CHAPTER VIII: POLLINATION AND BUNCH MANAGEMENT

by A. Zaid and P.F. de Wet
Date Production Support
Programme

I. Pollination

Being a dioecious species in character, date palm sexes are borne by separate
individuals. The unisexual flowers are pistillate (female) and staminate (male)
in character. The male palm produces the pollen and the female palm produces the
fruit. The fl ower stalks are produced from the axils of the leaves in similar
positions to those in which offshoots are produced. The inflorescence consists
of a long stout spathe which, on bursting, exposes many thickly crowded floral
branchlets which are stout and short in male, and long and slender in female.
One adult female palm, on average, produces 15 - 25 spathes that contains 150 to
200 spikelets each. The male flowers are borne single and are waxy white, while
the female flowers are borne in clusters of three and are yellowish green in
colour.

Natural pollination by wind, bees and insects is found to yield a fair fruit
set in various areas of the date growing countries (Marrakech/Morocco;
Elche/Spain; San Ignacio, Baja/Mexico; Ica/Peru, for example). All these regions
are characterised by their 100 % seedling composition with about 50 % males. In
the absence of such natural pollination, female flowers are not fertilised. This
leads to the development of carpels and consequently parthenocarpic fruits
without any commercial value are obtained. Date growers in these areas are aware
of artifi cial pollination techniques, but because of insufficient economic
pressure incentives, such techniques are not applied.

The very old and primitive pollination technique consisted of placing an
entire male spathe in the crown of the female palm and leaving the rest to wind
pollination. According to Chevalier (1930) and Dowson (1961), this technique was
used in Mauritania and Libya, respectively. It has been abandoned because it
could not yield uniformly good fruit sets and requires the availability of large
number of male spathes (Dowson, 1982).

Commercial date production necessitates artificial pollination which ensures
good fertilisation and overcomes disadvantages of dichogamy and also reduces the
number of male palms. The male/female ratio in a modern plantation is 1/50 (2
%). Artificial pollination could be realised according to a traditional method
or by using a mechanised device (Enaimi and Jafar, 1980).

1. Pollination techniques

Depending on the type of pollen available, one of the following three
techniques is used:

1.1 Fresh male strands

The most common technique of pollination is to cut the strands of male
flowers from a freshly opened male spathe and place two to three of these
strands, lengthwise and in an inverted position, between the strands of the
female infl orescence. This should be done after some pollen has been shaken
over the female inflorescence (Dowson, 1982) (Figure 64). In order to keep the
male strands in place and also to avoid the entanglement of the female cluster's
strands during their rapid growth, it is recommended to use a twine (a strip
torn from a palm leafl et or a string) to tie the pollinated female cluster 5 to
7 cm from the outer end.

1.2 Pollen suspension

Laboratory and fi eld experiments on three varieties from Saudi Arabia
(Khalas, Ruzaiz and Shishi) have shown that a pollen grain suspension,
containing 10 % sucrose and 20 ppm GA3 could be used for pollination (Ahmed and
Jahjah, 1985). Pollination sprays were found to be as good as hand pollination
in relation to fruit setting. Similar results were also obtained by Ahmed and
Al-shawaan (1983) who tried pollen grains suspended in 10 % sucrose solution.
Fruit set was 80 % using this suspension technique while only 60 % was obtained
when using the classical hand pollination technique. On the other hand, a
suspension solution containing pollen grains, sucrose, boron, glycerine and GA3
did not match the results of hand pollination (Hussain et al., 1984).

1.3 Dried pollen

This pollination technique is more economical and allows proper use of the
pollen as well as adequate control of the timing of pollination. Dried pollen
could originate from the last season, from early maturing males of the same
season, or from few days old male flowers. There are several techniques to apply
dry pollen:

(a) Cotton pieces: The most common technique of using dry pollen is
to dust it on cotton pieces about the size of a walnut and place one or two
pieces between the strands of female inflorescences.

(b) Use of a puffer: A small manual insecticide duster, known as a
'puffer' is also used to apply dry pollen. This technique is used either alone
or in addition to the cotton pieces technique (Nixon, 1966).

(c) Mechanical pollination: Mechanical pollination was developed
mostly in the New World of date palm (USA and Israel) where labour is
expensive and not always available. It consists of pollinating freshly opened
female spathes from the ground with the use of a special apparatus. Mechanical
pollination has been one of the most important alternatives when the labour
has been reduced by 50 - 70 % (Nixon and Carpenter, 1978; Ghaleb et al.,
1987). It is estimated that a man must climb a date palm eight to ten times
from the time of pollination through to crop harvesting. According to Perkins
and Burkner (1973) all other cultural operations for a 25 ha plantation could
be completed with a labour force of approximately 200 men, whereas pollination
requires nearly 700 men-days during the peak period. Mechanical pollination
from ground level for three times and with 1:4 (pollen/fi ller ratio) was
recommended by Nixon and Carpenter (1978) to achieve high yielding of most
date varieties. It seems that the frequency of mechanical pollination as well
as the suitable concentration of pollen/fi ller ratio are the most important
factors in date palm pollination.

