The effects of parent selection in cross-breeding on fruit and seed characteristics of dragon fruit (Hylocereus spp.)

Global climate change has caused significant changes in the agricultural patterns of countries worldwide. It is thought that these changes may bring some benefits to our country's agriculture. Among these advantages, the opportunity to cultivate tropical fruits both in the open field and in the greenhouses can be shown. Due to our country's closeness to European countries, the possibility of export when these tropical species are grown, and the maintenance of price stability has led to an increase in the interest of producers in cultivating these species. One of the most important tropical species is dragon fruit, which can be easily propagated by cuttings and bears fruit in the second year. Moreover, the harvesting period is divided into months throughout the year, bringing the dragon fruit to the forefront for cultivation. However, the pollination problems of pitaya and dependency on foreign countries for cultivar selection have brought this thesis topic to the agenda. The first objective of this study was to create an infrastructure for prospective breeding programs by making inter- and intra-specific hybridization in dragon fruit. The second objective was to investigate the metazenic (changes in fruit characteristics due to cross-pollination) effects of cross-pollination on fruit yield and quality, and zenic (changes in seed characteristics due to cross-pollination) impacts of cross-pollination on seed characteristics. In this study, white x white, red x red, white x red, and red x parent showing white characteristics were selected as parents. A total of 25 hybrid combinations were applied in the experiments. Reciprocal crosses were made by emasculating the male organs of the varieties to be used for hybridization purposes. To prevent any unwanted cross-pollination, each pollinated flower was carefully covered. Harvesting was then carried out at the optimal time for fruits that had successfully set. In addition, several measurements including, fruit weight, fruit length, fruit width, index value, fruit peel color, fruit flesh color, fruit flesh hardness, fruit flesh weight, fruit peel weight, fruit peel thickness, water-soluble dry matter (WSS) amount, and titratable acid (TEA) values, were taken from harvested fruits. Furthermore, the samples were tested for vitamin C, antioxidant activity, total flavonoid amount, total phenolic substance amount, and anthocyanin. Studies indicate that cross-pollination plays a vital role in determining the weight of fruits, a crucial factor in commercial cultivation. Highest fruit weight was determined as 480.09 g in Costa Rica White (KB) x Vietnam Jaina (VJ) hybridization combination. Generally, self-pollination negatively affected fruit weight and size compared to cross-pollination. When the crossing effect on the index was examined, it was determined that the fruits obtained from these crosses in which the Ruby Red (RR) variety, due to the shorter fruit length, used as the female parent were more rounded in shape compared to the crosses in which the Vietnamese White (VW) and VJ varieties were the female parents. The highest fruit flesh weights are observed in the cross combinations of KB x VJ (400.02 g) and KB x Dark Star (DS) (348.49 g). The lowest fruit flesh weights were determined in the self-pollinated combinations of KB x KB (75.53 g) and RR x RR (84.20 g). It is a desired feature that the fruit peel weight and fruit peel thickness should be thin in fruits sold as pieces. The lowest fruit shell thickness was recorded in the cross of DS x KB. The amount of water soluble dry matter value is one of the most important quality criteria for dragon fruit. When the crosses were examined, the highest TSC values were determined as 13.73% [RR x Thai Red (TK)], 13.30% (KB x DS) and 13.20% (KB x VJ). Cross-pollination resulted in changes in both fruit skin color and fruit flesh color. Fruit biochemical properties varied according to maternal and paternal parents. It was also determined that interspecific hybridization did not affect seed germination. Based on our research, it was determined that the maternal parent plays a crucial role in fruit color, while cross-pollination has a positive impact on fruit size. It is also thought that there is a metazenic and zenic effect in pitaya in terms of fruit and seed characteristics. Therefore, it has been recommended to select maternal and paternal parents based on desired yield and quality parameters and take this into account when planning plantations.