November 25 pm The Physiology of Adaptation and Yield Expression in Olive D.J. Connor* Instituto de Agricultura Sostenible (CSIC) and Universidad de Córdoba Apartado de Correos 4084 14080 Córdoba, Spain and The Institute of Land and Food Resources The University of Melbourne Victoria 3010, Australia E. Fereres* Instituto de Agricultura Sostenible (CSIC) and Universidad de Córdoba Apartado de Correos 4084 14080 Córdoba, Spain I. INTRODUCTION II. GROWTH AND DEVELOPMENT A. Vegetative Growth B. Floral Induction, Initiation, and Differentiation C. Response of Flowering to Temperature D. Flowering, Pollination, and Fertilization E. Self Compatibility F. Fruit Set, Filling, and Maturation G. Efficiency of Reproductive Strategy III. WATER RELATIONS A. Collection of Water by Root Systems B. Leaf Anatomy and Water Relations C. The Olive Tree as a Hydraulic System D. Control of Transpiration IV. MINERAL NUTRITION A. Deficiencies and Toxicities B Extraction and Cycling of Nutrients in Orchards V. CARBON ACCUMULATION A. Leaf Photosynthesis B. Interception of Radiation C. Tree and Canopy Photosynthesis VI. BIOMASS PARTITIONING AND REALIZATION OF YIELD A. Movement of Assimilates from Leaves B. Above- and Below-Ground Biomass C. Shoots and Fruits D. Assimilate Supply and Oil Formation VII. STRESS PHYSIOLOGY A. Drought B. Low Temperature C. Salinity D. Waterlogging 1 VIII. INTEGRATION OF RESPONSES IX. RECOMMENDATIONS FOR FUTURE RESEARCH A. Phenological Development B. Carbon Assimilation and Partitioning C. Water Relations D. Nutrient Balance X. CONCLUSION *We thank Antonio Hall, Bob Loomis, María-Inés Mínguez, Hava Rapoport, David Smith and four reviewers for comments and suggestions on the manuscript and also Joan Girona, Miguel Pastor, Francisco Villalobos, and Francisco Orgaz for valued discussion. David Connor’s study in Spain was funded by the Ministerio de Educación y Cultura, Spain. List of Abbreviations A leaf photosynthetic rate Amax maximum rate of leaf photosynthesis ATP adenosine triphosphate CAM crassulacean acid metabolism CC canopy (vertical) cover CoA coenzyme A CR constructional respiration EC electrical conductivity ET evapotranspiration ET0 reference crop evapotranspiration FAS fatty acid synthase FRF fruit retention force GR glucose requirement for growth or maintenance LAI leaf area index LSC leaf specific hydraulic conductivity MPK monopotassium phosphate MR maintenance respiration NADH nicotinamide-adenine dinucleotide phosphate NUE nitrogen-use efficiency PAR photosynthetically active radiation PRD partial root zone drying PS phenological stage Q capacitance RDI reduced deficit irrigation RLD root length density RUE radiation-use efficiency SLM specific leaf mass T transpiration rate TAG triacylglycerol TE transpiration efficiency 2 VPD vapor pressure deficit WUE water-use efficiency 3 I. INTRODUCTION Olive (Olea europaea L., Oleaceae) has probably been in cultivation longer than any other tree species. It was domesticated around 3000 to 4000 BC in the eastern Mediterranean and from there was spread widely in northern Africa, the Iberian Peninsula, and the rest of southern Europe by civilizations that successively occupied the region. Whereas olive is now renowned for high-quality food oil and for fruit for direct consumption, it was originally harvested for oil used as medicine, lamp fuel, and lubricant. During the last 500 years, olive has been taken to the Americas, South Africa, Australia, China, and Japan, but remains principally a crop of the Mediterraean Basin which accounted for 95% of world mean annual production of 2.5 Mt oil during three years to 2002. Of the five major producers, Spain, with 42% of world production, was ahead of Italy, Greece, Turkey, and Tunisia (FAOSTAT 2003). All cultivated olive belongs to a single species (O. europaea) along with the wild ancestors from which it was selected. As a result of the general use of vegetative propagation and the longevity of individual trees, many olive cultivars are probably within several generations of the wild types from which they were selected (Lavee 1990). Many trees are hundreds of years old and some may be thousands. Based on local knowledge, Miranovic (1994) reports 1000-year-old olive orchards of ‘Zutica’ on the Montenegrin Coast, with one tree over 2000 years. As a consequence, most traditional olive-growing regions depend on only a few of the more than 2000 recognized cultivars and clones. Similarly, small numbers of cultivars dominate production in each of the major, intensive areas of Spain, Greece, and Tunisia. In Spain, for example, of 262 recognized cultivars, just four, ‘Picual’, ‘Cornicabra’, ‘Hojiblanca’, and ‘Lechin de Sevilla’, occupy 68% of the olive area (Barranco and Rallo 2000). In Italy, however, there is no similar