Genetic improvement of Citrus for disease resistance

Progress in the genetic improvement of Citrus species was reviewed. Tools used for the genetic improvement of Citrus were categorised as conventional (introduction, selection and hybridisation) and non-conventional methods (mutation, somatic cell hybridisation and genetic engineering) of improvement. Genes linked with the disease resistance were characterised and tagged through molecular marker techniques such as Sequenced Characterised Amplified Region and Cleaved Amplified Polymorphic Sequences. Disease resistance genes showed both monogenic and polygenic inheritance. Conventional methods for disease resistance improvement of Citrus were bottleneck due to inadequate and lengthy breeding procedures. However, non-conventional methods, such as mutation breeding and protoplast fusion, have been routinely utilised for the production of disease resistant germplasm while novel genes from variable sources were used to transform Citrus species to induce resistance against diseases. These non-conventional techniques have been shown to overcome the disadvantages of conventional breeding procedures and could be regarded as rapid methods of genetic improvement as well as helpful to overcome the interspecies barrier.