Breeding of hybrid male-sterile ornamental sunflowers and evaluation of their ornamental potentials

Sunflower (Helianthus annuus L.) was solely used as an ornamental plant until the 18th century. It is used in landscaping as a border plant and in combination with other ornamental plants, both indoors and outdoors. Sunflowers are also used as potted ornamental plants and as cut flowers. Vase life is considered as a significant selection criteria for cut flower breeders and sterile varieties have a longer vase life in comparison to fertile varieties due to the reduced ethylene synthesis. Ornamental sunflower has a wide range of colors such as purple, orange, yellow, light-yellow, red-brown, white, and lemon-yellow colors. The objective of this study was to investigate male-sterile ornamental sunflower hybrids for vase life, flower colors, and plant structures. In this context, A (CMS) and B (maintainer) lines developed using CMS method within the scope of TUBITAK project 122R004, resistant to Sulfonylurea group herbicides, were crossed and male-sterile hybrids were obtained. Morphological traits such as flowering time, germination time and rate, branching status and position, flower head attitude, plant height, stem length, flower head diameter, stem diameter, disc diameter, ray flower characteristics, pollen fertility, leaf size and color, the color of the ray flowers (petal) and disc flowers (sexual flowers) were investigated to determine the ornamental potential of the hybrids obtained. The results demonstrated that the vase life of 31 variety candidates varied between 9.2 and 14 days. The vase life of commercial varieties used for control/check ranged from 8 to 11 days. These results were achieved without any vase solution indicating that variety candidates exhibited high quality, robust plant structures, genetic superiority, and high market potential. Furthermore, according to the observations conducted to determine the ornamental potential of hybrid variety candidates, it was concluded that 15 candidates were suitable for outdoor ornamental plants in landscaping areas and public spaces, 12 candidates were found to be desirable for cut flower purposes, and, four dwarf-type candidates were determined to be suitable for use as potted plants. Within the investigation of ray flower color inheritance studies, the ray flower color of male-sterile hybrids were compared with parental lines. The results indicated the dominant colors and which parental combinations should be used in crosses to obtain the desired ray flower color. It was observed that yellow color was dominant over orange and lemon colors, and several color variations such as purple, red, lemon and apricot colors were achieved by crossing parental lines with different gaillardia tones. Red, orange, lemon, and reddish-brown, exhibited genotypic recessiveness and were phenotypically less prevalent in the majority of hybrids. This study highlighted important features on the inheritance of ray flower color traits in ornamental sunflowers, providing directions in achieving desirable color variations in ornamental crops. It also provided important and useful informations for hybrid breeding projects in the development of ornamental sunflower variety candidates and achieving various colors and tones suitable for the market.