Somatic cybrid production via protoplast fusion for citrus improvement

• More than forty leaf-parent-type cybrids or putative cybrids were produced in citrus.
• Somatic cybridization aiming to produce male sterile and seedless citrus cybrids was detailed.
• Agronomic performance and omics-based studies of some selected cybrids were reviewed.

Somatic hybridization holds great potential in citrus improvement by circumventing several biological barriers such as nucellar polyembryony, long juvenility and pollen/ovule sterility. To date more than 300 intergeneric and interspecific citrus somatic hybrids have been produced by standard symmetric fusion; among which, more than forty parental combinations produced leaf-parent-type cybrids or putative cybrids. Herein somatic cybrid production by protoplast fusion aiming to produce citrus cybrids with male sterile cytoplasm being transferred simply via symmetric fusion is detailed including methods to produce cybrids, possible mechanism and factors involved in cybrid production via symmetric fusion, strategy of targeted cybrid production for potential seedlessness, and agronomic performance and omics-based studies of some selected cybrids. This review provides the most comprehensive and updated information concerning citrus cybrid production over the past 20 years.