Effects of temperature and auxin treatment on fruit set and pigmentation of Dodonaea ‘Dana’

Abstract

Dodonaea ‘Dana’ is a natural hybrid (Dodonaea viscosa purpureaxDodonaea aptera) cultivated for the production of decorative cut branches bearing dark red foliage with red fruit. This hybrid flowers throughout the year in the Mediterranean climate, but fruit set occurs only during the winter, leading to a short two month period of fruit bearing branches. The aim of this work was to characterize the environmental conditions affecting fruit set in D. ‘Dana’ plants, and improve the efficiency under sub-optimal conditions by hormonal treatment of the plants. When plants were grown at different temperature regimes the number of fruit developed from each inflorescence was 3-fold higher in plants grown at 17°C/9°C, in comparison to 29°C/21°C, suggesting that temperature is a critical factor for the development of D. ‘Dana’ fruit. In addition, the anthocyanin concentration of fruit grown at the lower temperature regime was four times higher than those grown at the elevated temperature. To improve fruit setting in plants grown at moderate or elevated temperatures (23°C/15°C and 29°C/21°C), individual inflorescences were treated with one of the two synthetic auxins, naphthalene-1-acetic acid (NAA) and 4-chlorophenoxy acetic acid (4-CPA). Both auxins increased the number of set fruit per inflorescence at both temperature regimes, with an advantage to the NAA treatment at the 23°C/15°C regime. Treatment of whole plants with either NAA or 4-CPA at 26°C/18°C (day/night respectively) regime, caused a significant increase (2.5–3-fold) in the number of inflorescences per branch with no visual effect on the vegetative characteristics of the plants. In addition, NAA treatment caused an increase of over 50% in the number of flowers per inflorescence. Similar to the treatment of individual inflorescences, here too both synthetic auxins improved the yield of fruit setting.