Table of Contents
Nerd, A. and Y. Mizrahi. 1993. Domestication and introduction of marula
(Sclerocarya birrea subsp. Caffra) as a new crop for the Negev
desert of Israel. p. 496-499. In: J. Janick and J.E. Simon (eds.), New crops.
Wiley, New York.
Domestication and Introduction of Marula (Sclerocarya birrea subsp.
Caffra) as a New Crop for the Negev Desert of Israel
Avinoam Nerd and Yosef Mizrahi*
- PLANT PERFORMANCE AND PHENOLOGY
- FRUIT RIPENING
- Table 1
- Table 2
- Fig. 1
- Fig. 2
- Fig. 3
- Fig. 4
Marula (Sclerocarya birrea subsp. caffra, Anacardiaceae) is a
large dioecious deciduous tree found in southern Africa, mostly south of the
Zambesi river (Palgrave 1984). The tree is highly prized by local people for
its fruits. Female trees bear plum-sized stone fruits with a thick yellow peel
and a translucent, white, highly aromatic, sweet-sour flesh which is eaten
fresh, or used to prepare juices and alcoholic beverages. The seeds inside the
stone are also eaten they have a delicate nutty taste and a high nutritive
value and high (up to 56%) oil content (Shone 1979).
Recently, an effort has been made to domesticate the tree in southern Africa
and Israel in order to establish orchards that will supply both fresh fruit and
fruit for the canning and beverage industry (Fig. 1) (Weinert et al. 1990; Nerd
et al. 1990). This paper describes plant performance in four introduction
orchards established at different locations in the Negev Desert of Israel and
postharvest physiology of the fruits.
Seeds collected from trees growing in central and northern Botswana were used
for propagation. One-year-old plants were planted in 1985-87 in introduction
orchards established at the following four sites in the Negev Desert:
Besor--moderate temperatures, fresh water (EC about 1
dS.m-1); Ramat Negev--subfreezing temperatures, fresh and
brackish (EC 3.5 dS.m-1) water; Qetura and Neot Hakikar
high summer temperatures and warm winters, brackish water (EC fluctuating
between 3.5 and 4.5 dS.m-1). Additional details on the
climate and soil and water properties of the four sites have been published
previously described (Nerd et al. 1990).
About thirty plants were planted in each orchard, in six blocks at Ramat Negev
and in three blocks at the other plots. The plants were drip fertigated every
one or two days in the summer and every three to five days in the winter. In
the fourth year, the amount of water supplied was determined according to the
evaporation rate (pan class A), and the plant cover, was 17 m3 per
tree per year at Besor and Ramat Negev and 25 m3 per tree per year
at Neot Hakikar and Qetura. At Ramat Negev, brackish water was applied to
three of the blocks after two years of establishment with fresh water and the
other three were irrigated only with fresh water. Growth and phenological data
were recorded periodically for each orchard. Fruits collected at Qetura were
used for postharvest physiology studies.
The height of four-year-old plants was much greater at Qetura and Besor than at
Neot Hakikar and Ramat Negev. Trunk circumference (30 cm above trunk base)
usually correlated with tree height, except for the plants at Ramat Negev whose
circumference was larger than the value predicted from the height (Table 1).
The small size of the plants at Ramat Negev may have been related to frost
damage. After one night in February 1989, when temperatures fell to -7°C,
all the branches died almost to the base of the trunk. However, all plants
resumed growth the following summer (dead portions of branches were cut back in
the spring), and the trees tended to develop more than one main stem (Table 1).
The recovered plants also produced sprouts from roots close to the base of the
tree. This phenomenon coincides with that manifested in another of our
studies, which showed that marula root cuttings prepared in the summer easily
developed new shoots. Although climatic conditions are similar at Qetura and
Neot Hakikar and both sites were irrigated with brackish water, growth at
Qetura was more rapid than that at Neot Hakikar. This finding can be related
to the higher Ca2+/Na+ ratio in the water at Qetura (1.2
at Qetura versus 0.8 at Neot Hakikar), which probably moderated the retarding
effect of salinity on growth. Brackish water irrigation of two year-old-trees
at Ramat Negev did not inhibit their growth. These results together with those
obtained at Neot Hakikar and Qetura indicate that marula has tolerance to
salinity of ~4 dS.m-1.
Breaking of winter dormancy (late spring, April-May), occurred earlier at the
warmer sites, Qetura and Neot Hakikar, than at the cooler sites, Besor and
Ramat Negev (Fig. 2). It is of interest that the initiation of seasonal growth
in common deciduous fruit trees such as peaches and apples in the Besor area
took place 1 to 2 months earlier than that in marula.
Leaf abscission started in December in all the orchards. Plants at the cooler
sites lost all their leaves within a few weeks, but those at the warmer sites
maintained up to 50% of the leaves until the next summer. Although the
breaking of dormancy can be retarded in deciduous trees that have not shed all
their leaves in the winter (Saure 1985), we did not find any inhibition of
breaking of bud dormancy in trees at the warm sites.
Yields were obtained only from the trees at Qetura. Eight of 20 trees planted
in 1985-86 produced fruits, five giving reasonable yields in 1990, with an
average yield of 26.8±10.4 kg and an average fruit weight of 28.3±2.5 g.
These fruits are relatively small in comparison with those obtained from some
selected trees in Botswana and South Africa, where average fruit weight may
reach 80 g (F.W. Taylor and L.C. Holtzausen pers. commun.).
Marula fruits abscise before ripening; at this stage the skin color is green
and the fruit is firm. Time of fruit abscission varied among trees at Qetura.
