Applications of biotechnology to citrus improvement in Spain

Abstract

Citrus are subject to many biotic and abiotic stresses and markets are continuously requiring fruits of higher quality. These pose important problems in most citrus growing areas that can only be solved with the establishment of citrus improvement programs to recover new and healthy genotypes to be used as rootstocks and varieties. Success of traditional citrus breeding strategies is limited by the peculiar genetic and reproductive characteristics of citrus. Biotechnology offers different approaches that can overcome many of these limitations. In this paper the following technologies used in Spain are reviewed: a) Shoot tip grafting in vitro. It is used worldwide to recover plants free of all known citrus pathogens, and already hundreds of millions of trees originated in this technique have been planted in the field; b) Embryo rescue. It is used in large programs to recover triploid seedless hybrid varieties from aborted seeds from 2n x 4n and 2n x 2n crosses; c) Protoplast fusion. It allows the production of allotetraploid hybrids among sexually compatible and incompatible parents to be used as rootstocks or as parentals for interploid breeding. Fusions between diploid and haploid cell lines are also used to produce triploid hybrids. d) Genetic transformation. Efficient protocols for transformation of several genotypes have been developed and introduction in citrus of genes of potential agronomical interest has been accomplished.