Crop yield response to water - Cra

Lead AuthorJordi Marsal(IRTA, Lleida, Spain)Contributing AuthorsJoan Girona(IRTA, Lleida, Spain),Amos Naor(GRI, University of Haifa, andMigal - Galilee TechnologyCenter, Israel)PearIntroduction and BackgroundPears, along with peaches, are the second deciduous fruit tree speciesin economical importance after apples. The genus Pyrus includes about20 wild species and its primary centre of origin is Europe, and regionsin temperate Asia. Two main species are cultivated. European pear (Pyruscommunis L.) is grown in Europe, United States, South Africa and Oceania,and the Asian pear or Nashi (Pyrus pyrifolia Burm.) (syn. Pyrus serotina) istraditionally grown in Asia. Other species of the genus have been used asrootstocks such as Pyrus calleryana Dcne. Today the most widespread rootstockis clonal quince (Cydonia oblonga L.), though its graft compatibility is not goodfor all cultivars.The cultivated pear is self-incompatible, and cross-pollination with othercultivars is required for optimum fruit production, with the exception ofsome varieties such as Bartlett and to some extent Conference. Pears typicallybear fruit on spurs in terminal buds. Flower buds are initiated at the end ofshoot development during the preceding season, and the formation of theseflowers depends on the light received by spurs in the previous season. An opencanopy is thus required for full fruitfulness by training branches and pruningto specific shapes.Other factors that influence flower bud initiation are previous crop load andwater stress. Water stress, to a certain extent, can be a positive stimulus for budinitiation, but a high crop load has a negative influence in the next season. Forthis reason pears often exhibit biennial alternate bearing. Another key issuein pear orchards is growth control to prevent decreased light penetration intothe canopy. Water stress, vigour controlling rootstocks, and growth regulatorsare means available to reduce vigour in pear orchards. Pears are grown in awide-range of climates, from cool to warm and from humid to arid-areas. In2009, there were 1.58 million ha of pear orchards globally with an averageyield of 14.2 tonne/ha (FAO, 2011). Figure 1 presents the production trends ofthe major producing countries. The major factors limiting for the expansionof pear production in warm regions are insufficient chilling temperaturesduring winter and the occurrence of diseases such as fireblight. Pear trees arenot a drought resistant species and its commercial production in areas withdry seasons depends entirely on irrigation. As far as irrigation is concerned,pear orchards may benefit from judicial use of deficit irrigation because it canhave positive effects by controlling tree vigour during current season and onflowering in the following season.376crop yield response to water