Mycorrhizas in citrus : Beyond soil fertility and plant nutrition

Abstract

Citrus, one of the important fruit trees grown in tropical and subtropical regions of the world, has less and shorter root hairs in the field, thus, highly dependent on arbuscular mycorrhizas. Citrus rhizosphere inhabits 45 species of arbuscular mycorrhizal fungi (AMF), belonging to seven genera like Acaulospora, Entrophospora, Gigaspora, Glomus, Pacispora, Sclerocystis and Scutellospora. These AMF can be associated with the roots for the formation of arbuscular mycorrhizal symbiosis, who would enlarge the contacted areas of roots to soil and be regarded as a potential soil biofertilizer, thereby promoting citrus nutrients. In addition to the vital function, mycorrhizas in citrus display other roles in soils and plants. Most AMF species usually significantly increase plant growth and fruit quality of citrus plants, but occasionally inhibit or did not impact plant growth. The inoculation with AMF obviously improved root system architecture of citrus, thereby conferring greater ability of the host plant to obtain soil resources. Mycorrhizas can develop an extensive common mycorrhizal network to colonize neighbouring citrus or other plants for underground communication. AMF release a special glycoprotein, glomalin, into the soils, which can improve soil structure and contribute soil carbon pools, thus, providing better soil fertility and soil physical-chemical traits. Mycorrhizas enhance tolerance of citrus plants to drought stress, salt stress, high temperature but not low temperature, flooding, elevated [CO2], diseases, and insect pests in terms of various physiological and molecular approaches. Based on the mycorrhizal functionings, citrus production will consider mycorrhizal management of citrus orchard and new perspectives are also outlined.