dominance of few cultivars. Rather there is much variation from locality to locality. In the Mediterranean region, with its characteristic hot, low-rainfall summers, olive was developed as the crop of marginal land that was unsuitable for more intensive cultivation by reason of soil type, topography, or lack of water for irrigation. The traditional orchards are consequently of widely spaced trees, maintained with small canopy cover, and hence water demand, to ensure survival through the driest summers. The cultivation of olive is, however, changing. Large areas of widely spaced olives are being irrigated and the trees reshaped for mechanical harvesting. At the same time, most new orchards in the Mediterranean, and almost exclusively elsewhere, are being planted at high density, irrigated and fertilized for high yield, and shaped from the outset for mechanical harvesting. These changes are occurring rapidly and, in the absence of complete knowledge specific to olive, technology is being adapted from other crops, e.g. mechanical harvesting from wine grapes and reduced deficit irrigation (RDI) from stone and pome fruits (Mitchell and Chalmers 1982; Mitchell et al. 1989). Despite its long history of cultivation, scientific understanding of olive is limited compared with that of other long-standing crops such as wheat and barley, or even new crops such as sunflower (Connor and Hall 1997). Traditional management of olive was established by trial and error without physiological understanding of responses to environment and management. A relatively recent treatise on olive (Rojo 1840), for example, commenced by acknowledging the major contribution to knowledge by 4 Columela, one of the first agriculturalists from ancient Rome. Traditional techniques of olive production that have persisted for thousands of years may be optimal for local cultivars in local areas but they cannot be confidently extended to new locations or new forms of cultivation. One key to progress is to understand the physiological basis of those responses within a sound scientific framework. The recent expansion of scientific research in olive justifies this new comprehensive review. New cultural techniques, with greater tree density, more water, improved nutrition, and mechanical harvesting, are both the cause and effect of new research that is expanding. This review will consider individual components of physiological response, leading to an integrated view of their interactions that determine growth, survival, resource-use efficiencies, and productivity under field conditions. It will supplement and update two previously published reviews (Bongi and Palliotti 1994; Lavee 1996), and the more restricted reviews of fruit set (Lavee 1986), salt tolerance (Gucci and Tattini 1997), water relations (Fernández and Moreno 1999), and flower induction and differentiation (Fabbri and Benelli 2000). It will evaluate the existing literature on olive within the established framework of plant and crop physiological science (see e.g. Taiz and Zeiger 1991; Loomis and Connor 1992) so that the consolidated knowledge can be applied to olive production, in whatever form, in all appropriate environments. A consequent important outcome will be the identification of areas where knowledge is inadequate and so the review will also contribute to setting priorities for future research. II. GROWTH AND DEVELOPMENT The size and activity of the foliage canopy determine the carbon gain and growth of olive trees. It is, however, the pattern of appearance of new organs that determines how that growth is progressively partitioned to buds, leaves and roots, and in consequence, how yield is determined annually and how trees change morphologically in the longer term. Olive is widely reported as a day-neutral plant in which the rate of development through its biennial vegetative-reproductive cycle is governed climatologically by temperature and sunlight (assimilate supply). Since the only experimental evidence for this day neutrality resides in work with a single cultivar, ‘Rubra’ (Hackett and Hartmann 1964), this response of olive does merit wider investigation. The biennial cycle (Rallo 1998), one in which individual trees bear in alternate years, arises because olive flowers on 1-year-old shoots and the induction of buds during summer is affected by the presence, at that time, of the current year’s fruit. The interaction between external environment and the internal physiological responses that operate over the extended period from induction in summer to flowering in spring is, however, poorly understood. Sanz-Cortés et al. (2002) developed a numerical scale for the vegetative and floral phenological stages (PS) that is consistent with scales used widely in other tree crops. This standardized