Table of Contents
Benzioni, A., S. Mendlinger, M. Ventura, and S. Huyskens. 1993. Germination,
fruit development, yield, and postharvest characteristics of Cucumis
metuliferus. p. 553-557. In: J. Janick and J.E. Simon (eds.), New crops.
Wiley, New York.
Germination, Fruit Development, Yield, and Postharvest Characteristics of
A. Benzioni, S. Mendlinger, M. Ventura, and S. Huyskens
- Germination Experiment
- Date of Planting Experiment
- Fruit Development
- Fruit Constituents
- Ethylene Treatments
- Fruit Development
- Ethylene Application
- Table 1
- Table 2
- Table 3
- Table 4
- Fig. 1
- Fig. 2
- Fig. 3
Cucumis metuliferus Mey. (the African horned cucumber, kiwano, melano)
is endemic to the semi-arid regions of southern and central Africa, where it is
eaten as a supplement by the local population (Bruecher 1977; Keith and Renew
1968). The plant is a monoecious, climbing annual with staminate flowers
typically appearing several days before pistillate flowers. The ellipsoid
fruit is bright yellow-orange in color when mature and shaped like a short
stout cucumber with many blunt thorns on its surface. The mesocarp is green
and consists of juicy bland-tasting tissue. Cucumis metuliferus is
exported as a speciality fruit from New Zealand, Kenya, and Israel to Europe,
and its market is expanding. Several problems associated with agrotechniques
and fruit quality have emerged in the course of commercialization. Some of the
problems encountered include poor germination, too small fruits at some
locations, rapid fruit deterioration during cold storage under humid
conditions, and failure of fruits to develop the desirable uniform orange
color. In this paper, we report on efforts to improve conditions for
successful germination, the effect of sowing dates on crop development, as well
as fruit ripening in the field and in storage, and the effects of ethylene
application to fruits in order to establish optimum harvest time, storage, and
Percentage and rate of germination were examined at 8°, 12°, 20°,
25°, 35°, 40°, and 45°C. Seeds were placed between two layers of
wet cotton in petri dishes that were scored daily over a period of 24 days for
germination. Germination under saline conditions of 0, 20, 50, and 80 mM NaCl
was examined at 30°C .
Seeds were sown on sandy loess at the Sha'ar Hanegev Experimental Station
(northern Negev, Israel) on Mar. 15, Apr. 15, and June 3, 1988 at a density of
10,000 plants/ha. The field was dripirrigated twice a week at 2 liters/hr,
with amounts calculated to replenish 40% of evapotranspiration till first
flower stage, and 80% thereafter. Cultural measures (fertigation and disease
and pest control schedules) were similar to the local practice for melons. A
single harvest when almost all fruits were ripe (after color break, i.e. when
skin shifts from dark green to pale yellow), was carried out on June 30 and on
Sept. 16 for the first and second sowing dates, respectively. Plants sown in
June failed to produce fruit prior to October and thus, were not harvested. At
each harvest, a 10-m2 plot was harvested from each bed and all
fruits collected and divided according to fruit weight into large (>200 g)
and small (<200 g).
About 65 flowers were tagged and hand pollinated at anthesis. Fruits were
picked 33, 37, 45, 51, and 61 days after pollination (DAP) for determination of
Total soluble solids (TSS), pH, electrical conductivity (EC), and reducing
sugars (Sumner 1921) were determined in the fruit jelly. Pigments were
extracted from the peel by a 4 acetone:5 hexane mixture.
Fruits were picked when whitish green, at about the turning point. Ethylene
was applied by exposing fruits for 24 h to 160 µl ethylene. Treated and
control fruits were then stored at 20°C for two months for further ripening
and samples of fruits were removed periodically for analysis.
Yellow-orange fruits were stored at temperatures of 4°, 8°, 12°,
20° and 24°C. In addition, green fruits at about the turning point were
picked and stored at 20°C. Every week, fruits were evaluated and overripe,
soft, or damaged specimens were discarded.
Optimal temperatures for germination were 20° to 35°C where 95 to 100% of
the seeds completed germination in three to eight days (Table 1). At 12°C,
germination commenced at day 16, reaching a final count of 90% on day 24, and
at 8°C was completely inhibited. At very high temperatures (40° and
45°C) percentage germination was greatly reduced, although enough seeds
germinated to indicate possible genetic variation for heat tolerance (Table 1).
Germination was unaffected by salinity of up to 50 mM NaCl.
