Ecological drought resistance and adaptability of apple varieties

For adequate yields in apple plantations, during the long growing period of the fruit primordia, one of the decisive factors is watersupply. Indicators of stress are valuable signs for the diagnosis of drought and necessity of watering, i.e. planning the irrigation of plantations.The aim of the present study was to find reliable signs of water stress on apple trees and at the same time conclude on the drought toleranceof different varieties. The plantation of apple varieties grafted on various stocks and cultivated according to different systems (irrigated, nonirrigated, integrate and biological) has been examined continuously by leaf analysis. Along the period of growing fruits, measurements weremade in the field, then the leaf samples were analysed in the laboratory for composition of pigments, carbohydrates and antioxidants, as wellas the histology of the tissues checked. Without irrigation, the mean leaf mass and the relative chlorophyll content (SPAD) of the varietyIdared on M4 stocks increases beyond the values of 50 SPAD, whereas on M26 stock and integrated system, it declines. In the collection ofvarieties, grown according to the „integrated” system, during the development of fruits, ‘Gála’ and ‘Remo’ varieties have been affiliated to the“less susceptible” group regarding drought tolerance because of the leaf morphology, structure and content of SPAD and antioxidants.However, ‘Idared’ and ‘Jonagold’ belong to the “susceptible” group. To the same group are ranged the ‘Akane, Red Rome vanWell, Pink Lady’varieties. Those varieties reacted to a short period of drought by increased production (content) of carbohydrates. Regarding changes ofcarbohydrate content ‘Greensleeves’ and ‘Ozark Gold’ varieties belong to the moderately water dependent (requiring) group. In the field,SPAD-tests facilitated the measurement of nutrient-uptake and incorporation, which is proved by the tight correlation between the data ofSPAD and the increment of leaf weight (r=0.76–r=0.88), however, this depends on the variety too. SPAD is an indicator of water supply andis related with the density of stomata, cannot used for the selection of water-exigent varieties but for (drought) tolerant ones. In integratedculture, the (drought) susceptible varieties display (water-soluble) hydrophilic and lipophilic antioxidants (ACWand ACL resp.) the quantityof which may have some role in drought tolerance