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

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

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

Application of Recent Biotechnologies to Prunus Tree Crop Genetic Improvement

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 en Prunus. 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 transgénica

Resistance to aspergillus flavus and aspergillus parasiticus in almond advanced selections and cultivars and its interaction with the aflatoxin biocontrol strategy

Open Access Journal; Published online: 05 Feb 2022Aflatoxin contamination of almond kernels, caused by Aspergillus flavus and A. parasiticus, is a severe concern for growers because of its high toxicity. In California, the global leader of almond production, aflatoxin can be managed by applying the biological control strain AF36 of A. flavus and selecting resistant cultivars. Here, we classified the almond genotypes by K-Means cluster analysis into three groups (susceptible [S], moderately susceptible [MS], or resistant [R]) based on aflatoxin content of inoculated kernels. The protective effects of the shell and seedcoat in preventing aflatoxin contamination were also examined. The presence of intact shells reduced aflatoxin contamination >100-fold. The seedcoat provided a layer of protection but not complete protection. In kernel inoculation assays, none of the studied almond genotypes showed a total resistance to the pathogen. However, nine traditional cultivars and four advanced selections were classified as R. Because these advanced selections contained germplasm derived from peach, we compared the kernel resistance of three peach cultivars to that shown by kernels of an R (Sonora) and an S (Carmel) almond cultivar and five pistachio cultivars. Overall, peach kernels were significantly more resistant to the pathogen than almond kernels, which were more resistant than pistachio kernels. Finally, we studied the combined effect of the cultivar resistance and the biocontrol strain AF36 in limiting aflatoxin contamination. For this, we coinoculated almond kernels of R Sonora and S Carmel with AF36 72 h before or 48 h after inoculating with an aflatoxin-producing strain of A. flavus. The percentage of aflatoxin reduction by AF36 strain was greater in kernels of Carmel (98%) than in those of Sonora (83%). Cultivar resistance also affected the kernel colonization by the biological control strain. AF36 strain limited aflatoxin contamination in almond kernels even when applied 48 h after the aflatoxin-producing strain. Our results show that biocontrol combined with the use of cultivars with resistance to aflatoxin contamination can result in a more robust protection strategy than the use of either practice in isolation

QTL mapping of pomological traits in peach and related species breeding germplasm

Peach is an economically important fruit tree crop that exhibits high phenotypic variability yet suffers from diversity-limited gene pool. Genetic introgression of novel alleles from related species is being pursued to expand genetic diversity. This process is, however, challenging and requires the incorporation of innovative genomic and statistical tools to facilitate efficient transfer of these exotic alleles across the multiple generations required for introgression. In this study, pedigree-based analysis (PBA) in a Bayesian QTL mapping framework was applied to a diverse peach pedigree introgressed with almond and other related Prunus species. The aim was to investigate the genetic control of eight commercially important fruit productivity and fruit quality traits over two subsequent years. Fifty-two QTLs with at least positive evidence explaining up to 98 % of the phenotypic variance across all trait/year combinations were mapped separately per trait and year. Several QTLs exhibited variable association with traits between years. By using the peach genome sequence as a reference, the intrachromosomal positions for several QTLs were shown to differ from those previously reported in peach. The inclusion of introgressed germplasm and the explicit declaration of the genetic structure of the pedigree as covariate in PBA enhanced the mapping and interpretation of QTLs. This study serves as a model study for PBA in a diverse peach breeding program, and the results highlight the ability of this strategy to identify genomic resources for direct utilization in marker-assisted breeding

Advanced in Rootstock Breeding of Nut Trees: Objectives and Strategies

The production and consumption of nuts are increasing in the world due to strong economic returns and the nutritional value of their products. With the increasing role and importance given to nuts (i.e., walnuts, hazelnut, pistachio, pecan, almond) in a balanced and healthy diet and in the prevention of various diseases, breeding of the nuts species has also been stepped up. Most recent fruit breeding programs have focused on scion genetic improvement. However, the use of locally adapted grafted rootstocks also enhanced the productivity and quality of tree fruit crops. Grafting is an ancient horticultural practice use in nut crops to manipulate scion phenotype and productivity and overcome biotic and abiotic stresses. There are complex rootstock breeding objectives and physiological and molecular aspects of rootstock–scion interactions in nut crops. In this review, we provide an overview of these, considering the mechanisms involved in nutrient and water uptake, regulation of phytohormones, and rootstock influences on the scion molecular processes, including long-distance gene silencing and trans-grafting. Understanding the mechanisms resulting from rootstock × scion × environmental interactions will contribute to developing new rootstocks with resilience in the face of climate change, but also of the multitude of diseases and pests and of the possible increase of their aggressiveness. They will also have to offer the premises of economic production, respectively yield and the quality, according to multiple destinations of nuts in the current consumption and food industry, but also the increasing exigencies of the consumer market and the profile industry.Publishe