March sown plants covered the beds in about six weeks and began to flower and
set fruits in eight weeks. Vines of plants sown on the second date (Apr. 15)
covered the beds only after ten weeks, although here too flowering began eight
weeks from sowing. Fruit development was slower in the April sowing and
although the number of fruits/ha was similar (271,000 versus 245,000 for the
March planting), many fruits were smaller (Table 2). The plants sown on 3 June
failed to grow well, and by the end of the experiment in October had neither
covered the beds nor flowered. The plants of the March sowing yielded over 46
Mg/ha of fruits (Table 2). More than 60% of these fruits were large (>200
g) and would command premium prices in the market. The yield for the second
sowing date was 28 Mg/ha, of which only 25% consisted of fruits classified as
large; nearly half the fruits were very small and of non-commercial size (Table
Maximal fruit weight of 205±;57 g was reached by 33 DAP. The main period of
fruit ripening on the plant in terms of changes in fruit constituents and color
occurred between 37 and 51 DAP (Fig. 1, 2). During this time, both total
soluble solids (TSS) and reducing sugar levels increased in fruits attached to
the plant, peaking at about 50 DAP (Fig 1). The ripening period was also
characterized by changes in the color of the fruit peel, with absorbance of
light at wavelengths of 663 and 431 nm decreasing with time indicating loss of
chlorophyll, and with absorbance at 442 and 470 nm increasing, indicating
carotenoids production (Fig. 2).
Application of ethylene to fruits at the breaker stage resulted in fruits
progressing from green to yellow within three days of treatment (Fig. 3).
Non-ethylene treated fruits took much longer to change color and at day 60
still appeared slightly green and less mature than ethylene-treated fruits.
From the changes observed in the absorption peaks during ripening, it appears
that in ethylene-treated fruits the absorbance at 431 nm disappeared three days
after treatment while it took more than 30 days to fade in untreated fruits.
The decline in the 431 nm peak was followed in all fruits by the development of
a peak at 442 nm (Fig. 3). In some of the ethylene-treated fruits a new
absorption band appeared at 420 nm, and fruits were more orange than yellow.
No absorption at this wavelength was detected in fruits of the control group
(data not presented). The TSS levels remained stable during storage and were
unaffected by ethylene treatment. Reducing sugars of both treated and non
treated fruits rose during storage from 16 to 25 to 30 mg/g fresh weight (Table 3). The rise in reducing sugars during storage was not enhanced by ethylene
treatment and occurred within 12 days of commencement of storage. Electrical
conductivity (EC) did not change during storage, and a decline in acidity and a
rise in pH were observed (Table 3). Fruits from the same experiment allowed to
ripen in the field had a higher final content of reducing sugars on a fresh
weight basis, 42 mg/g vs 25 to 30 mg/g in storage (Table 3).
Fruits picked after the initiation of ripening (yellow color detectable) kept
well at 20° and 24°C. All fruits kept at 24°C and 70% of those kept
at 20°C were still firm and undamaged after three months of storage (Table 4). Cold storage at 4° or 8°C resulted in much shorter shelflife, and at
4°C chilling symptoms in the form of opaque spots on the fruit surface
appeared (Table 4).
The best time for sowing C. metuliferus at our sites would be mid-March
to early April. Fruits require about 35 days to mature green and another two
weeks to full maturity. Ethylene enhances ripening similarly to its effect on
'Honey Dew' melons and its application may be of agronomic use, enabling
growers to harvest at the breaker stage and store fruit for a longer period
(McGlasson and Pratt 1964; Pratt et al. 1977). Fruits could be treated with
ethylene just before marketing to induce a pleasing, uniform orange color on
their arrival at the market.
The fruit has an exceptional long shelf life at temperatures of 20° to
24°C which makes it eminently suitable for development as a new exotic or
ornamental crop. However, further research aimed at breeding or selecting for
tastier genotypes is essential since the present unsatisfactory taste limits
the potential market.
- Bruecher, H. 1977. Cucurbitaceae, p. 258-297. In: Tropische Nutzpflanzen.
Springer Verlag, Berlin.
- Keith, M.E. and A. Renew. 1975. Notes on some edible wild plants found in the
Kalahari. Gemsbok Park. Koedoe 18:1-12.
- McGlasson, W.B. and H.K. Pratt. 1964. Effect of ethylene on cantaloupe fruits
harvested at various ages. Plant Physiol. 39:120-127.
- Pratt, H.K., J.D. Goeschel, and F.W. Martin. 1977. Fruit growth and
development, ripening and the role of ethylene in the `honey dew' muskmelon.
J. Amer. Hort. Sci. 102:203-210.
- Sumner, J.B. 1921. Dinitrosalicylic acid: A reagent for estimation of sugar
in normal and diabetic urine. J. Biol. Chem. 47:5-9.
*This work was supported by the GIARA program file No 864393. We gratefully
acknowledge the excellent technical work of S. Avni and the styling of A. Sen
and I. Mureinik.
