New Plant Breeding Techniques in Citrus for the Improvement of Important Agronomic Traits. A Review

Abstract

New plant breeding techniques (NPBTs) aim to overcome traditional breeding limits for fruit tree species, in order to obtain new varieties with improved organoleptic traits and resistance to biotic and abiotic stress, and to maintain fruit quality achieved over centuries by (clonal) selection. Knowledge on the gene(s) controlling a specific trait is essential for the use of NPBTs, such as genome editing and cisgenesis. In the framework of the international scientific community working on fruit tree species, including citrus, NPBTs have mainly been applied to address pathogen threats. Citrus could take advantage of NPBTs because of its complex species biology (seedlessness, apomixis, high heterozygosity, and long juvenility phase) and aptitude for in vitro manipulation. To our knowledge, genome editing in citrus via transgenesis has successful for induced resistance to Citrus bacterial canker in sweet orange and grapefruit using the resistance gene CsLOB1. In the future, NPBTs will also be used to improve fruit traits, making them healthier. The regeneration of plants following the application of NPBTs is a bottleneck, making it necessary to optimize the efficiency of current protocols. The strengths and weaknesses of using explants from young in vitro plantlets, and from mature plants, will be discussed. Other major issues addressed in this review are related to the requirement for marker-free systems and shortening the long juvenility phase. This review aims to summarize methods and approaches available in the literature that are suitable to citrus, focusing on the principles observed before the use of NPBTs.

SuperSour: A New Strategy for Breeding Superior Citrus Rootstocks

“…Over the last 35 years, research efforts to develop improved citrus rootstocks have expanded at many institutions to include new methodologies ( Salonia et al, 2020 ), including ploidy manipulations, somatic hybridization, genetic transformation, and genome editing. Selections of rootstock clones with a doubling of chromosomes, or autotetraploids, can often be visually identified among groups of seedlings and have received interest for more than 80 years ( Lapin, 1937 ; Russo and Torrisi, 1951 ; Barrett and Hutchison, 1978 ; Bowman et al, 1991 ; Ollitrault et al, 2020 ).…”

De Novo Transcriptome Sequencing of Rough Lemon Leaves (Citrus jambhiri Lush.) in Response to Plenodomus tracheiphilus Infection

“…In this context, next-generation high-throughput sequencing techniques have become an increasingly useful tool for exploring whole plant genomes, providing a means for analyzing plant molecular regulatory mechanisms in specific abiotic and biotic stress conditions. The identification of candidate genes is a prerequisite for the application of new genome editing techniques by which targeted genetic modifications can lead to the introduction of precise changes directly into the genome of commercial varieties, offering an alternative to traditional methods of genetic improvement [ 19 , 20 , 21 ]. Different authors in the last years conducted transcriptomic analysis to better understand Citrus plants response to biotic stress caused by pathogens [ 22 , 23 , 24 , 25 , 26 , 27 ].…”

Overexpression of CsSAMT in Citrus sinensis Induces Defense Response and Increases Resistance to Xanthomonas citri subsp. citri

“…Currently, copper-based chemicals are the main compounds used to control citrus canker; however, their excessive use leads to environmental issues, plant stress, and bacterial resistance ( Lamichhane et al, 2018 ; Behlau et al, 2020 ; Heydarpanah et al, 2020 ). To overcome these problems, biotechnology-based approaches have shown potential to increase plant resistance against citrus canker in a sustainable way ( Caserta et al, 2020 ; Salonia et al, 2020 ; Soares et al, 2020 ).…”