There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Plant population Genetics, Breeding and Genetic Resources

Persian or English walnut (Juglans regia L.), the walnut species cultivated for nut production, is one of the oldest food sources known. Persian walnuts, native to the mountain valleys of Central Asia, are grown worldwide in temperate areas. World production exceeds three million tons since 2012, mostly provided by China, the USA, and Iran. Despite very ancient culture of walnut species (Juglans spp.), breeding actually started in the twentieth century. Using a range of methodologies, from morphological markers to the most recent advances in genome analysis, many genetic studies of walnut have been conducted during the past 30 years, including examination of diversity, determination of relationships within or among germplasm collections and populations, phylogenetic and origin elucidation, genetic map construction, and biotic or abiotic stress investigations. The genetic improvement of walnut has undergone great evolution. The producing countries of the Middle East have widely studied morphological characteristics of walnut. The USA and France, for example, are behind important cultivar releases such as “Chandler” and “Franquette.” Finally, genomics represents a major breakthrough in walnut improvement, in particular by recent sequencing of both chloroplast and nuclear genomes. This review summarizes worldwide molecular and “omics” studies and gives an overview of the main walnut breeding programs.

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Walnut: past and future of genetic improvement

One of the main disorders that widely limit fruit quality and quantity is fruit cracking or splitting that is observed on the fruit skin and flesh in the preharvest phase. Besides, cracking can occur during postharvest in some fruits, mostly attributable to the environmental conditions of storage. Value of cracked fruits is reduced and these fruits are not marketable because of the poor fruit quality. Many fruits such as apple, sweet cherry, grape, plum, pomegranate, grape, persimmon, litchi, avocado, pistachio, citrus, banana as well as tomato can crack or split. There are many factors that influence fruit cracking. In this work, genetic, morphological, environmental and physiological aspects of fruit cracking are reviewed. Under the same environmental conditions, fruits from different cultivars show differences in cracking susceptibility. Some correlations have been observed between susceptibility of fruit cracking and some fruit traits (fruit shape, fruit size, fruit firmness; anatomy and strength of the fruit skin, stomata in fruit skin, cuticular properties, osmotic concentration, water capacity of the fruit pulp and growth stage of the fruit). Also, orchard management (such as irrigation and nutrition) and environmental condition (such as temperature, wind and light) can influence fruit cracking. Besides, fruit cracking is quantitative trait and is controlled by several genes. The best way to reduce fruit cracking at present would be a suitable orchard management that takes into account and try to minimize stress of the water, nutrition and physiological factors that contribute to fruit cracking. Also, the most resistant cultivars to fruit cracking that have desirable fruit quality can be selected for cultivation.

Physiological and genetic factors influencing fruit cracking

During the evolution of the eukaryotic cell, plastids and mitochondria arose from an endosymbiotic process, which determined the presence of three genetic compartments into the incipient plant cell. After that, these three genetic materials from host and symbiont suffered several rearrangements, bringing on a complex interaction between nuclear and organellar gene products. Nowadays, plastids harbor a small genome with ~130 genes in a 100-220 kb sequence in higher plants. Plastid genes are mostly highly conserved between plant species, being useful for phylogenetic analysis in higher taxa. However, intergenic spacers have a relatively higher mutation rate and are important markers to study genetic diversity and divergence within natural plant populations. The predominant uniparental inheritance of plastids is like a highly desirable feature for phylogeny studies. Moreover, the gene content and genome rearrangements are efficient tools to capture and understand evolutionary events between different plant species. Currently, genetic engineering of the plastid genome (plastome) offers a number of attractive advantages as high-level of foreign protein expression, marker-gene excision, gene expression in operon and transgene containment because of maternal inheritance of plastid genome in most crops. Therefore, plastid genome can be used for adding new characteristics related to synthesis of metabolic compounds, biopharmaceutical and tolerance to biotic and abiotic stresses. Here, we describe the importance and applications of plastid genome as tools for genetic and evolutionary studies, and plastid transformation focusing on increasing the performance of horticultural species in the field.

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Plastid genomics in horticultural species: importance and applications for plant population genetics, evolution, and biotechnology.

