Abstract
For adequate yields in apple plantations, during the long growing period of the fruit primordia, one of the decisive factors is water supply. 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 tolerance of different varieties. The plantation of apple varieties grafted on various stocks and cultivated according to different systems (irrigated, non irrigated, integrate and biological) has been examined continuously by leaf analysis. Along the period of growing fruits, measurements were made in the field, then the leaf samples were analysed in the laboratory for composition of pigments, carbohydrates and antioxidants, as well as the histology of the tissues checked. Without irrigation, the mean leaf mass and the relative chlorophyll content (SPAD) of the variety Idared on M4 stocks increases beyond the values of 50 SPAD, whereas on M26 stock and integrated system, it declines. In the collection of varieties, 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 of carbohydrate 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 of SPAD 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 and is related with the density of stomata, cannot used for the selection of water-exigent varieties but for (drought) tolerant ones. In integrated culture, the (drought) susceptible varieties display (water-soluble) hydrophilic and lipophilic antioxidants (ACWand ACL resp.) the quantity of which may have some role in drought tolerance.
Highlights
In the intensive apple plantations, which are multiplied nowadays on a worldwide scale, water supply became a limiting factor
Our results prove that the supply of nutrients and of water produced tight correlation between SPAD and leaf weight (r=0.9197) but only in the moderately drought susceptible group of varieties, where within the interval 44–52 of SPAD values caused the reduction of leaf weight
SPAD measurements in the field may trace the accumulation of organic matters, which is documented with the increasing leaf weights being correlated (r=0.76-r=0.88), but it depends on the variety
Summary
In the intensive apple plantations, which are multiplied nowadays on a worldwide scale, water supply became a limiting factor. The dwarfing stocks are especially compromised by their shallow root system. The restriction of uptake of nutrients impairs the fruit size and yield. The critical period of fruit development is most susceptible. Lack of water is responsible for the declining yields (Green et al 2003, Caspari et al 2004). Poor water supply diminishes the uptake of nutrients, the leaves grow smaller, less pigmented, take a spoon form, delicate shoots, fruits develop poor colour (Zatykó, 2003)
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