In the study of plants, the above-ground part is often studied intuitively, while the below-ground part is neglected. In fact, there is a beneficial group of arbuscular mycorrhizal fungi that inhabit the rhizosphere of plants, capable of colonizing approximately 72% of terrestrial plant roots and establishing an arbuscular mycorrhizal symbiosis. In the root system, a characteristic of this symbiosis is the establishment of a well-developed network of extraradical hyphae outside the root system and involved in the uptake and transfer of both nutrients and water from the soil, thus providing a rapid highway from the soil to the host plant. Furthermore, the extraradical mycelial network also connects neighbouring identical or different plants into an organic association for pest and disease defence as well as nutrient transfer. Mycorrhizal network plays a critical role in nutrient redistribution and stress tolerance in ecosystems.
Citrus as a worldwide fruit tree, is grown in many countries such as China, Spain, the United States of America, Brazil, Australia, India and so on. Because citrus is a shallow root plant, it is very short of root hair. Therefore, it is highly dependent on the colonization of arbuscular mycorrhizal fungi from the soil into the root system to establish arbuscular mycorrhizal symbionts, which can partially replace the nutrient and water absorption function of root hair. Thus, mycorrhizal fungi can be opened up as a biological fertilizer to be used in citrus cultivation. It is very necessary to carry out mycorrhizal research on citrus to maintain the growth of organic citrus.
This book is written on the basis of such research. The book is divided into seven chapters. Chapter 1 provided a comprehensive overview of the role of arbuscular mycorrhizal fungi on citrus, focusing on growth, nutrient uptake, root hairs, and stress resistance. Chapter 2 clarified the use of SSU rRNA to identify AMF populations in citrus roots and soil in the field. Chapter 3 presented three propagation methods for indigenous AMF of citrus. Chapter 4 compared four different AMF inoculation methods in citrus at the nursery, and clarified that one-layer inoculation of AMF was the preferred method for mycorrhizalization in citrus seedlings. Chapter 5 pointed out the preference for steam sterilization of growth substrates accompanied by oven and UV light for mycorrhizalization of citrus seedling. In chapter 6, AMF were inoculated on field Ponkan, and the potential of AMF application on fruit quality and mycorrhizal development of citrus was evaluated. For the management of mycorrhizas in citrus orchards, Chapter 7 explicitly gave some field considerations. In conclusion, this book comprehensively summarized the role of mycorrhiza in citrus, with emphasis on the application and evaluation of mycorrhiza in the field, the propagation of mycorrhiza fungi, the inoculation methods of arbuscular mycorrhiza fungi, the sterilization methods of growth substrates, and the management of citrus mycorrhiza in the field.
Here, we would like to sincerely thank our doctoral supervisor, Professor Ren-Xue Xia of Huazhong Agricultural University, for his suggestion that we enter the research field of citrus mycorrhizas and stick to it all the time.
The work of the book is supported by the Hubei Agricultural Science and Technology Innovation Action Project (Hubei Nongfa  No. 1) and the Project of Innovation and Entrepreneurship Course Textbooks of Yangtze University.
The book is published with the support of B P International, and we are extremely grateful to the editors of B P International for their productive contributions to the editing and publication of the book. This book is an extension of some articles published by the editors in the journals and conferences. As a result, the various chapters in the book may have some flaws. In addition, there are some references in the book that did not be quoted. The ability and level of the editors is limited, the book inevitably has shortcomings, sure everyone's tolerance and criticism.
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