The olive (Olea europaea) and table olive industries worldwide are almost entirely supported by low-density rain-fed orchards planted with local cultivars empirically selected by farmers for centuries. New early and high-bearing plantation systems adapted to mechanical harvesting have been designed and developed during the past 50 years. Only certain traditional cultivars are well suited for these new olive plantations. The new orchards therefore require new cultivars. A long-term effort on the exploration, conservation, and sustainable use of olive genetic resources starting in Spain in 1970 has been followed by breeding programs developed since the early 1990s by the University of Cordoba, the University of Seville, and the Andalusia Institute for Agricultural, Food and Fisheries Research. We are trying to use crossbreeding to obtain new early bearing cultivars adapted to mechanically harvested orchards. Objectives related to shortening the juvenile period (JP) and developing early tests of selection, early bearing, high cropping, resistance to chief diseases (particularly verticillium wilt caused by Verticillium dahliae), industrial suitability, high oil content, diversity of olive oil composition for oil cultivars, and fruit size and quality for table olive are being pursued. Specific criteria for the adaptation of oil olive and table olive cultivars to mechanical harvesting, such as low-vigor trees with a compact growth habit, the force needed for fruit removal, natural fruit abscission, resistance to bruising, and extending the harvest time in cultivars showing homogeneous ripening are evaluated in the progenies. To date, more than 19,000 seedlings have been initially evaluated, 481 preselections are on intermediate field trials, and 31 advanced selections are being established in a network of field trials. A new protected cultivar Sikitita (Chiquitita in the United States), selected for very-high-density narrow hedgerows, was released in 2008. Recently, a first project on olive genomics is heralding the use of marker-assisted selection in the midterm phase of development. Cultivars adapted to the new mechanical harvest systems will be progressively released in the future.
Diego Barranco and Luis Rallo
The diversity and antiquity of the cultivars, their restricted distribution and the limited use of rootstocks characterize cultivated olive (Olea europaea L.) plant material in Spain. An exploration survey identified 262 different cultivars, which have been introduced in the Olive Germplasm Bank in Córdoba, Spain. Evaluation of this germplasm, field trials and a breeding program are in progress.
Lorenzo León, Luis M. Martín, and Luis Rallo
Thirteen characters were evaluated over four years in progenies from a diallel cross among the olive (Olea europaea L.) cultivars `Arbequina', `Frantoio', and `Picual' to determine if phenotypic correlations existed between these characters. Yield per tree, ripening date, oil yield components and fatty acid composition were recorded annually once seedlings began to flower and produce fruit. Significant correlations were found between several characters including oil yield components and fatty acids composition. Lower correlation coefficients were obtained between ripening date and oil and oleic acid content. Generally, yield was not correlated with the other characters evaluated. Principal components analysis confirmed the main correlations among characters and showed them to be independent of the parents used.
Hava F. Rapoport and Luis Rallo
Fruit set and enlargement were compared for fertilized and unfertilized olive (Olea europaea L.) ovaries, the latter obtained by flower emasculation and bagging to prevent pollination. In the control population, the timing of abscission coincided with the onset of ovary expansion following fertilization. In the emasculated population, ovary expansion was only slight, and abscission was substantially delayed. Separation of the ovaries by size using graduated screens provided a useful tool for the evaluation of ovary growth.
Carmen del Rio and Luis Rallo
Isabel Trujillo, Luis Rallo, and Pere Arús
Pollen samples of 155 olive (Olea europaea L.) cultivars from different origins were analyzed to study isoenzymatic variability in five enzyme systems: alcohol dehydrogenase (ADH), esterase (EST), glucose phosphate isomerase (GPI), leucine aminopeptidase (LAP), and malic enzyme (ME) using starch gel electrophoresis. Polymorphism was observed in all of the isozyme systems. ME, GPI, EST, and LAP were the most useful systems for identification of cultivars. Different combinations of banding patterns of these systems allowed us to identify 85% of the cultivars. The remainder were separated into groups of two or three cultivars that could be identified using morphological characteristics. No intracultivar polymorphisms were observed.
Raul De la Rosa, Luis Rallo, and Hava F. Rapoport
In the olive (Olea europaea L.), inflorescence and flower differentiation occur in the early spring following a period of winter chilling and dormancy of the potentially reproductive buds. We examined the size, structure, and starch content of these buds during winter rest in the field and during forcing under standard growth-chamber conditions. Basic bud structure and dimensions remained unchanged during the rest period, but starch content increased in the bud's central axis. When cuttings were forced in the growth chamber, the buds followed a morphogenetic pattern similar to that observed in the field, but the sequence of developmental events could be timed more precisely. The first changes observed were the onset of axis growth and the differentiation of axillary primordia within 3 days of transfer to the growth chamber. This was followed by the initiation of new nodes, and, at 15 to 18 days, by the first signs of floral differentiation in the terminal and axillary bud apical meristems. Bud growth and differentiation were accompanied by a decrease in starch content.
Lorenzo León, Raúl de la Rosa, Diego Barranco, and Luis Rallo
The initial results of a comparative field trial of the first 15 selections of the olive (Olea europaea L.) breeding program of Cordoba, Spain, are presented. These selections came from crosses among ‘Arbequina’, ‘Frantoio’, and ‘Picual’ that were also included in the trial as controls. The trial was planted in July 2001 in a randomized block design with 16 replications and was systematically evaluated for earliness of bearing, vigor, crop, and yield efficiency from 2001 to 2005. Significant differences among selections were found for all characters measured. A greater proportion of early-bearing genotypes than in previous cultivar collections were found, whereas mean accumulated yield was similar to former evaluations. Therefore, the shorter unproductive period obtained in this work seems to indicate that the selection of seedlings for a short juvenile period has provided a shorter unproductive period of the subsequent new cultivars. No correlation between vigor at the seedling stage and vigor in the corresponding adult vegetative propagated selection was found. If the data presented here are confirmed further, some early-bearing cultivars could be suggested as new olive cultivars, the first obtained by cross-breeding in Spain. Additionally, some of them also show a low vigor and could be adapted to high-density hedgerow orchards.
Luis Rallo, Diego Barranco, Raúl de la Rosa, and Lorenzo León
Milad El Riachy, Luis Rallo, Raúl de la Rosa, and Lorenzo León
The duration of the juvenile period (JP) before the seedlings reach the adult phase (AP) and begin flowering is the major impediment for fruit breeding in olive. In this work, the effect of soil solarization on the growth and duration of the JP of olive seedlings was studied. Seedlings obtained from open pollination of ‘Manzanilla de Sevilla’ and from crosses between ‘Arbequina’ × ‘Arbosana’ and ‘Picual’ × ‘Koroneiki’ were tested. Solarization treatment consisted on covering the soil around the trees for 3 years by black plastic film in a split-plot design with the three progenies as the main factor and solarization/not solarization as the secondary factor. Solarization resulted in both higher soil temperature and soil moisture in solarized plots with respect to non-solarized. Significant differences between crosses were found for plant vigor and flowering measurements throughout the experiment. Soil solarization increased trunk diameter and the number of seedlings reaching AP in ‘Manzanilla’ open progeny. A positive effect of solarization on flowering index was also observed in ‘Picual’ × ‘Koroneiki’ progenies. These results suggest that soil solarization may be recommended as a tool for shortening the duration of the JP and thus accelerating the selection process in olive breeding programs.