Molecular Plant Breeding 2024, Vol.15, No.4, 187-197 http://genbreedpublisher.com/index.php/mpb 188 MAS in Camellia breeding, enhance the efficiency and success of MAS in Camellia, and explore its potential to revolutionize the development of superior Camellia varieties. 2 Overview of Camellia Species and Breeding Objectives 2.1 Diversity and distribution of Camellia species The genus Camellia comprises over 250 species, predominantly distributed in East Asia, particularly in China, Japan, and Korea. These species exhibit significant diversity in morphology, habitat, and ecological adaptability. For instance, Camellia sinensis is widely cultivated for tea production (Guo et al., 2024; Zhang et al., 2024), while Camellia oleifera is valued for its oil-rich seeds (Sharma et al., 2009; Feng et al., 2020; Tian et al., 2022). The genetic diversity within and among Camellia species is substantial, as evidenced by various molecular marker studies, which have revealed high levels of polymorphism and heterozygosity (Sharma et al., 2009; Tan et al., 2013; Tian et al., 2022). This diversity is crucial for breeding programs aimed at improving both ornamental and economic traits. 2.2 Breeding objectives for ornamental and economic traits 2.2.1 Flower color and shape Flower color and shape are critical ornamental traits in Camellia breeding. The diversity in petal color and flower morphology among Camellia species and cultivars is significant, with colors ranging from white to deep red and various shapes from single to double petals. Molecular markers, such as RAPD and SSR, have been used to correlate genetic diversity with these morphological traits, aiding in the selection of desirable phenotypes (Wang et al., 2011). 2.2.2 Disease resistance Disease resistance is a vital breeding objective, particularly for fungal diseases like blister blight, which can cause substantial crop losses. Marker-assisted selection (MAS) has been employed to identify and incorporate resistance genes into breeding lines. For example, an EST-SSR marker associated with blister blight resistance has been identified in Camellia sinensis, facilitating the development of resistant cultivars. The use of molecular markers accelerates the breeding process and enhances the accuracy of selecting disease-resistant plants (Foolad and Panthee, 2012; Miedaner and Korzun, 2012; Karunarathna et al., 2020). 2.2.3 Cold tolerance Cold tolerance is another important trait, especially for Camellia species grown in temperate regions. Breeding for cold tolerance involves selecting genotypes that can withstand low temperatures without significant damage. Genetic studies have shown that cold tolerance is a heritable trait, and molecular markers can be used to identify and select cold-tolerant genotypes in breeding programs (Feng et al., 2020; Tian et al., 2022). 2.2.4 Oil content and quality For species like Camellia oleifera, oil content and quality are primary economic traits. Breeding programs aim to enhance oil yield and improve the fatty acid composition of the oil. Studies have shown that traits related to oil content, such as fruit diameter, seed weight, and oil quality, exhibit high heritability, making them suitable targets for selection. The use of molecular markers, such as SRAP and SSR, has been instrumental in identifying genetic loci associated with these traits, thereby guiding the selection of superior genotypes (Feng et al., 2020; Tian et al., 2022). 3 Genetic Markers inCamellia 3.1 Types of genetic markers used in plant breeding 3.1.1 Morphological markers Morphological markers are phenotypic traits that can be visually observed and measured, such as flower color, leaf shape, and plant height. These markers have been traditionally used in plant breeding due to their simplicity and ease of observation. However, they are often influenced by environmental factors and may not always accurately reflect the genetic makeup of the plant.
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