Of the eight yielding trees, fruits abscised mainly in August in six trees and
in late October in the other two. This can be attributed to genetic variation,
which can be exploited for expanding the harvest period by planting clones that
ripen at different times. The pattern of fruit abscission differed among
trees, but in all the examined trees, 80% of the fruits abscised within two
weeks (Fig. 3).
Production of CO2 and ethylene was studied in marula fruits collected
immediately after abscission. The fruits were enclosed in an air flow system
kept at 20°C, and samples of exiting air were analyzed for CO2 and ethylene
concentrations by gas chromatography (Mizrahi 1982).
The respiration rate (CO2 production) increased to a temporary peak on day 9,
and ethylene production rose concomitantly with the rise in respiration (Fig. 4). Skin color started to change on day 3, and a completely yellow color was
obtained by day 12. These results indicate that climacteric processes start
Our results contradict those of Redelinghuys (cited by Weinert et al. 1990),
who showed that abscised fruits had high respiration rates which dropped
markedly over 7 days at 23°C. However, the pattern of respiration we
observed for abscised fruits was the same as that demonstrated by Redelinghuys
for picked fruits.
Ripening of abscised fruits was affected by storage temperatures. After 14
days of storage, fruits kept at 4°C remained green and firm, while those
kept at 12° and 20°C developed a yellow color and could be squeezed for
juice (Table 2). Fruits stored at 20°C were riper than those kept at
12°C: they had a deeper yellow color, a higher juice content, and lower
acidity. The fruits stored at 4°C for 14 days were damaged by low
temperatures: brown spots developed on the green skin within five days when
they were transferred to 20°C and off-flavor taste developed.
Marula was established well at various sites in the Negev Desert, differing in
environmental conditions. Brackish water (EC ~4 dS.m-1)
can be used to irrigate the crop, and warm winters (mean temperature of the
coldest month is 15°C) do not limit the breaking of winter dormancy.
Cultivation at sites with subfreezing temperatures may not be feasible since
branches may be damaged by frost events (-7°C). However, it is possible
that hardening the trees before winter by withholding irrigation may increase
their tolerance to cold and thus enable cultivation at such sites.
Trees started to bear fruits in the fourth year, and reasonable yields (above
20 kg per tree) were obtained one year later. Full ripening (climacteric type)
occurs after abscission, and fruits can be stored for two weeks at 20°C and
longer at 12°C, while low temperatures (4°C) damage the fruits.
- Mizrahi, Y. 1982. Effect of salinity on tomato fruit ripening. Plant
- Nerd, A., J.A. Aronson, and Y. Mizrahi. 1990. Introduction and domestication
of rare and wild fruit and nut trees for desert areas, p. 355-363. In: J.
Janick and J.E. Simon (eds.). Advances in new crops. Timber Press, Portland,
- Palgrave, K.C. 1984. Trees of Southern Africa. C. Struik, Cape Town,
Republic of South Africa.
- Saure, M.C. 1985. Dormancy release in deciduous fruit trees. Hort. Rev.
- Shone, A.K. 1979. Notes on the marula. Bul. 58, Dept. of Forestry, Pretoria,
Republic of South Africa.
- Weinert, I., A.G., P.J. van Wyk, and L.C. Holtzhausen. 1990. Marula, p.
88-115. In: S. Nagy, P.E. Show, and W.F. Nardowsky (eds.). Fruits of tropical
and subtropical origin. Florida Science Source, Lake Alfred, FL.
*The authors express their thanks and appreciation to Ehud Tzeeri from
Neot-Hakikar, Elaine Soloway from Kibbutz Qetura, Rafi Rotem from the Besor
Experimental Station, David Itzhak from the Ramat-Negev Experimental Station,
Eyal Naim of the Institutes for Applied Research for their skillful help in
this research. This research was partially supported by the following
agencies: US-AID CDR; GIARA-Germany-Israel Agriculture Research Agreement;
Moriah fund and the Israeli Minitry of Agriculture.
Table 1. Plant performance of four-year-old marula treesz.
zValues for height and trunk circumference are means ±SE for 30
|Site ||Height (cm) ||Trunk circ. (cm) ||No. main stems/tree|
yData for plants irrigated with fresh water and those irrigated with
brackish water were combined, since plants of the two treatments did not differ
significantly in size.
Table 2. Characteristics of fruits stored at various temperatures for
zValues are means ±E for 10 fruits. Fruit fresh weight ranged
between 20 and 38 g.
|Storage temp. (°C) ||Skin color ratingy ||Juice content (% of fw) ||Juice acidity (meq/ml) ||Total soluble solids (%) ||Reducing sugars (%)|
|4 ||1 ||---x ||--- ||--- ||---|
|12 ||2.8±0.3 ||33.7±2.1 ||0.21±0.05 ||14.0±1.4 ||0.97±0.04|
|20 ||4 ||47.4±3.2 ||0.15±0.05 ||13.8±1.9 ||1.11±0.03|
yColor was estimated visually using a scale of 1 to 4, where 1 =
pale green, 2= green-yellow, 3 = pale-yellow, 4 = deep yellow.
xFruits remained firm and juice could not be squeezed out.
||Fig. 1. Five-year-old marula tree at Qetura (December 1992), top; marula
fruit showing thick peel and soft fibrous flesh containing nut, bottom.
Fig. 2. Development of new growth at various orchards. The percentage
of the tree canopy covered with new leaves was estimated visually at the middle
of each month on a scale of 0 to 3; 0 = no new growth, 1 = less than 20%, 2 =
20 to 60%, 3 = 60 to 100%.
Fig. 3. Abscission of fruits during the ripening period in three
high-yielding trees at Qetura.
||Fig. 4. CO2 evolution rate (A) and ethylene evolution rate (B) in
abscissed marula fruits stored at 20°C. Each value is mean of 10
Last update September 15, 1997