Mohawesh O., Al-Absi K. (2009).

Abstract

The effect of five irrigation regimes in the main fruit growth phase: rates of 0.20, 0.40, 0.60, 0.80, and 1.00 of “Class A” pan evaporation rate on the performance of two apples genotypes, namely 'Red Ace Golden Delicious' and 'Red Edna' grafted on MM106 rootstock were studied under field conditions. The crop was harvested on 15 Sep. 2008 and fruit size and weight were determined. Biochemical parameters: chlorophylls, proline, and physiological parameters already known as stress indicators in apple trees: net photosynthesis (A), stomatal resistance (Rs), transpiration (E) and intercellular CO2 concentration (Ci) were measured in leaves of apple trees subjected to different irrigation regimes. Fruit number and yield per tree were determined in the field. Subsequently, fruit flesh firmness, total soluble solids (TSS), and titratable acidity were measured. Transpiration rate (E) did not differ significantly among the treatments in all sampling dates for both cultivars. Photosynthesis reduction and the stability of intercellular CO2 concentration (Ci), as water stress developed among the whole treatments, suggested that CO2 availability in the mesophyll was not a principle cause of the decrease in A. The instantaneous water use efficiency of the plant contrast with E. Chlorophyll concentrations varied among the treatments and the cultivars. However, the differences were not statistically significant. Leaf's proline content increased for both genotypes under drought conditions. Fruit acidity and TSS relatively decreased with increasing irrigation water for both genotypes.

Advances in Hort. Sci. 23(3), 158-165.