Introduction of Marula, an unexploited fruit tree from Southern Africa, to the Israeli Negev

Marula (Sclerocarya birrea subsp. caffra) is a medium-sized tree native to southern Africa producing edible plum-sized drupes utilized by rural people. Marula was examined by us with the aim of introducing new orchard crops to the Israeli Negev Desert. Young seedlings grown from seeds obtained from Botswana were planted in 1985-86 in four different locations in the Negev: Besor - moderate temperatures and good quality water (electrical conductivity, EC = 1 dS m^-1): Ramat Negev Experimental Station - low winter temperatures (lowest, -7°C) and two water qualities, good and brackish (EC = 3.5-4 dS m^-1); Qetura and Neot Hakikar - both warm sites, with summer temperatures that may rise to 46°C, and brackish water with similar EC (3.5-4 dS m^-1), but with a higher concentration of Na⁺ and Cl^- at Neot Hakikar. Growth was faster and yields were higher at Qetura and lagged behind at the other sites, especially at Ramat Negev, where frost events severely damaged the young trees. Results from a new plot established nearby at Kibbutz Revivim indicate that under certain growth conditions marula can also succeed in the Ramat Negev region. The trees differed in their flowering time, which ranged over 3-4 months (spring-early summer). Marula fruits abscise at the green stage, abscission time being related to the flowering time. Fruits collected immediately after abscission ripened after 14-17 days of storage at 20°C. During ripening the fruits turned yellow, firmness and acidity significantly decreased, and soluble sugars and soluble solids concentrations increased slightly. A surge of ethylene occurred toward the end of the ripening stage. Individual trees varied in fruit weight and the proportion of various fruit components. The main limitations to fresh consumption were the low content of flesh, presence of fibers in the flesh, and the thick peel. It was concluded that marula may be used as an industrial fruit crop in the arid regions of Israel where high summer temperatures and the brackish irrigation water restrict the cultivation of most common fruit trees.