Endogenous changes exhibited by Le-Conte pear trees subjected to various irrigation regimes and their impact on vegetative growth

      This study was carried out during three successive seasons 2013, 2014 and 2015 on seventeen years old Le-Conte pear trees. The first season was a preliminary season to eliminate the residual effects of the previously used irrigation treatments. Pear growing season was into four  phenological stages (stage I beginning of flowering to final fruit set, stage II from initial fruit set to final fruit set, stage III final fruit set to harvesting and stage IV  harvesting to leaf shed). Control trees received 100 % of crop water requirement during all stages while the remaining trees received either of three water regimes (60, 80 or 120% of crop water requirement) applied at one of the specified phenological stages and then irrigated with 100% of the requirements for the remaining. The effects of applied regimes on some vegetative growth parameters, enzymatic activities activity, phytohormons, total proteins, carbohydrates, phenols and proline were assessed. Results showed clear enhancements in vegetative growth induced by applying 120% of the actual requirement during any of the considered stages, proline declined by increasing the applied water quantities, whereas, an opposite trend was evident with protein content. Lowest irrigation regime (60%) added at any of the considered stages significantly induced highest leaf carbohydrates, phenol content, polyphenol oxidase (PPO) & Peroxidase (Pro) activates, ABA and SA content when compared with higher irrigation regimes at same stages. Growth promoting hormones as GA₃, IAA and CKs contents attained an opposite trend. Finally it was concluded that various responses of vegetative growth to applied regimes was a reflection of the endogenous changes exhibited by the trees.