Herramientas biotecnológicas aplicadas a la mejora genética de melocotón y nectarina

Abstract

The world population is currently growing in a global food crisis framework, in which science has to rise to the occasion. In the last decades, plant science has offered alternatives to the world, including a deep understanding and improvement of crop quality. Several techniques have been developed in order to increase production or quality by means of adapting horticulture to environmental conditions. Plant breeders have been searching for crop improvements in terms of solutions for different problems, namely diseases, production or postharvest problems. But breeders have also varied objectives such as adaptation of new cultivars to growing areas, disease resistance, ripening fruit, high productivity and organoleptic quality. However, the results obtained in classical breeding programs are limited by a methodology that has not been updated for decades: pollen collection, hybridization, crop harvest, seed germination, and transplanting to the field. Other important factor is seeds containing immature embryos. They are due to a short period between blooming and ripening that leads to low percentages of germination. Immature embryo rescue techniques provide an alternative means to recover seeds from early ripening fruit, which usually fails to completely develop in vivo. But also, fruit breeding programs are facing two limiting factors: long reproductive cycles and long juvenile phases. Thus, the combination of all of them rises the average release time of a new cultivar to a 10-year range. Peach (Prunus persica L. Batsch) is one of the major fruits in the world. Thus, the economic value of this crop is one of the bases of agriculture in Europe. Currently, after decades of breeding, breeding still requires too much time obtaining peach fruits with interesting characteristics because traditional techniques are being used and the genetic basis of economically important traits are unknown. But also, in spite of the presence of some 70 peach breeding programs, peach breeding programs have failed to stabilize certain characters after many cycles of selection. This is the case of resistance to Plum Pox Virus (PPV), widely known as Sharka, a disease with high capacity for viral infection, which affects the productivity and fruit quality of Prunus species. Biotechnology has been presented as a tool to overcome the limitations of classical improvement, through the incorporation of desirable genes that either confer resistance to diseases or boost the beneficial properties of some species. In this sense, genetic transformation is an important tool that can be used in different ways. This technique is very well known as an application to provide protection to crops against certain diseases or insect actions. However, as the genome of different plant species has been sequenced, genetic transformation has played a major role in the elucidation of gene function. To efficiently harness genetic transformation technology, an efficient plant regeneration protocol from plant cells is required. Although in some species this phenomenon occurs almost spontaneously, in others such as woody plants it is quite difficult to achieve. Peach is a particularly recalcitrant species in this sense, in which only some authors have reported somatic regeneration protocols, and in most cases from zygotic tissue. The drawback of using seed-derived material for genetic transformation techniques are that each genotype is unique and not a clone of the parent. The development of plant regeneration protocols from mature tissues is important for the modification of desirable commercial cultivars that have been selected because of economic potential. Since cultivars are typically heterozygous, the seed they produce segregate and the desirable traits may not be present in the progeny that they produce. This research focuses in the development of protocols for both in vitro rescue of embryos and somatic regeneration in peach. On one hand, the searching for a general and improved protocol for embryo rescue in peach can provide a supplementary tool for the peach and nectarine breeding program developed in IMIDA. On the other hand, developing a series of studies that lead to achieve an efficient protocol for plant regeneration will contribute to take a step forward in genetic transformation in peach. Preliminary field studies of genetic transformation are also included in this present dissertation.