Application of Recent Biotechnologies to Prunus Tree Crop Genetic Improvement.

Promising tools for Prunus breeding include germplasm introgression, molecular marker development and improved propagation and gene transfer techniques. In germplasm introgression, the introduction of genes from related Prunus species conferring agronomically valuable traits such as self-compatibility, improved growth habit, drought resistance, and higher kernel quality are being pursued. The analyses of twin seeds (two embryos within the same seedcoat) are facilitating genetic and cytogenetic studies. Useful propagation methods include in-vitro techniques for the evaluation of plant material, and in-vivo micrograft techniques that allow the early propagation of high-risk genotypes. In addition, plant growth under controlled environments, including the induction of an artificial rest period using cold chambers, provides a useful strategy for obtaining vigorously growing plants all the year round. Molecular markers have also become an essential tool in Prunus genetic improvement studies. Different types of molecular markers, including isoenzymes, RFLPs, RAPDs, AFLPs and SSRs, have been employed for the genetic characterization of germplasm, the establishment of genetic relationships between cultivars and species, and the construction of genetic maps. Methodologies for the analysis of marker-assisted selection include the use of mapping populations segregating for desired characters and bulk segregant analysis. Genetic engineering offers a resolution to problems encountered by traditional Prunus breeding programs including long juvenility period and large space requirements for breeding populations. A number of genetically modified Prunus cultivars have been obtained using different gene transfer methods. Additional research work is still required to fully develop the next generation of gene vectors and transgenic plants.  La utilización de nuevo germoplasma, el desarrollo de marcadores moleculares, la utilización de técnicas alternativas de propagación y la transferencia de genes, se cuentan entre las novedosas herramientas aplicables al mejoramiento de Prunus. En la utilización de nuevo germoplasma, se persigue la introducción de genes de especies de Prunus silvestres que confieren caracteres agronómicamente valiosos tales como la autocompatibilidad, el hábito de crecimiento mejorado, la resistencia a la sequía, y la mejora de la calidad del fruto o semilla. Por otro lado, los estudios con semillas poliembriónicas (dos embriones dentro de una misma cubierta seminal) pueden facilitar los estudios genéticos y citogenéticos de estas especies. Entre los métodos de propagación alternativos se encuentran las técnicas in vitro para la evaluación del material vegetal, y las técnicas de microinjerto in vivo que permiten la propagación temprana de genotipos de alto riesgo. Además, el cultivo de los Prunus bajo condiciones controladas en invernadero, incluyendo la inducción de un período de reposo artificial mediante el uso de tratamientos en cámara fría, provee una estrategia útil para obtener plantas de crecimiento vigoroso durante todo el año. Los marcadores moleculares también se han constituido en una herramienta esencial para los estudios de mejoramiento genético enPrunus. Se han utilizado distintas clases de marcadores moleculares, incluyendo isoenzimas, RFLPs, RAPDs, AFLPs y SSRs, para la caracterización genética del germoplasma, el establecimiento de relaciones génicas entre cultivares y especies, y la construcción de mapas genéticos. Las metodologías para el análisis de la selección asistida por marcadores incluye el uso del mapeo de poblaciones segregantes para caracteres deseables y el análisis de grupos segregantes. La ingeniería genética ofrece una resolución a problemas que enfrentan los programas de mejoramiento tradicionales de Prunus, incluyendo un período juvenil prolongado y requerimientos de grandes espacios para las poblaciones en cruzamiento. Se ha obtenido un número apreciable de cultivares de Prunus genéticamente modificados utilizando diferentes métodos de transferencia de genes. Sin embargo, se requiere aún trabajo de investigación adicional para desarrollar completamente la próxima generación de vectores de genes y plantas transgénicas

Physical Fruit Traits in Moroccan Almond Seedlings: Quality Aspects and Post-Harvest Uses

The physical traits of local almond populations from Morocco were studied to characterize their genetic resources and to evaluate the possibility of their commercial valorization. Nut weight ranged between 1.15 and 7.39 g, and kernel weight between 0.54 and 1.85 g, but most accessions were characterized by small kernels, pronounced wrinkles, and double kernels. Although the physical quality of the kernels of these populations was low, they show the possibility of some specialized uses, which could improve their marketable value. The genotypes with favorable values could be incorporated into an almond breeding program as parents to increase the kernel quality.Publishe

