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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.

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Octavio Arquero, Diego Barranco and Manuel Benlloch

The effects of potassium (K) status and water availability in the growth medium on growth, water content, water-use efficiency and stomatal conductance was studied in mist-rooted `Chemlali de Sfax' olive (Olea europaea L.) cuttings grown in a perlite substrate. Potassium starvation produced dehydration of all parts of the plant, reduced shoot growth and water-use efficiency. By contrast, K starvation enhanced stomatal conductance in well-irrigated plants and, even more, in water-stressed plants. These results suggest that moderate K deficiency in olives may impair the plant's ability to regulate stomatal closure; this may account for the dehydration observed in K-starved plants, particularly in situations of water stress. This result is of great importance for agricultural practices of this crop, because K status, which may not be considered deficient, can cause disorders in olive trees.

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Diego Barranco, Isabel Trujillo and Pilar Rallo

The cultivar Oblonga may have originated from a volunteer seedling at an orchard near Corning, Calif., about 1940. Its main virtue is its high degree of resistance to Verticillium dahliae. `Frantoio' is the main variety in Italy and has been planted worldwide because of its high content of top-quality oil. In the present study, we show that both cultivars have the same fifteen morphological and eight agronomical traits and both have amplified the same patterns for 22 RAPD primers and five SSRs. This indicates that `Oblonga' and `Frantoio' are probably the same cultivar.

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Luis Rallo, Diego Barranco, Raúl de la Rosa and Lorenzo León

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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.

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Diego Barranco, Octavio Arquero, Carlos Navarro and Hava F. Rapoport

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Diego Barranco, Natividad Ruiz and María Gómez-del Campo

This study aims to determine the relationship between laboratory frost-resistance data for the leaves of eight olive cultivars and observed field resistance in the same genotypes undergoing natural frost damage. The lethal freezing temperature (LT50) for each cultivar was established by measuring the electrical conductivity (EC) of the medium into which solutes from damaged leaf tissue were leaked. The value obtained was then correlated with percentage frost shoot for the same eight cultivars damaged by natural frosts in a field test. A negative correlation was observed between the percentage frost shoot and leaf LT50 for all the cultivars under study. The most frost-hardy cultivars (`Cornicabra', `Arbequina', and `Picual') were those presenting the lowest percentage frost shoot and lowest LT50. Conversely, the most frost-susceptible cultivar (`Empeltre') displayed 100% frost shoot, together with one of the highest LT50 values (–9.5 °C). According to these results, lethal freezing temperature (LT50) calculated from leaf ion leakage at a range of freezing temperatures, seem to be a valid parameter for evaluating frost tolerance in olive cultivars.

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Aurora Díaz, Antonio Martín, Pilar Rallo, Diego Barranco and Raúl De la Rosa

We studied the self-incompatibility of two main Spanish olive (Olea europaea L.) cultivars, `Picual' and `Arbequina', by testing the selfing of the seeds with microsatellites. For this purpose, we used a rapid single-seed DNA extraction method and four highly polymorphic microsatellites. We analyzed seeds produced in branches bagged for selfing from mono- and multi-cultivar orchards in 2002 and 2003. We did not find any seed coming from selfing in the bagged branches, for either cultivar, in the two types of orchards. Additionally, we tested seeds coming from free pollination in mono-cultivar orchards from different locations. In the case of `Picual' olive, only three seeds out of the 70 collected were the product of selfing, although they came from mono-cultivar orchards located in areas where the cultivar used as the female parent was predominant. From the 20 seeds of `Arbequina' olive harvested in the middle of two high-density plantations, not one was a product of selfing. According to this, olive would behave as an allogamous species in mono-cultivar growing conditions and the pollen coming from long distances would be able to produce a normal bearing. Therefore, there is strong evidence to support the idea that the cultivars studied could be self-incompatible. Future experiments in self-compatibility should include a paternity check of the possible self seeds obtained.