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- Author or Editor: Rafel Socias i Company x
Flower bud density, spur density, and number of flower buds per spur were evaluated in 57 almond cultivars and selections during 3 consecutive years to establish their repeatability as well as their potential to ensure a sustainable commercial production. These three traits showed a high variability with significant differences between genotypes and years as well as a significant interaction of genotype and year. The effect of location and the interaction of location and genotype were not significant for bud density, but they were for spur density and number of flower buds per spur. Variability of flower bud density is mostly related to the number of flower buds per spur as indicated by the higher repeatability of spur density than that of the other two traits. A high flower bud density is essential for a sustainable production, because a high number of flowers may compensate frost damage. Early selection for a high flower bud density can be done indirectly through selection for a high spur density but requires its evaluation over several years.
Nut and kernel dimensions and sphericity, shelling percentage, oil content, and fatty acid composition were studied over 2 years in 15 advanced almond (Prunus amygdalus Batsch) selections. The aim was to test the effect of pollination type on these fruit traits for this group of new self-compatible selections of a mostly self-incompatible species as well as the yearly effect on these variables. Variability between selections was much higher than that between years, showing a moderate level of year-stability and a significant year effect only for some variables. The different pollination treatments affected all chemical components studied, as well as nut and kernel weight, but not the other physical traits. Self-pollination decreased kernel weight and volume as well as oil content and percentage of linoleic acid but increased the percentage of oleic acid. These variations in the fatty acid composition were in the trend of increasing kernel quality. Inbreeding depression could also negatively affect several aspects of nut and kernel quality. Thus, autogamous almond genotypes without apparent symptoms of inbreeding depression may yield kernels of increased nutritional and industrial quality.
The pistil (S-RNase) and the pollen [S-haplotype-specific F-box protein (SFB)] components of the Sf allele, presumably conferring self-compatibility in almond {Prunus amygdalus Batsch [syn. P. dulcis (Mill.) D.A. Webb]}, were identified and sequenced in ‘Ponç’, a local Spanish almond cultivar, confirming their identity with the published sequences of these components. Despite the presence of the Sf allele, the ‘Ponç’ phenotype was self-incompatible as confirmed by different pollination tests, including self pollen tube growth, fruit set after self-pollination, and fruit set in bagged branches. However, the pistil and the pollen of ‘Ponç’ were fully viable when pollinated by a cross-compatible pollen or used on a cross-compatible pistil. The fact that ‘Ponç’ presents two different S-proteins with RNase activity may indicate an active function of its Sf -RNase, whereas in the self-compatible almond cultivars thus far studied, the Sf -RNase has been inactive. This activation indicates that the presence of the Sf allele may not be the exclusive source of self-compatibility in almond, and other factors may also be involved in the expression of almond self-compatibility.
Phytosterols are important dietary components that contribute to reducing serum cholesterol levels. The objective of this research was to assess genetic diversity for total content and profile of free and esterified phytosterols in a world germplasm collection of almond [Prunus amygdalus Batsch; syn. P. dulcis (Mill.) D.A. Webb]. Steryl glycosides and acylated steryl glycosides were not measured. Fruit from 160 almond accessions were collected in 2009 and 2010. Kernel phytosterol content ranged from 1126 to 2769 mg·kg−1 in 2009 and from 1191 to 2777 mg·kg−1 in 2010. The phytosterol fraction was mainly made up of β-sitosterol (from 59.1% to 84.1% in 2009 and from 55.9% to 84.6% in 2010) and Δ5-avenasterol (from 8.9% to 25.4% in 2009 and from 8.5% to 28.2% in 2010). Significant genotypic effects were observed for kernel phytosterol content and concentration of major phytosterols. Kernel oil content was positively correlated with kernel phytosterol content in both years. The results suggested that almond germplasm contains genetic variability for both phytosterol content and profile that can be used for developing cultivars with increased levels of phytosterols and contrasting phytosterol profiles. Positive correlation between kernel phytosterol content and kernel oil content suggests the feasibility of simultaneous selection for both traits.
Several approaches have been used in evaluating self-compatibility in almond. These include fruit set after self-pollination and bagging, pollen tube growth, and the more recent Sf allele identification by molecular markers and gene sequencing. However, none of these methods have given fully reliable results because they all show advantages and limitations. Pollen contamination may distort pollination results as well as inaccuracies during fruit setting operations. Factors other than self-compatibility such as inbreeding may affect fruit set and pollen tube growth. Detection of S alleles by RNase activity and polymerase chain reaction analysis by consensus primers has not always been conclusive. The differential phenotypic expression of the Sfa and the Sfi alleles has revealed that the presence of the Sf allele is not the only requirement for self-compatibility expression in almond. As a consequence, the coding region of the Sf allele may not be the sole factor involved in that expression, which may be caused by modifier genes outside this region. Missequencing of alleles has also created confusion for allele identification. Thus, self-compatibility evaluation in almond must involve a better knowledge of the plant material as a whole, and not only of its genotype. All factors involved in setting a commercial crop in conditions of solid plantings of a single cultivar must be put together to evaluate almond self-compatibility. This approach is fundamental for the understanding of self-compatibility in almond and for the evaluation of the new selections in a breeding program.
