Genomic Instability in Somatic Hybridization between Poncirus and Citrus Species Aiming to Create New Rootstocks

Dominique Dambier,Pascal Barantin,Patrick Ollitrault,Raphaël Morillon,Gabriel Boulard,Pierre Mournet,Aude Perdereau,Gilles Costantino

doi:10.3390/agriculture12020134

Abstract

Rootstocks are an important component for citrus adaptation to increasing biotic and abiotic stresses resulting from global climate change. There is a strong complementarity between Citrus species, which adapt to abiotic stresses, and Poncirus trifoliata and its intergeneric hybrids, which exhibit resistances or tolerances to major diseases and pests. Thus, symmetrical somatic hybridization between complementary diploid rootstocks of these two genera appears to be an efficient way to develop new tetraploid rootstocks in order to address the new challenges of the citrus industry. New intergeneric somatic hybrids were obtained by electrofusion between protoplasts of Citrus and P. trifoliata hybrids. Extensive characterization of the nuclear and cytoplasmic genomes was performed by genotyping-by-sequencing (GBS) analysis. This revealed diploid cybrids and nuclear somatic hybrids. Mitochondrial genomes were mostly inherited from the callus parent, but homologous recombination events were observed for one parental combination. Chloroplasts exhibited random uniparental inheritance. GBS revealed local chromosomal instabilities for all nuclear somatic hybrids and whole chromosome eliminations for two hybrids. However, at the whole genome level, symmetrical addition of the nuclear genomes of both parents was predominant and all somatic hybrids displayed at least one trifoliate orange haplotype throughout the genome.

Highlights

Global climate change and environmental instability over seasons and years are significantly affecting agricultural production, of woody crops [1]
We focus on somatic hybridization between Citrus species and P. trifoliata or F1 sexual intergeneric hybrids between Citrus and Poncirus, such as citranges, citrumelos, and citrandarins
Leaf protoplasts were isolated for the Winter Haven citrumelo, the Carrizo citrange, and a citrumelo 4475 cybrid with Chios mandarin mitochondria [18], while embryogenic callus protoplasts were obtained for Cleopatra mandarin and Shamouti sweet orange

Summary

Introduction

Global climate change and environmental instability over seasons and years are significantly affecting agricultural production, of woody crops [1]. × aurantium L.) was the most widely used rootstock until the emergence of a second major disease outbreak caused by CTV that killed millions of trees grafted onto sour orange worldwide in the mid-20th century. This second crisis drove a major diversification of the genetic base of citrus rootstocks, the use of trifoliate orange (Poncirus trifoliata (L.) Raf.), due to its immunity to CTV [6] and its good levels of resistance to phytophthora and nematodes. Some authors have described various levels of resistance to HLB [7,8,9,10] and its vector Diaphorina citri [11] in P. trifoliata

Methods

Results

Discussion

Conclusion