According to Perkins and Burkner (1973), a ground-level duster is capable
of pollinating 24 to 32 ha per season. In order to accommodate the palm height
and also to direct the pollen delivery tube near the bloom area of each palm,
the machine is equipped with a variable height platform capable of 4.5 m
vertical movement. The duster is driven along one side of the date row and
then returns on the opposite side to fi nish the pollination cycle. Such
mechanical pollination will require two labourers and could be realised
according to two approaches:

(i) Pollination of each freshly opened female spathe or;
(ii) Spraying
of the whole female leaf canopy just above the opened
spathes.

The first approach is the more accurate one, but requires the farmer to
have good knowledge of his plantation as well as good record- keeping to
ensure the pollination of all spathes. The second technique is economically
feasible and saves time. However, a high rate of aborted fruits could occur
when this technique is used.

During early season pollination, or when the pollination season is
characterised by low normal temperatures, it is recommended to alternate
pollination of sides of the palm at 4 to 7- day intervals. This overlapping of
pollination was shown to yield more reliable results than full palm
pollination at one time (Nixon and Carpenter, 1978).

There is a trend to use a simple mechanical device called hand pollinator.
It is made of a rubber "bulb", a plastic bottle containing pollen, 5 to 8 m
plastic tube attached to a solid aluminium tube (Figures 65 and 66). By
repeatedly pressing the "bulb", pollen located in the bottle is expulsed with
the produced air and moves through a plastic tube towards the female spathes.
Fruit set resulting from the use of mechanical pollination is usually poorer
than that following hand pollination, but fruit quality and yields are found
to be equal as a result of decreased thinning of the mechanically pollinated
inflorescences. Furthermore, it is worth mentioning that mechanical
pollination requires approximately 2 or 3 times more pollen than manual
pollination. To overcome this problem, date growers are mixing the pollen with
adjuvants, also called fillers, such as talc, bleached wheat flour,
walnut-hull dust with a ratio of pollen/filler 1:9 or 1:10. One gram of pollen
could then pollinate ten female spathes. Adjuvants must present the following
characteristics: their particle size must be similar to the pollen grain with
no harmful effect on the pollen's viability, or its germination on female
stigmates. Hamood and Mawlood (1986) found that repeating mechanical
pollination, 4 times during the season by using 1:10 (pollen/fi ller ratio),
increased the total yield of Zahdi cultivar.

The advantages of mechanical pollination could be summarised as
follows:

* reduction of labour and duration of pollination, both contributing to
the reduction of the cost of pollination. Furthermore, it does not require a
highly trained labour as with the traditional technique;

* ensuring the possibility of pollinating a palm at several times in a
short period of time;

* Allowing the use of a mixture of pollen originating from different
sources, thus ensuring good fertilisation;

* eliminating the risk of accidents occurring as with the old method of
climbing a palm several meters high.

(d) Aircraft pollination: Experiments with pollinating of dates with
an aircraft were conducted in the Coachella Valley of California on Deglet
Nour variety by Brown and Perkins (1972). Results showed that even though
temperatures and weather conditions were favourable, both the helicopter and
fi xed-wing methods of application yielded less fruit sets than the hand
pollination method. This technique was abandoned as it required at least 4 to
5 times the amount of pollen traditionally used, and was also found to be not
economically feasible.

2. Pollen harvest and handling

A male spathe that is ready to split assumes a brown colour and a soft
texture. Immediately after the spathe breaks, the male inflorescence reaches its
maturity and male flower clusters must be cut at this stage. To prevent wind or
bees from causing loss of pollen it is recommended that the freshly-opened
spathe be cut early in the morning.

Date growers traditionally harvest the male spathes one or two days after
their opening and place them in a shaded and moisture-free area for drying
(Figure 67). Strands are then detached and stored till needed for the
pollination of female inflorescences. Transport of strands for a long distance
(between two date plantations) must be handled with maximum care. The use of
paperbags is recommended to preserve the pollen and avoid losses.

The common practice of cutting the male spathe a day or two before its
natural opening as practised in the Old World (Middle East and North Africa) is
not recommended because it requires a high level of experience and familiarity
with the male palms (Nixon and Carpenter, 1978). The technique is to press the
middle or lower part of the male spathe between the thumb and forefinger. If a
crackling noise is heard, it is a sign of maturity of flowers. In such a case
the spathe could be cut and flowers taken to the storage room for drying.

