چكيده فارسي :
Plant genetic resources are the great gift of God to humanity. It is through them that the ground water is extracted and inserted into the water cycle in the form of vapour, and, after condensation in the clouds, returned to the earth as rain. Recent FAO data, reports that water consumption in agriculture accounts for about 67% of the total volume consumed in all sectors. 56% of the water used in agriculture is intended for livestock activities, pasture and grains, 12% for cotton, 11% for rise, 8% for sugar, 4% for grape and 4% for vegetable. Fruit sector account with about 5%, but consume is increasing because of the new high density cultivation techniques. For example, the average of water consumed per hectare for strawberry plantations is over 2000 cubic meters, and rises to over 4000 cubic meters for high density pome and stone fruit orchards. Of courses, volume of irrigation it is, in relation to local rainfall. Where rainfall is scarce, fruit growing is expensive, but not prohibitively if are adopting specific strategies to cushion the adverse effects of water shortage. Through the plants, path of water (and nutrients) takes place in three stages: Root absorption, Transport within the plant and Pass to the external environment mainly by transpiration through the stomata. A small portion of water is lost through the cuticle. Movement of water is extremely linked to species and variety, but an important role plays the rootstock. The grafted trees are formed by rootstock and scion, and sometime of a third part (the Interstock). This manipulated tree has different behaviour with respect water efficiency. For example, apple grafted onto dwarfing
rootstocks tends to have smaller xylem vessels with respect those grafted on vigorous rootstocks and this affects water transport and tree behaviour. A fruit tree grafted on rootstock characterized of fast growing and wide deep root system, has more chance of reintegrating the loses of water through transpiration. For example, combinations of peach / Missour has a root volume twice and even more of MRS2 / 5 rootstock. Water consumption and its efficiency also is affected by leaf areas and stomata, which density varies by species and variety too. Knowing how certain
chemicals affects stomata’s work, it is possible to improve the plant behaviour growing in conditions of water shortage. For example, applying of Abscisic acid (ABA) contrasts water deficit: ABA inhibit root elongation and lateral root growth, inhibit shoot growth, and shift the distribution of dry weight from shoot to root. One more example is BABA (DL-β-aminobutyric acid) that, applied daily or alternate watering for 4 months -prior to withholding water- to Royal Gala trees under drought stress conditions, has induced less transpiration, lower water stomata conductance and, even promote better photosynthesis. In using water it is necessary to take into account the phenology of the plant. For several fruits the most stress sensitive periods is spring (when the fruit expands) and postharvest (when occurs bud morphogenesis): this explains why early ripening fruits face better lack of water. It remains essential to know the water / ground relationship and take it into account right from the soil preparation prior to plant. In areas prone to water shortages, deep plough increases water storage and helps better exploring of roots. Going ahead within the plant growing season, in dry land areas is recommended summer soil tillage, as a technique capable of breaking the rise of groundwater and its lose by capillarity. Summer tillage works un-directly, as a real watering! A good alternative to tillage can be the mulching with self-reseeding cover crops (Trifolium subterraneum, Medicago polymorpha and others). The biological cycle of these species is compatible with the seasonal trend of water availability, in fact, these cover crops are sowed in autumn and grow from late winter to early summer, while when starts the dry season they disappear . The dormant seeds of these cover crops germinate in next autumn. In water / soil relationships it is very important to know the
efficiency of methods of irrigation used: poor efficiency has floating, more efficiency has the sprinklers, while the high efficiency is performed by drip irrigation. However, even by adopting high-efficiency a method is better to take into account soil structure to determine the best spatial distribution of drippers. As mentioned before, water efficiency depends primarily by the species. Some fruits species are better suited to living in drought conditions. For example Pitaya (Cerus peruvianos), Jujube (Ziziphus jujube), Cactus pear (Opuntia ficus-indica), Dragon fruit (Hylocereus spp.), Pomegranate (Punica granatum), Loquat (Eriobotrya japonica), Macadamia (Macadamia integrifolia and M. tetraphilla), Persimmon (Diospyrus kaki), Fejioa (Acca sellowiana), Almond (Prunus dulcis), Pistachio (Pistacia vera), Grape (Vitis vinifera), Olive (Olea europea), Pecan (Pecan illinoensis) Azarole (Crataegus azarolus) Sorb (Sorbus domestica), Strawberry tree (Arbutus unedo), Fig (Ficus carica), Mulberry (Morus alba and M. nigra), Strawberry guava (Psidium cattleianum), Russian olives (Eleagnus spp.), Carob tree (Ceratonia siliqua). The above
list may to include Stones and by Pomes fruits, but by following some prescriptions: uses of early varieties and of selected rootstocks. For examples:
• Almond grafted onto bitter almond seedlings to which it has total affinity, is very suitable for calcareous and dry soils; or on GF 677 hybrid of P. persica × P. amygdalus that has good grafting compatibility, induce high vigour and high yield, and also performs well on calcareous soils, little bit salted.
• Apricot grafted onto GF 677 (with peach Interstock) has good grafting compatibility, adaptability to drought, has high vigour, and induces early entry bearing.
• Cherry grafted on Colt (P. pseudocerasus) or Maxma 14 (P. mahaleb), Piku 4 (hybrid) or SL64 (P. mahaleb) all of them rootstocks suitable for hilly areas and in dry lands.
• Peach grafted onto GF 677 to be preferred for its high vigour, induces high production and has wide adaptability to all types of soil (also
poor, drought and with active files ≤ 13%); or on ROOTPAC 90 Greenpac (peach x almond hybrids characterized by different vigour), which has good grafting compatibility to all cultivars, and induces high yield, early bearing.
• Plum grafted onto Myrobalan seedlings or clonal Myrabolan 29C, induces good vigour, high grafting compatibility, good adaptability in arid soils and marginal lands, delays flowering and sprouting.
• Apple grafted onto wild apple seedlings in dry land conditions performs better than clonal rootstock, although induces trees variability in the orchard.
• Pear grafted onto wild pear seedlings but induces a significant delay in the production, or onto Fox 9 very rustic clonal rootstocks of P. communis, with large root apparatus and good anchorage.
In conclusion, knowledge on plant physiology, selection of proper crop-species and rootstock and knowledge and management of soil, can help to grow trees under water shortage condition. In some dry lands of North
Africa, peoples knows that to grow olive must planting trees grafted onto Olea oleaster wild rootstock and not the own rooted tree, more sensitive to drought. Unfortunately, arid lands and water scarcity are everywhere and the Humanity must be aware that this problem in future is going to become worsening. Intensive cultivation and high production is equal to intensive exploits of natural resources. Probably it should develop a new approach of fruit culture where sustainability should have priority of high yield. It s time to learn from past wrongs and be in Peace to the Nature.