Pedigree analysis of 220 almond genotypes reveals two world mainstream breeding lines based on only three different cultivars

Loss of genetic variability is an increasing challenge in tree breeding programs due to the repeated use of a reduced number of founder genotypes. However, in almond, little is known about the genetic variability in current breeding stocks, although several cases of inbreeding depression have been reported. To gain insights into the genetic structure in modern breeding programs worldwide, marker-verified pedigree data of 220 almond cultivars and breeding selections were analyzed. Inbreeding coefficients, pairwise relatedness, and genetic contribution were calculated for these genotypes. The results reveal two mainstream breeding lines based on three cultivars: “Tuono”, “Cristomorto”, and “Nonpareil”. Descendants from “Tuono” or “Cristomorto” number 76 (sharing 34 descendants), while “Nonpareil” has 71 descendants. The mean inbreeding coefficient of the analyzed genotypes was 0.041, with 14 genotypes presenting a high inbreeding coefficient, over 0.250. Breeding programs from France, the USA, and Spain showed inbreeding coefficients of 0.075, 0.070, and 0.037, respectively. According to their genetic contribution, modern cultivars from Israel, France, the USA, Spain, and Australia trace back to a maximum of six main founding genotypes. Among the group of 65 genotypes carrying the Sf allele for self-compatibility, the mean relatedness coefficient was 0.125, with “Tuono” as the main founding genotype (24.7% of total genetic contribution). The results broaden our understanding about the tendencies followed in almond breeding over the last 50 years and will have a large impact into breeding decision-making process worldwide. Increasing current genetic variability is required in almond breeding programs to assure genetic gain and continuing breeding progress

Caracterización de embriones múltiples en almendro

Multiple embryos within the same tegument occur spontaneously in certain almond [Prunus dulcis (Mill.) D.A. Webb]cultivars including Nonpareil and Mission. Seedlings from the same polyembryonic seed are frequently viable, thoughoften one of the seedlings shows weak growth and develops poorly. These dwarf seedlings have been characterised in aprevious work as haploid. In this work, we have characterised 450 seedlings from polyembryonic seeds of the Californiancultivar Nonpareil, and 100 seedlings from polyembryonic seeds of the Spanish selections D97396 and D97407,including their germination and later growth. Isozyme and Simple Sequence Repeat markers were used to geneticallyanalyse seedling genetic structure. In addition, individual mitotic karyotypes were determined following staining of roottips. The percentage of twin embryos showing aberrant growth was approximately 25% with mortality rates of about 90%.Results suggested the sexual origin of both embryos. Seedlings from the same seed are genetically identical with a similargrowth, though often one of the seedlings from the secondary embryo loses part of the genomic contents and becomesan aneuploid plant and showed a weak development. The use of this material in almond breeding is also discussed.La aparición de embriones múltiples dentro del mismo tegumento es un fenómeno espontáneo que ocurre en semillas de algunas variedades de almendro [Prunus dulcis (Mill.) D.A. Webb] como "Nonpareil" o "Mission". Las plántulas procedentes de estas semillas poliembriónicas son viables, aunque a menudo muestran un crecimiento más debil y retrasado. Estas plántulas enanas han sido caracterizadas como haploides en trabajos previos. En este trabajo hemos estudiado 450 plántulas procedentes de semillas poliembriónicas de la variedad californiana "Nonpareil" y 100 plántulas procedentes de semillas poliembriónicas de las selecciones españolas "D97396" y "D97407", observando su germinación y posterior crecimiento. Estas plántulas han sido caracterizadas molecularmente mediante marcadores isoenzimáticos y microsatélites (...

Periclinal chimeras as a strategy for cultivar development

This review summarizes current knowledge on the synthesis, characterization and utilization of interspecific chimeras. Results are also generally relevant to intraspecies chimeras as well. Plant chimera is a type of mosaic in which genetically different tissues develop side by side. Essential components targeted for improvement include chimera induction, selection efficiency, histogen identification, characterization, and stabilization. This chapter reviews the interspecific chimeras with emphasis on species of the Brassicaceae, Euphorbiaceae, Rutaceae, and Solanaceae. The recovery of periclinal chimeras in which tissue from different interspecific or intergeneric origins is combined in a single clonal plant, has potential for crop improvement