Preface

This Edited Volume is a collection of reviewed and relevant research chapters, concerning the developments within the Current and Emerging Challenges in the Diseases of Trees field of study. The book includes scholarly contributions by various authors and is edited by a group of experts pertinent to Agricultural and Biological Sciences. Each contribution comes as a separate chapter complete in itself but directly related to the book's topics and objectives.

The Book includes the following chapters dealing with the topics: "Devious Phloem Intruder *Candidatus* Liberibacter Species Causing Huanglongbing: History, Symptoms, Mechanism, and Current Strategies", "Anthracnose Disease of Mango: Epidemiology, Impact and Management Options", "New and Emerging Disease Threats to Forest Plantations in Sarawak Borneo, Malaysia", "Main Pests and Diseases in Tropical Forest Species in Nursery" and "Perspective Chapter: Microorganisms and Their Relationship with Tree Health". The target audience comprises scholars and specialists in the field.

**IntechOpen**

**1**

**Chapter 1**

**Abstract**

Devious Phloem Intruder

Current Strategies

elimination of HLB pathogens.

**1. Introduction**

*Candidatus* Liberibacter Species

Symptoms, Mechanism, and

Causing Huanglongbing: History,

*Palaniyandi Karuppaiya, Junyuan Huang and Muqing Zhang*

Huanglongbing (HLB) or greening is a devastating phloem-intruding bacterial disease that generates various symptoms in leaves and fruits, threatening the global citrus industry. *Candidatus* Liberibacter asiaticus, *Candidatus* Liberibacter africanus, and *Candidatus* Liberibacter americanus are the causative agents of HLB in citrus-producing regions around many countries, and these proteobacteria are being vectorized by *Diaphorina citri* and *Triozaerytreae*. The lack of HLB-resistant citrus cultivars, the rapid spread of disease, and the fastidious nature of HLBproteobacteria have made it difficult to mitigate HLB in the citrus field. There are numerous reports on the control of HLB disease using thermotherapy, chemotherapy, plant defense activators, brassinosteroids, and nanoemulsions. However, there is no evidence of such applicability of the methods mentioned above to complete the elimination or suppression of the pathogen to control HLB disease. We aim to provide an overall picture of HLB disease, its distribution, causal organism, pathogenic mechanism, and current and future strategies for combat against citrus Huanglongbing disease. This review may prompt the researchers toward an integrated and environmentally sustainable methodology for the mitigation/

**Keywords:** citrus, Huanglongbing, *Candidatus* Liberibacter, control strategy, psyllid

Citrus fruits are the most predominantly produced fruits worldwide. The citrus species, Rutaceae family, is one of the major fruit crops in the world, which has provided an immune-enhancing source of vitamin C, nutrients, and medicinal value since ancient times [1]. Citrus crops are cultivated in more than 135 countries worldwide [2]. Worldwide citrus production is estimated at over 124.3 million tons annually [3]. Cultivated commercial citrus plants, consisting of rootstock and scion
