International Journal of Horticulture, 2024, Vol.14, No.4, 263-274 http://hortherbpublisher.com/index.php/ijh 269 By integrating genomics and metabolomics, this research not only identified candidate terpenes related to resistance and the genes involved in their synthesis but also validated the antifungal activity of some terpenes through in vitro experiments. This provides a theoretical basis and molecular tools for future development of carrot varieties with enhanced disease resistance. 5 Genetic and Environmental Factors 5.1 Influence of genetic variability on carrot traits Genetic variation is a key factor in determining the traits of carrot plants, directly influencing important agronomic characteristics such as yield, disease resistance, and quality. Research has shown that there is significant genetic diversity within carrot populations, providing valuable resources for breeding efforts. By evaluating 36 different carrot genotypes, it was found that selecting varieties with superior root quality could lead to significant indirect improvements in other traits. This suggests that fully utilizing genetic variation can not only directly enhance a specific trait but also contribute to the overall improvement of agronomic traits, making it a crucial aspect of breeding programs (Carvalho et al., 2019). Additionally, the genetic diversity structure of Western-type carrots has been extensively studied. Although these varieties exhibit high phenotypic stability, they still possess a high level of internal genetic heterogeneity (Stelmach et al., 2021). This inherent genetic diversity provides an important foundation for variety improvement, enabling breeders to further develop new varieties with desirable traits while maintaining stable phenotypes. Therefore, a deep understanding and utilization of carrot genetic diversity not only help meet the market demand for high-quality carrots but also promote the sustainable development of carrot cultivation. By considering both genetic variation and environmental impacts, carrot breeding will be better equipped to address current and future agricultural challenges. 5.2 Environmental impacts on carrot growth Environmental factors play a crucial role in the growth and development of carrots. Various environmental conditions can significantly affect traits such as root yield, disease resistance, and nutrient content in carrots. Factors such as soil fertility, temperature, humidity, light, and water supply can directly or indirectly influence the growth performance of carrots. Under certain environmental conditions, carrots may exhibit higher root yields and stronger disease resistance, while under adverse conditions, these traits may be suppressed or weakened. In a study conducted in the low hill region of Himachal Pradesh, India, researchers observed that the phenotypic coefficient of variation (PCV) for all traits was greater than the genotypic coefficient of variation (GCV), indicating a significant influence of the environment on trait expression (Rana et al., 2022). This phenomenon highlights the critical role of environmental conditions in carrot breeding and cultivation, emphasizing the need for careful consideration. Moreover, environmental stresses such as drought and high temperatures can adversely affect carrot growth. However, with advancements in biotechnology, it has become possible to enhance carrot stress tolerance through genetic improvement. For example, overexpression of the DcBCH1 gene in Arabidopsis thaliana has shown increased drought tolerance, indicating that genetic modifications can help plants better cope with environmental stresses (Li et al., 2021). This genetic engineering approach provides new directions and strategies for stress-resistant carrot breeding, especially in the face of increasing climate change and extreme weather conditions. By combining genetic improvement with environmental management, carrot growers can better cope with complex and variable environmental conditions, ensuring stable yields and quality of carrots. 5.3 Interaction between genetics and environment in carrot breeding The interaction between genetic and environmental factors is critical in carrot breeding programs. The combined effects of genetics and environment can influence the success of breeding efforts aimed at improving yield and disease resistance. For instance, the identification of resistance QTLs (rQTLs) and metabolite QTLs (mQTLs) in carrots has shown that it is possible to select for both resistance to Alternaria dauci and low bitterness by targeting specific genomic regions, taking into account the environmental conditions in which the plants are grown (Clerc
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