Bioscience Evidence 2024, Vol.14, No.5, 195-205 http://bioscipublisher.com/index.php/be 200 5 Case Studies of Successful Hybrid Wheat Breeding 5.1 Hybridization between bread and durum wheat Hybridization between bread wheat (Triticum aestivumL.) and durum wheat (Triticum turgidumspp. durumDesf.) has led to the development of pentaploid hybrids with unique chromosomal constitutions. These hybrids can improve the genetic background of either parent by transferring traits of interest, such as disease resistance, abiotic tolerance, and grain quality. However, challenges such as low pollen compatibility, poor seed set, and frequent sterility in F1 hybrids have been noted. Careful selection of parental genotypes and using the higher ploidy level genotype as the maternal parent can overcome most of these barriers (Padmanaban et al., 2017). In another study, durum wheat was proposed as the female progenitor of bread wheat. Crosses between a durum wheat cultivar carrying a gene for meiotic restitution and Aegilops tauschii produced highly fertile triploid F1 hybrids without the need for embryo rescue techniques. These hybrids spontaneously set hexaploid F2 seeds, demonstrating high fertility and vigorous growth habits, which supports the theory of durum wheat being a progenitor of bread wheat (Matsuoka and Nasuda, 2004). 5.2 Overcoming hybrid lethality using embryo culture: breaking wheat-rye reproductive barriers Hybrid lethality is a significant barrier in wheat-rye hybridization, often resulting from the interaction of incompatible genes. In situ embryo rescue techniques have been employed to overcome this barrier. By culturing immature embryos via callus induction, researchers have successfully regenerated plantlets from abnormal embryos. This method has shown that the reproductive barrier in wheat-rye hybrids may have an epigenetic origin, which can be mitigated through in vitro culture methods. Despite the success in overcoming embryo lethality, challenges such as pollen and embryo sac sterility remain, affecting both male and female gametophytes (Tikhenko et al., 2017). Further analysis of hybrid lethality in F1 wheat-rye hybrid embryos revealed that the Embryo lethality mutant (Eml) of rye arrests the formation of the shoot meristem but does not affect the root meristem. This lethality could not be overcome by direct regeneration on Kruse medium, indicating the need for alternative approaches to address gene expression variations during hybrid formation (Tikhenko et al., 2008). Wide hybridization experiments have also been conducted with cereals, including wheat, barley, and rye, using various species of the Poaceae and Panicoideae families. Embryo formation was achieved with several species, and new embryo culture techniques have enabled these embryos to grow into plants, demonstrating the potential for overcoming hybridization barriers in cereals. 6 Applications of Hybrid Wheat in Modern Agriculture 6.1 Enhancing yield in marginal environments Hybrid wheat has shown significant potential in improving yield potential in stress-prone environments. The development of hybrid wheat varieties can address the challenges posed by abiotic stresses such as drought, heat, and poor soil conditions. For instance, hybrid wheat cultivars have demonstrated higher stress resistance and better performance under drought conditions compared to traditional line cultivars (Prey et al., 2019). Additionally, the use of innovative breeding strategies and genetic diversity has been essential in developing wheat varieties that can thrive in marginal environments, thereby enhancing productivity and food security (Mondal, 2016; Tshikunde et al., 2019). Prey et al. (2019) revealed the yield potential of hybrid wheat in marginal environments, particularly showing significant hybrid vigor in traits such as grain yield, nitrogen uptake efficiency, and biomass accumulation compared to inbred lines. The hybrid vigor for some traits exhibited considerable variation across different years, indicating that environmental factors play an important role in the trait performance of hybrid wheat. Although certain traits may display negative hybrid vigor in marginal environments, the overall trend demonstrates the potential of hybrid varieties for yield improvement and enhanced nitrogen use efficiency, providing strong evidence for the development of high-yielding hybrid wheat in challenging environments (Figure 3).
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