Knowledge of relationships among the cultivated and wild species of Cerasus, a subgenus of Prunus L., is important for recognizing gene pools, identifying pitfalls in germplasm collections and developing effective conservation and management strategies. In this study, morphological characterization of wild Cerasus subgenus species naturally growing in Iran, including P. avium L. (mazzard), P. mahaleb L., P. brachypetala Boiss., P. incana Pall., P. yazdiana Mozaff., P. microcarpa Boiss. subsp. microcarpa, P. microcarpa Boiss. subsp. diffusa and P. pseudoprostrata Pojark. and three commercial species, sweet cherry (P. avium L.), sour cherry (P. cerasus L.) and duke cherry (P. × gondouinii Rehd.) was investigated. Twenty-nine variables were recorded in 95 accessions of these species to detect similarities among them. All studied characteristics were showing a high degree of variability, but it was highly pronounced for plant height, leaf characters especially for dimensions and pubescence as well as for petiole and peduncle length. The majority of significant correlation coefficients were found in the characteristics representing plant size and growth habit with leaf size. Principal component analysis was performed for phenotypical diversity determination and grouping of species. Characters with high discriminating values were those related to growth habit, height, compactness, trunk diameter, leaf dimensions, petiole length, leaf tip and serration, flower color, peduncle length, fruit shape and stone shape. Based on the cluster analysis, species included in two main clusters, first those with large structure (sweet, sour and duke cherries, mazzard and mahaleb), second the other species with small structure which might be potentially suitable for rootstock breeding programs. Scatter plot using two first factors also confirmed the grouping by cluster analysis. The conservation of the highly diverse native populations of Iranian wild Cerasus species is recommended.

Multivariate analysis of Prunus subgen. Cerasus germplasm in Iran using morphological variables

In this research, morphological characterization of wild Prunus scoparia species, naturally growing in Iran, was investigated. Twenty-one variables along flowering and ripening date were recorded in 150 accessions of this species to detect their phenotypic variation. All studied characteristics were showing a high degree of variability, but it was highly pronounced for secondary shoot number, leaf area and shape, growth habit, fruit exocarp color, nut shape, pubescence on fruit, canopy size and trunk diameter. The majority of significant correlation coefficients were found in the characteristics representing tree and nut sizes with leaf size. Principal component analysis was performed for phenotypical diversity determination and grouping of species. Characters with high discriminating values were those related to tree height, growth habit, canopy size and kernel weight. Based on the UPGMA cluster analysis, accessions were placed in two main clusters. The first main cluster was divided into five subclusters with high variability within and between populations, while the second cluster contained 11 accessions of Estahban region. Current findings supported these opportunities since the phenotypic variability in Iranian wild P. scoparia species has been found to be very high, suggesting an extensive genetic diversity available to almond cultivar and rootstock development programs. The wide adaptation of this species indicates its potential as resources for resistance to abiotic and biotic stresses such as drought and spring frost. The conservation of the highly diverse native populations of Iranian wild P. scoparia species is recommended.

Morphological characterization of Prunus scoparia using multivariate analysis

Genetic variability and structure of Quercus brantii assessed by ISSR, IRAP and SCoT markers.

Sweet cherry (Prunus avium L.), a member of Rosaceae family, is an economically important fruit of the temperate zone. In Iran, various sweet cherry genotypes are grown in different areas. For estimation of genetic diversity, 23 RAPD decamer primers data as well as 23 morphological traits were used on 39 sweet cherry cultivars and genotypes, 28 of Iranian and 11 of foreign origin. Random Amplified Polymorphic DNA (RAPD) data was used for clustering of genotypes using UPGMA method. Based on the results, in some cases, clustering of genotypes by RAPD data was in agreement with morphological data; however, the correlation between the two sets of data was not significant (r = 0.2). The coephenitic coefficients between genotypes varied from 0.43 to 0.83 and the value of calculated polymorphism was 81.7 percent, indicating the presence of a high variation between the studied cultivars. This could be due to the presence of both Iranian and foreign genotypes in the experiment. In the main subcluster, genotypes from both origins were present and some genotypes were showing close relationships. Significant regression associations were found between 7 morphological traits and RAPD markers and some informative markers were found for the traits. Also, in clustering of genotypes good agreements were found between the subclusters and the pollination incompatibility groups reported by other workers. The results showed that RAPD is an effective maker for study of genetic diversity among sweet cherry genotypes.

Abdollah Khadivi-Khub

Papers

Physiological and genetic factors influencing fruit cracking

Multivariate analysis of Prunus subgen. Cerasus germplasm in Iran using morphological variables

Morphological characterization of Prunus scoparia using multivariate analysis

Genetic variability and structure of Quercus brantii assessed by ISSR, IRAP and SCoT markers.

Evaluation of Genetic Diversity in Some Iranian and Foreign Sweet Cherry Cultivars by Using RAPD Molecular Markers and Morphological Traits