Developing fundamentals for breeding of new ornamentals using the example of midday flowers

Abstract

For most new ornamentals, fundamental knowledge on the respective species and genera is largely missing that is needed to establish breeding methods, including interspecific and intergeneric hybridization and polyploidization. Using the example of midday flowers (Aizoaceae) which are interesting candidates for new ornamentals due to their special and very intense flower colours and their drought tolerance, investigations on flower development, DNA contents, and crossing compatibility are presented. An obligate photoperiodic reaction was not dectable for any of the genotypes of the genera Cephalophyllum, Lampranthus, and Delosperma, whereas different reactions to daily mean temperatures were observed depending on the genus.
In cross pollination experiments within and among the genera Lampranthus and Delosperma, late acting pre-zygotic hybridization barriers were recorded in some interspecific and intergeneric combinations. However, post-zygotic barriers were observed more frequently, resulting in delayed and abnormal development of the zygotic embryo, chlorophyll deficiencies and low vigour of the offspring. By employing in vitro sowing and embryo rescue techniques, few interspecific and intergeneric hybrids were obtained, the hybrid status of which was confirmed by AFLP markers.
Aiming at the detection of unreduced gametes pollen grains were analysed. It turned out that flow cytometric analyses may lead to misinterpretation of the data, because pairs of sperm nuclei as well as complete male germ units (MGU) result in peaks at the 2C or 3C position, respectively. Pollen nuclei were useful for the estimation of DNA contents: In Delosperma and Lampranthus, the DNA contents ranged from 1.18 pg/2C to 3.68 pg/2C and from 1.6 pg/2C to 2.36 pg/2C, respectively.
The tissues of all analyzed plant organs consisted of cells with up to five different DNA amounts (2C-32C). High proportions of endoreduplicated cells were detected in cotyledons (74-87 %), petals (56-95 %) and older, fully expanded leaves (64-90 %), whereas organs with lower portions, such as roots (23-34 %), internodes (29-45 %) and young leaves (17-56 %) might be well-suited for in vitro shoot regeneration and polyploidization, since endoreduplicated cells are assumed to lose their ability for mitotic cell division.