Parthenogenic Haploids in Melon: Generation and Molecular Characterization of a Doubled Haploid Line Population

Abstract

<jats:p>Melon (<jats:italic>Cucumis melo</jats:italic>) is one of the principal vegetable crops for fresh market, for which a large number of breeding programs, oriented to generate inbred pure lines and hybrids, is established worldwide. The process to obtain and select these lines has been highly accelerated by the use of biotechnological techniques such as the generation of doubled haploid line (DHL) populations and molecular markers. Moreover, the use of DHLs in genetic studies is a useful tool because of their complete homozygosity and the permanent availability of plant material perpetuated by seed. In this work, the parthenogenetic response of 17 melon genotypes and the F<jats:sub>1</jats:sub> hybrid PI 161375 × Spanish cultivar Piel de Sapo (PS) was studied considering three stages along the in vitro DHL generation process. The response of the analyzed melon cultivars was heterogeneous through the DHL generation with different limiting steps for each genotype. The response of the PI 161375 × PS hybrid was more similar to the male (PS) than the female parent (PI 161375), although the response of the maternal genotype was higher for some stages. This points to the important role of alleles from both parents in the different steps of the DHL generation process, and it could explain the identification of six genomic regions with distorted allelic segregation skewed toward PS or PI 161375. This hybrid was used to generate a population of 109 DHLs, the gametophytic origin of which was confirmed by flow cytometry and molecular markers.</jats:p>

A consensus linkage map for molecular markers and Quantitative Trait Loci associated with economically important traits in melon (Cucumis meloL.)

“…No significant segregation distortion was detected in the other maps used herein (data not shown). The relatively high number of genomic regions with skewed segregation detected in the DHL-based map reinforces the hypothesis that such distortion likely originated from unintentional selection during the in vitro line development process [33]. The low number of genomic regions showing skewed segregation in most melon maps contrasts with that reported in other crops such as lettuce [2], red clover [4], sorghum [34], and tomato [35].…”

In situ Parthenogenetic Doubled Haploid Production in Melon “Piel de Sapo” for Breeding Purposes

“…In this parthenogenetic study, the genotypic response of seven genotypes of melon "Piel de Sapo" type differed for: fruit set when pollinated with irradiated pollen; parthenogenetic embryo induction; haploid embryo germination; chromosome doubling; and, fruit set of DH lines. The parthenogenetic ability of melon "Piel de Sapo" germplasm used was lower than other genotypes such as chinensis, cantalupensis or inodorus (Lotfi et al, 2003;Lim and Earle, 2008;Gonzalo et al, 2011).…”

“…Pollen sensitivity to irradiation its attributed to radio-resistance, and the viability of pollen is decreased along with the irradiation exposure. Previous reports in melon (Lim and Earle, 2008;Gonzalo et al, 2011;Godbole and Murthy, 2012) used an irradiation exposure of 250 Gy, therefore, prior to the experiment, this dose was evaluated based on fruit set and pollen germination assays (data not shown). Moreover, during pollination with irradiated pollen, fruit set was observed to be dependent on: the time of the year, being August the period when more fruit set; the stage of donor plants, at the beginning of flowering and the end of the greenhouse culture fruit set was low; and, the weather, cloudy pollination days resulted in less fruits than shinny days.…”

“…Nevertheless, in situ parthenogenesis in cucurbits and specifically, in melon, has many bottlenecks that reduces its efficiency in each step of the process. Melon parthenogenesis has a high genotypic dependency and methodological issues that impede the efficient production of DHs such as: low levels of female flowers developed once pollinated with irradiated pollen; low production of haploid embryos; difficulty to detect seeds containing haploid embryos; low germination of haploid embryos in vitro; high mortality of germinated embryos and growing plantlets; very low or null spontaneous chromosome duplication; difficulty to induce chromosome doubling in haploid plants due to a high mortality and hyperhidricity; high ratio of haploid and mixoploid plants; low pollen germination levels of chromosome doubled plants which trigger a decrease of fruit set and seed recovery; and, low DH seed germination Earle, 2008, 2009;Gonzalo et al, 2011;Dong et al, 2016).…”

“…Colchicine has been the most used antimitotic in melon for chromosome doubling, either via immersion of in vitro shoot tips or nodular explants, or via immersion of in vivo shoot tips. Chromosome doubling rate can range from 0 to 90% depending on the genotype (Yetisir and Sari, 2003;Lim and Earle, 2008;Gonzalo et al, 2011;Solmaz et al, 2011).…”