Development of doubled haploids, chromosome doubling and CRISPR/Cas9 techniques in melon for the next generation of breeding

Abstract

The general aim of this PhD thesis was to study, develop and apply different breeding techniques in melon species in order to produce new commercial cultivars. The three specific objectives of this thesis are:

1. To study and evaluate the commercial value and the parthenogenetic capacity of seven genotypes of C. melo var. Inodorus “Piel de Sapo” type to obtain DH lines which might be further used as parental lines for commercial hybrid F1 seed production. The parthenogenetic generation of DHs from the seven genotypes was evaluated and optimized through the analysis and description of the different steps of the process, assaying: three haploid embryo rescue protocols, previously described in the literature; three chromosome doubling methods; and, a new cytometry flow method for evaluating the ploidy-level.

2. To develop the applicability of CRISPR/Cas9 system in melon by performing a gene knockout of the melon phytoene desaturase gene (CmPDS) in protoplasts and plants.

3. To study and highlight the current methodology in major crops for DH production, the availability of chromosome-doubling methods to obtain DH lines, and the opportunities for HI-mediated genome-editing systems in DH technology. Specifically, the focus was put on haploid inducer-mediated genome-editing systems in cucurbit species to give new insights, opportunities and challenges that may be valuable for developing this technique in cucurbits and other species.