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Esther Giraldo, Margarita López-Corrales, and José Ignacio Hormaza

Most descriptor lists for the characterization of genetic resources in plants include a large number of traits whose evaluation is a lengthy and expensive process making the characterization of large germplasm collections difficult. Consequently, to facilitate the study and the conservation of germplasm, it is important to select carefully the most informative variables for each species. In this work, we applied sequential statistical procedures to select the most discriminant variables in fig (Ficus carica L.) from the initial 134 qualitative variables studied. A total of 34 variables was finally selected and broken down in 97 characters that were grouped by principal component analysis in 11 principal components that explain 93.34% of the total variability. The unweighted pair group method with arithmetic mean dendrogram derived from a similarity matrix generated using the Pearson's correlation coefficient among the 11 principal components selected classifies the cultivars in four main groups mainly based in the production type. These results show that redundant information can be obtained in morphological studies with a large number of variables resulting from correlation between variables. Consequently, a carefully selected and reduced number of highly discriminating variables can allow efficient fig germplasm characterization and discrimination resulting in significant savings of time and resources.

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María Engracia Guerra, Ana Wünsch, Margarita López-Corrales, and Javier Rodrigo

Flower emasculation is widely used in breeding programs for hybridization of fruit trees. In japanese plum (Prunus salicina), some genetic crosses made by emasculation have resulted in very low or lack of fruit set, but the causes leading to this situation are not clear. In this work, the influence of flower emasculation on fruit set was evaluated in four japanese plum-type cultivars by comparing cross-pollinations performed with and without emasculation. Fruit set and fruit drop in the crosses were characterized until harvest. To ascertain which factors in the reproductive process could be related to the lack of fruit set, compatibility was determined for each cross by the observation of pollen tube growth under the microscope and by polymerase chain reaction. Likewise, the stage of ovule development was observed under the microscope in emasculated and non-emasculated flowers. An analysis of the different pollination treatments and the study of the compatibility relationships helped to dismiss factors that intervene in the reproductive process and to identify flower emasculation as the cause of premature degeneration of ovules and its implication in determining subsequent fruit set.

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Esther Giraldo, Margarita Lopez-Corrales, and Jose Ignacio Hormaza

Common fig (Ficus carica L.) is an underused fruit crop cultivated in Mediterranean countries since antiquity. In this study, 20 simple sequence repeat (SSR) loci were used to characterize 209 fig accessions conserved in an ex-situ field germplasm collection. A total of 78 fragments were amplified with the 20 pairs of SSR primers, with an average of 3.9 alleles per locus and a size between 120 and 376 bp. The mean expected and observed heterozygosities were 0.36 and 0.41, respectively. The total value for the probability of identity was 6.8 × 10−4. The SSRs studied resulted in identification of 98 unique genotypes (46.86% of all accessions preserved in the bank), indicating a high number of synonyms. Unweighted pair group method with arithmetic averages (UPGMA) cluster analysis did not show clear groups based on geographic distance, although some specific groups related to fruit type were observed. The results confirm the usefulness of microsatellites for the identification of genetic diversity and potential value of germplasm management for fig.

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María Engracia Guerra, Ana Wünsch, Margarita López-Corrales, and Javier Rodrigo

Some japanese plum (Prunus salicina) cultivars are particularly prone to erratic fruit set showing very low or even null fruit set for reasons that are not clear. To ascertain the causes of lack of fruit set in some of them, different factors intervening in the reproductive process have been evaluated using flowers of three cultivars, Angeleno, Rubirosa, and Sweet August, from commercial orchards with records of very low fruit set in previous seasons and compared with a producing cultivar, Simka. Different cultivars coincident at flowering with the cultivars studied were evaluated as adequate pollenizers in each orchard. To determine which factors that intervene in the reproductive process could be related to the lack of fruit set, microscopic observations of pollen germination, pollen tube growth, pollen–pistil incompatibility, and ovule development were analyzed in flowers of different pollination treatments. Results allowed dismissal of pollen viability, pollen transfer, and pollen–pistil incompatibility as the cause of lack fruit set. However, the observation of ovule development revealed a high incidence of premature ovule degeneration on final fruit set in the three low-producing cultivars. The lack of fruit set in orchards with no apparent adverse environmental conditions is traditionally studied by analyzing the pollination process and the pollen–pistil incompatibility relationships, but the stage of development of the ovules is not usually considered. The approach used in this work may prove valuable to other species and situations of lack of fruit set, which could help to identify the causes for premature ovule degeneration.