Table 1. Germination percentage of Cucumis metuliferus seeds at
eight temperatures and four NaCl concentrationsz.
zGermination tests used 10 seeds and two replications (15 seeds at
30°C for NaCl test)
|Variable ||Days till |
|8 ||--- ||0|
|12 ||24 ||90|
|20 ||8 ||100|
|25 ||3 ||100|
|30 ||3 ||100|
|35 ||5 ||100|
|40 ||20 ||35|
|45 ||2 ||15|
|0 ||3 ||100|
|20 ||3 ||100|
|50 ||12 ||100|
|80 ||24 ||100|
Table 2. Fruit size fruit number and fruit yield of Cucumis
metuliferus at different sowing datesz.
zMean separation in columns by Duncan multiple range test, 5%
| ||Yield (Mg/ha) ||Fruit number (1000/ha)|
|Sowing date ||>200 ||<200 ||Total ||>200 ||<200 ||Total|
|March 15 ||27.9a ||18.5a ||46.4a ||107a ||138b ||245a|
|April 15 ||7.0b ||21.2a ||28.2b ||31b ||239a ||271a|
Table 3. Effect of ethylene (160 ppm), applied for 24 h, on fruit
constituents during storage. Values are means ±SE for 5 to 7 fruits.
|Maturity at harvest ||Storage (days) ||Ethylene trt. ||Fresh wt. (g/fruit) ||pH ||EC (dS/m) ||Acidity (µeq/gfw) ||TSS (%) ||Reducing sugars (mg/gfw) ||Water loss (%)|
|Mature green ||0 || ||225±12 ||4.06±0.02 ||4.82±0.30 ||91±5 ||4.76±0.19 ||16.10±0.70 ||0.0|
|Mature green ||3 ||+ ||198± 5 ||4.15±0.04 ||4.14±0.17 ||96±8 ||4.57±0.21 ||22.08±2.27 ||0.5|
|Mature green || || ||199±12 ||4.22±0.05 ||4.11±0.1 0 ||88±6 ||4.33±0.19 ||19.96±1.02 ||0.8|
|Mature green ||12 ||+ ||234±15 ||4.12±0.04 ||4.09±0.22 ||103±5 ||4.53±0.19 ||28.42±0.96 ||1.3|
|Mature green || || ||202±17 ||4.21±0.06 ||3.72±0.12 ||85±9 ||4.02±0.38 ||21.12±2.60 ||1.4|
|Mature green ||25 ||+ ||214±20 ||4.21±0.05 ||4.22±0.12 ||82±8 ||4.60±0.29 ||30.04±3.50 ||3.3|
|Mature green || || ||219±10 ||4.18±0.05 ||4.14±0.1 6 ||81±8 ||4.93±0.30 ||30.18±4.04 ||2.8|
|Mature green ||61 ||+ ||212±14 ||4.29±0.03 ||3.79±0.49 ||74±2 ||4.40±0.07 ||26.84±1.06 ||7.6|
|Mature green || || ||211± 8 ||4.89±0.05 ||4.11±0.32 ||76±8 ||4.73±0.49 ||25.56±1.88 ||6.6|
|Yellow orange ||0 || ||236±10 ||4.24±0.02 ||3.41±0.14 ||96±3 ||6.19±0.14 ||41.62±3.20 ||0.0|
Table 4. Effect of storage temperature and maturity at harvest on shelf
life of Cucumis metuliferus. At each temperature 24 fruits were scored
once a week; spoiled fruits were discarded.
| ||Spoiled fruits (%) after storage|
|Maturity at |
|30d ||37d ||45d ||55d ||75d ||90d|
|Ripe ||4 ||17 ||89 ||100 ||100 ||100 ||100|
|Ripe ||8 ||25 ||58 ||92 ||100 ||100 ||100|
|Ripe ||12 ||60 ||60 ||100 ||100 ||100 ||100|
|Ripe ||20 ||0 ||30 ||30 ||30 ||35 ||35|
|Ripe ||24 ||0 ||0 ||0 ||0 ||0 ||0|
|Mature green ||20 ||0 ||0 ||0 ||0 ||0 ||0|
|Mature green ||24 ||0 ||0 ||0 ||0 ||0 ||0|
||Fig. 1. Accumulation of reducing sugars and changes in soluble solids
(TSS) in fruits maturing in the field. Fruits were picked at different stages
of development. Values are means ±SE of five fruits.
||Fig. 2. Pigment profile changes in the fruit peel during fruit
development in the field. Values are means ±SE of 5 fruits.
Fig. 3. Effect of 24 h of exposure to ethylene on pigment profiles of
fruits during storage at 20°C. Each value is the mean of 5 to 6 fruits.
Bar indicates the critical range according to the Tukey test.
Last update September 17, 1997