temperatures may cause high malformation rates of flowers in strawberry cultivars ‘Maehyang’ and ‘Seolhyang’ [ 63 ].…”

“…Besides differences in floral development, ambient temperature and endogenous hormones are essential for the regulation of floral structure. In some varieties, such as Dianthus caryophyllus ‘Cherie’ and Cyclamen persicum ‘Wink Pink II,’ the number of petals changes in response to artificially controlled low- and high-temperatures [ 23 , 24 ]. Typically, relatively cold temperatures (ranging from 5 to 15 ℃) stimulate more floral organs, which were often originated from proliferating petals or petaloid stamens.…”