Study of Responses of Different Seedlings of Apple (Malus domestica Borkh.) to Water Stress.

The objective of this work was to study the morphological and physiological responses of apple seedlings of different cultivars to short-term water stress by irrigation with water and different osmotic potential of PEG 6000. Experiments were performed in a green house on three month old seedlings of different apple cultivars (Malus domestica Borkh. Cv. Rubinette, Golden Delicious, Elstar and Cox Orange). Water stress was induced by water reduction and by polyethylene glycol (PEG)6000. Part of plants were irrigated three times a week, as control. Others were irrigated one time per ten days and one time per 20 days. Water stress with PEG solution was induced by two osmotic potentials of -0.7 and -1.6 MPa, plant length, number of leaves, leaf area, water content, fluorescence, chlorophyll value and proline accumulation were measured. The results suggest that water stress by water irrigation (20 days drought) or by PEG 6000 showed different effects on the morphological and physiological characteristics of apple seedlings. Water stress induced by PEG decreased plant leaves number, leaf area and plant length significantly in Golden Delicious and Elstar, but there was no significant difference in Rubinette and Cox Orange compared to the control. Water content in leaves of Rubinette and Golden Delicious were decreased by high water stress after 20 days drought and by PEG treatments, however Elstar and Cox Orange were less affected. Fluorescence and chlorophyll value were not significantly affected by short term water stress. The results indicated that Proline accumulation depends on apple cultivar. This work showed a gradientof drought stress effects in the order of different varieties Golden Delicious, Elstar, Rubinette and Cox Orange. Cox Orange was highly affected by water stress. Rubinette, a cross between Golden Delicious and Cox Orange, showed a moderate tolerance. Elstar which is a progeny of the cross between Golden Delicious and Ingrid Marie, can be classified as tolerant, while Golden Delicious was the most tolerant variety in the test of seedlings.