Fruit and Nut Trees--Appraising the Treasure of the Desert

Lack of water has traditional been the limiting factor in the use of deserts for agricultural production. Irrigation has often been used to overcome this constraint, but often with serious effects. Over irrigation often depletes ground water and causes salination of the soil, conditions which ultimately threaten agricultural production. Tremendous agricultural resources can be found in some deserts. Botswana, for instance, is two-thirds desert, and imports most its food, but its desert supports hundreds of wild plants that are not only edible, but taste good and are nutritious as well.

Professor Yosef Mizrahi of the Department of Plant Physiology, and other scientists at the Ben Gurion University of the Negev in Beersheva, Israel are assessing some desert plants for use in arid-lands agricultural production systems. Mizrahi began the project in 1984 . He and James Aronson, an economic botanist, gathered seed from deserts around the world, searching for fruit and nut trees for development as new orchard crops for desert regions.

Mizrahi's search for genetic material yielded 27 potential crops from which six were chosen for further research. These six include; yehib (Cordeauxia edulis); ber (Ziziphus mauritiana); pitahaya agria (Stenocereus gummosus); mongongo nuts (Ricinodendron rautaneii); white sapote (Casimiroa edulis); and marula (Sclerocarya birrea subsp. caffra). Of the six, the last three are described here. The plant material was collected and brought back to Israel where it was propagated in quarantine and transferred to four introduction orchards in arid southern Israel. The orchards were located at: Qetura, Neot Hakikar, Besor, and Ramat Negev. Thirty plants of each species were planted in each orchard. Each orchard differs from the others in terms of evaporation rate, annual rainfall, maximum/minimum temperature extremes, and soil and water characteristics-- including salinity. The water salinities are due to NaCl and CaSO4 salt types, fluctuating from 1 to 5 dS.m-1. Note that water of good quality for irrigation has a conductivity below 2 dSm-1, while sea water has a conductivity of about 46 dSm-1. Growth, phenological and physiological variables have been observed during the past five years since the project began. Soil, water and climatological data are also being collected throughout the experiment.


Sclerocarya birrea subsp. caffra, is a large, dioecious, deciduous tree which grows wild in northern South Africa and parts of eastern Botswana. The flesh of its fruit is very juicy and aromatic and is eaten fresh or processed, yielding quality jams, juices and alcoholic beverages. Inside the stone is a very small tasty nut. The fruit serves as an important source of vitamin C for the rural people. In the experimental plots many branches died due to winter temperatures of -7 degrees Celsius. In the Spring, however, all plants resumed their growth from the lower parts of the stem. Marula is easy to propagate either by shoot or root cuttings.

White Sapota

Casimiroa edulis, is a medium-sized evergreen tree from central America which can be found in backyard gardens. Growers of rare fruits in California and Florida have selected a number of high yielding cultivars with improved fruits. The fruits are medium to large with a thin green-yellow skin and cream-white sweet flesh. The seeds germinated easily and seedlings transplanted well at all locations. At Neot Hakikar the plants turned yellow with severe symptoms of NaCl leaf burn: they survived for a while and then died. At Qetura growth started in March/April and slowed down in the hottest months, namely July and August. At this time the leaves showed some symptoms of yellowing and tip burns, which vanished in the autumn. Despite these difficulties development at Qetura is satisfactory. At Besor the fastest growth occurred in May-August, and damage to leaves was not observed.

During February of 1989 the plants were exposed to -7 degrees Celsius, and not a single leaf was damaged. Three-year-old plants have started to flower at the Besor orchard. They are flowering now, and all of them are seedlings.


Ricinodendron rautaneii, is a large, dioecious, deciduous tree which grows in the wild on sandy soils between latitudes 15 and 21 degrees in southern Africa. The fruit of the tree has a thin edible flesh and a pleasant-tasting kernel contained in a hard-walled stone. The kernel weighting about 1.2 g is rich in fats (~40%) and protein (~38%) and plays a central role in the diet of the Kung San food gathering and hunting people of the Kalahari desert. The mongongo fruits abscise green when mature, and starts the ripening ( skin color change to brown, flesh softening and taste development) few days later.

Seeds germinated after treatment with ethephon [(2-chloroethyl) phosphoric acid]. (For specific information on treatment, see contact information below). Seedlings were transplanted successfully in all orchards. At Neot Hakikar after a brief growth spurt in June the plants turned yellow, showed the typical leaf burn symptoms of NaCl damage, and subsequently died. At Qetura the main growth period occurred during the spring; in mid-Summer growth slowed down. At the Besor location winter dormancy broke very late ( in June), and growth continued until November . This location is much cooler than Qetura (Table 1). In all locations some of the trees shoed signs of leaf-yellowing, which was diagnosed as iron deficiency and corrected b application of iron. The healthiest-looking trees are those growing at the Besor plot. All plants which were exposed to -7 degrees Celsius died even though the plants were in dormancy. At Qetura three-year-old plants showed severe growth inhibition together with leaf yellowing. The reason is not yet known, but salinity may be the cause. At the Besor site the plant developed very well without any interruption. Dormancy there lasted from December to May.

The project is in its fifth year now, but there is no way of predicting the eventual success of various species at the different locations. Mizrahi and his fellow researchers were able to get seeds to germinate after attempting a variety of techniques. Marula can be forced to germinate by opening the operculum in the very hard and thick seedcoat. Mongongo can germinate efficiently if the exocarp is removed and the seed treated with either ethylene or ethephon. Germination was difficult to achieve in some cases due to the plants' adaptation to the inhospitable environment of the desert. To maintain its population, these trees have seeds with low germination rates, thus staggering germination over a long period of time, and maximizing their chances at germination in favorable conditions. Transplanting the seedlings from the nursery presented other problems as desert trees often grow very deep roots early in their development.

Aside from investigating the germination, transplanting, and survival, of these trees Mizrahi is investigating the potential commercial value of the fruit. For this purpose, Mizrahi is studying the trees' fruit yields and quality. In order to develop an orchard tree crop from these wild trees, proper vegetative propagation techniques need to be developed as well. With more time and research these rare and wild fruit trees may provide arid-lands agriculture with a lucrative and sustainable alternative to expensive irrigated agriculture.

For more information contact:

Prof. Yosef Mizrahi
The Institute for Applied Research
Ben-Gurion University of the Negev
P.O. Box 1025
Beer-Sheva, ISRAEL