‘Mardía’ is a new almond cultivar released because of its good agronomical traits and very late blooming time, 2 weeks later than ‘Felisia’, the latest blooming cultivar released so far. It is characterized by its slightly upright growth habit, early ripening, high and regular bloom density, autogamy (S6Sf genotype), high fruit set, tolerance to diseases, hard shell, large kernel, very high content of oleic acid, and low content of linoleic acid.
The oil content and the percentage of the main fatty acids were determined in a set of 73 almond (Prunus amygdalus Batsch) cultivars from 10 different countries present at the almond germplasm collection of the Centro de Investigación y Tecnología Agroalimentaria de Aragón, Spain (CITA). Wide variability was observed for oil content, ranging from 51.5% to 66.8% on a dry weight (DW) basis. For the main fatty acids in the lipid fraction, the variability ranged from 62.9% to 77.3% for oleic acid, from 14.0% to 26.8% for linoleic acid, from 4.9% to 7.0% for palmitic acid, from 1.5% to 3.4% for stearic acid, and from 0.3% to 0.6% for palmitoleic acid. No correlations were found between the oil content and the percentages of the different fatty acids, but a significant negative correlation was found between the percentages of oleic and linoleic acids. Principal component (PC) analysis showed that palmitic, oleic, and linoleic acids and the oleic acid/linoleic acid ratio were primarily responsible for the separation on principal component 1. The content of each component was not related to the country of origin of the different cultivars, indicating that almond fatty acid composition is genotype-dependent. Cultivars with high and stable oil content and low linoleic acid should be selected as parents in a breeding program to increase kernel oil stability and nutritional value.
Genetic diversity of the Spanish national almond (Prunus amygdalus Batsch) collection was characterized with 19 simple sequence repeat (SSR) markers selected because of their polymorphism in almond and other Prunus L. species. A total of 93 almond genotypes, including 63 Spanish cultivars from different growing regions, as well as some international cultivars and breeding releases were analyzed. All primers produced a successful amplification, giving a total of 323 fragments in the genotypes studied, with an average of 17 alleles per SSR, ranging from 4 (EPDCU5100) to 33 (BPPCT038). Allele size ranged from 88 bp at locus PMS40 to 260 bp at locus CPPCT022. The heterozygosity observed (0.72) was much higher not only than in other Prunus species, but also than in other almond pools already studied. The dendrogram generated using the variability observed classified most of the genotypes according to their geographical origin, confirming the particular evolution of different almond ecotypes. The SSR markers have consequently shown their usefulness for cultivar identification in almond, for establishing the genetic closeness among its cultivars, and for establishing genealogical relationships.
Most of the self-compatible (SC) cultivars of almond [Prunus dulcis (Mill.) D.A. Webb. syn. P. amygdalus Batsch] have the Sf haplotype. In this study, we cloned and characterized the S locus region of the Sf haplotype of SC ‘Lauranne’. The relative transcriptional orientation of SFBf and Sf-RNase and the physical distance between them are similar to those of other functional self-incompatible (SI) S haplotypes of Prunus, indicating that the genomic structure of the SC Sf haplotype appears to be intact. Although there is no apparent mutation in the coding sequence of SFBf , the Sf-RNase sequence in this study and previously reported Sf-RNase sequences show discrepancies. First, as opposed to previous indications, the ‘Lauranne’ Sf-RNase sequence encodes a histidine residue in place of a previously reported arginine residue in the conserved C2 region of Prunus S-RNase. Direct sequencing of the polymerase chain reaction products from the Sf-RNase of ‘Tuono’ confirmed that ‘Tuono’ Sf-RNase also encodes the histidine residue. We found another difference in the ‘Lauranne’ Sf-RNase sequence and other reported Sf-RNase sequences. Namely, ‘Lauranne’ Sf-RNase encodes a phenylalanine residue in place of a previously reported leucine residue in the conserved C5 region of Prunus S-RNase. This is also the case for ‘Tuono’ Sf-RNase. Expression analysis of Sf-RNase and SFBf by reverse transcriptase–polymerase chain reaction showed that Sf-RNase transcripts were barely detectable in pistil, whereas SFBf transcripts were accumulated at a similar level to the level that was observed with SFB of other functional SI S haplotypes of almond. We discuss the possible molecular mechanisms of SC observed with the Sf haplotype with special references to the expression of Sf-RNase.