Reviews on Asian citrus species: Exploring traditional uses, biochemistry, conservation, and disease resistance

The species of genus Citrus mostly originated in Southeast Asia, a region with a remarkable diversity of Citrus species. They have been cultivated and harnessed worldwide and are commonly known as mandarins, oranges, lemons, and pomelos. The major products of the plants include the juice from fruits, leaves, and the rind as flavour enhancement of food in many regional culinary cultures. Different parts of the plants are commonly used in traditional medicines with a long history ascribed to the potential medicinal benefits, including antimicrobial, antihypertensive, anti-inflammatory, and antioxidant properties. In this article, we aim to provide a comprehensive review of studies on Citrus species in the following aspects. First, we reviewed studies on various Citrus species in different geographic regions of Asia including their uses in medicinal, culinary, and other cultural purposes. The phylogeny of the Citrus species was proposed to be complicated, which might be attributed to the extensive interbreeding between ancestral taxa and/or being cultivated for different economic strains. Secondly, we summarized and discussed the studies of Citrus depressa in Japan and Taiwan, emphasizing the maintenance of genetic diversity and the potential health benefits of bioactive compounds. Finally, we reviewed the studies discovering the species or cultivars that may provide a source of disease-resistant genes to help Citrus plants from Huanglongbing (HLB), a common disease of Citrus species. The use of the latest genomic biotechnology to introduce disease-resistant genes to cultivars will significantly reduce the damage to the soil and environment from using chemical reagents for disease prevention.