Olive production in the first few years after planting depends on how the canopy covers the hedgerow and develops flowers. Therefore, optimum irrigation management should look for the minimum amount of water required for maximum growth and bud initiation. The response of a young hedgerow olive orchard to different irrigation strategies was recorded for 3 years after planting in 2003. Observations included stem water potential (Ψstem), leaf conductance (gl), shoot and trunk growth, canopy development, and flowering. During the first year, olives received 74 mm of irrigation. During the second and third years, three irrigation treatments (T2, T3, and T4) were scaled back from a control (T1) that was irrigated to maintain soil close to water-holding capacity. T1 received 56 and 106 mm of irrigation in the second and third years, respectively. Treatments T2, T3, and T4 received 82%, 64%, and 46% of the water applied to T1 in the second year and 76%, 72%, and 29% in the third year of growth, respectively. Trees in T1 displayed different physiological and growth behaviors between years. Ψstem, gl, and shoot growth were 131%, 31%, and 56% lower in the third than in the second year, respectively. Irrigation treatment had no significant effect on evaluated parameters in the second year, except on Ψstem in T4 that fell below that of the other treatments in late September. In the third year, shoot growth, trunk diameter, and leaf area density in T4 decreased 52%, 13%, and 31% compared with T1, respectively. Nevertheless, external surface area and canopy volume were not significantly affected by irrigation treatment. The start of flowering, recorded in the third and fourth years, was not significantly affected by the irrigation received in previous years. Because water stress did not advance flowering, maximum growth should be the main objective in irrigation management of young olive orchards. No differences were observed between T3 and T1 in any of the vegetative, canopy development, or inflorescence parameters recorded, although Ψstem and gl were significantly lower in T3. During the second and third years, T3 can be considered the most efficient irrigation treatment with 36 and 76 mm of irrigation for each year, respectively.
Ana Centeno and María Gómez-del-Campo
Olive cuttings root well using synthetic auxin indole-3-butyric acid (IBA). However, European and North American regulations do not allow the use of synthetic products to obtain organic vegetative propagation materials. In this work, we evaluated different products that could replace IBA in the propagation of olive cv. Cornicabra leafy-stem cuttings. In 2003, six products with a known auxin effect were assessed: IBA, algae extract, brewer's yeast, a bed of sunflower seed, seaweed dry extract (Sm-6 Organico™), and an extract of macerated seeds (Terrabal Organico™). The basal end of cuttings was treated with one of these products and placed on a mist bed with basal temperature control. After 2 months, rooting percentage, number of roots per cutting, number of cuttings with callus formation, and number of cuttings with basal thickening were determined. No significant differences were found in rooting percentage or number of roots per cutting between IBA and Terrabal Organico™ and Sm-6 Organico™. These last products had significantly higher percentage of rooted cuttings without callus formation than IBA. In 2004, a new trial was conducted in which seven treatments were evaluated: IBA applied for 7 s; Terrabal Organico™ applied for 1, 4, and 8 h; and Sm-6 Organico™ applied for 1, 4, and 8 h. No significant differences in rooting percentage or number of roots per cutting were observed between IBA and Terrabal Organico™ applied for 1 h, whereas all the Sm-6 Organico™ treatments had significantly lower rooting percentages than IBA. Both rooting percentage and the percentage of rooted cuttings without callus development decreased significantly as treatment duration with Terrabal Organico™ increased. Therefore, Terrabal Organico™ could produce a toxic effect on cuttings when treatment duration is increased. Thus, Terrabal Organico™ could be a valid alternative to IBA in the propagation of organic olive plants of cv. Cornicabra when applied to the basal end of cuttings for 1 h.
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.