Tree Genetics and Molecular Breeding 2024, Vol.14, No.1, 1-7 http://genbreedpublisher.com/index.php/tgmb 2 2 Genetic Diversity of Apple Germplasm Resources 2.1 The origin and evolution of apple The apple (Malus domestica), as an ancient and precious fruit, has gone through a long history of its origin and evolution, containing rich traces of cultural and human activities. The origin of apple can be traced back to Asia and Europe, where wild apple trees initially grew in the high mountains of Asia, forming the earliest apple gene pool (Figure 1) (Gao et al., 2015). Figure 1 The distribution of apples around the world (Adopted from Wang et al., 2018) Image caption: Malus sieversii in Central Asia, Malus sylvestris in Europe, and Malus orientalis in Caucasus were originally proposed to be ancestors of cultivated apple (Adopted from Wang et al., 2018) These wild apple trees not only gradually evolved diversity in their natural environment, but also became an important part of human agricultural civilization. Early human communities began to recognize the edible value of wild apples, and gradually formed the earliest artificial varieties through selective breeding and cultivation practices. This process is not only the domestication and improvement of plants, but also the product of the interaction between man and nature. With the expansion of cultural exchanges and trade, apples gradually spread to all parts of the world. The ancient trade and wars promoted the introduction of apples from Asia to Europe, and also gave birth to the traditions of apple cultivation in different regions. In this process, people through the continuous selection, breeding and reproduction to create a unique variety of apple. The origin and evolution of the apple is not only the subject of botany and genetics, but also a story throughout the history of human civilization. Woven into the story is the wisdom of the mutual domestication of man and nature, as well as the diversity formed through cultural exchange. A thorough understanding of the origin of apple will help people better understand the role of this fruit in human civilization, and also provide scientific basis for subsequent discussions on apple genetic diversity and conservation strategies. 2.2 Methods for determining genetic diversity The method of genetic diversity determination is very important for the conservation and utilization of apple germplasm resources. In exploring the genetic diversity of apple germplasm resources, scientists have adopted various methods. Among them, molecular marker technology is one of the most commonly used means to evaluate the genetic diversity of apple, by analyzing DNA or RNA sequences, such as random amplified polymorphic DNA (RAPD), simple repeat sequence (SSR), single nucleotide polymorphism (SNP), etc. It can reveal genetic differences and levels of diversity between different apple varieties (Ahmad et al., 2021). Morphological characteristics are also one of the important methods to evaluate the genetic diversity of apple, and researchers reveal the differences and variations among different varieties through quantitative and qualitative analysis of fruit morphology, leaf characteristics, tree structure, etc. Assessment of biological characteristics is also key to determining genetic diversity. The observation and recording of growth habits, flowering period, fruiting characteristics, etc., can provide information about differences between varieties, and then judge their genetic diversity.
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