A pollen-handling protocol necessitates the rapid and effi cient dehydration
of moist pollen before its storage.

High temperatures have a negative effect on pollen drying and storing
processes. Pollen exposed to direct sunlight or placed near a source of heat,
will rapidly deteriorate and lose viability (also called vitality) Viability is
defi ned as the ability of a pollen grain to germinate and develop (Gerard,
1932).

3. Extracting, drying and storing pollen

The emergence of many early inflorescences on female date palms before the
opening of an adequate number of male spathes on available male palms always
results in scarcity of pollen. Furthermore, it is well known that, depending on
climatic conditions, a date grower could face a season where a heavy early
female bloom develops. Consequently, the storage of pollen within the
pollination season (2 to 3 months) or from one season to another is a necessity,
mainly for pollen known to have a high metaxenia effect. Date growers should
plant enough males, select the best ones and propagate them in order to meet
their own needs without relying upon other sources for pollen.

Freshly opened male flowers contain a high level of moisture; consequently if
they are not to be used immediately, their prompt drying is important in order
to avoid the destruction of pollen by moulds. As mentioned above, air movement
and sunlight are to be avoided in order to protect pollen viability. There are
various ways and techniques to store the pollen depending on the quantity to be
stored, storage conditions and the duration of storage.

- Storage of strands

It is a simple way to store a small quantity of pollen; strands are
separated and spread in a thin layer on paper in a shallow tray in a
shaded/protected area.

- Male fl ower clusters

Clusters are put on top of screen-wire trays or shelves with a container
beneath to catch the dry pollen that falls from the fl owers; Note that the
pollen quality remains unchanged even though the flowers turn dark within 3 to
7 days. This storage technique is mostly used for handling larger quantities
of pollen.

Date growers in Iraq (Dowson, 1921) and in Egypt (Brown and Bahgat, 1938)
conserve the pollen by placing the flowers, usually dried and crushed, in a
muslin bag and left in a well dried-ventilated area.

- Mechanical pollen extractor and collector

The machine is made of a vertical shaker, a collection barrel, a
cylindrical screen tumbler, a rotating screen disk, a cyclone separator and a
suction fan (Figure 68). The machine can daily handle up to 450 male fl ower
clusters and collects approximately 40 % more pollen than any other extraction
method. The pollen viability and longevity were found to be unaffected by such
mechanical extraction.

Moderate temperatures in a dry room will be satisfactory enough to store
pollen for 2 to 3 months consequently covering the needs during the pollination
season. Pollen storage from one year to the next requires more controlled
conditions and an adequate drying system. Once the pollen is well dried and cold
stored in an airtight container, it could be safely re-used during the next
season with very little loss of viability. Nebel (1939) found that a relative
humidity of 50 per cent and a temperature of 2 to 8°C were the optimum
conditions in deciduous trees for storage of pollen for more than four
years.

Aldrich and Crawford (1941) emphasised the importance of keeping the pollen
as dry as possible during the storage period. To maintain zero per cent
humidity, dry pollen is placed in an open jar within a larger airtight container
(a dessicator) in the bottom of which are well dried lumps of calcium chloride
(Ca Cl2) as a dehydrating agent (Figure 69). Other absorbents that can also be
used are saturated solutions of zinc chloride (ZnCl2), calcium nitrate
(N(CaO)³)²-4H²O) and potassium chloride
(KC1).

Dessicators must then be maintained at low temperatures in a refrigerator
(between 4°C to 7°C) (Aldrich and Crawford, 1941; Oppenheimer and Reuveni,
1967). According to the same authors, approximately 500 g of calcium chloride is
enough for 2 - 3 kg of pollen.

According to Hamood and Bhalash (1987), in order to obtain good fruit set it
is recommended that the stored pollen first be tested for its viability; once
proven the pollen should be mixed with a filler (e.g. wheat flower;
industrialised-non perfumed talc; etc.) at a rate of 1/9 respectively; the
mixture must be prepared immediately before pollination. It is also a good
practice to mix the fresh pollen with that stored for one year.

Cold storage using a common refrigerator (4° to 5°C) or a freezer (-4 to -
18°C) was proven to be satisfactory (Figures 70 and 71). According to Nixon and
Carpenter (1978), lower temperatures under conditions subject to less
fluctuation are safer. As mentioned earlier, the evaluation of the viability of
the pollen, either fresh or stored, is important before the pollination
operation. The use of selected pollen with a high degree of viability will
ensure a better fruit set and consequently an acceptable yield. Pollen could be
dried by lyophilisation using freezing temperatures between -60 and -80°C. Water
is eliminated by sublimation between 50 and 250 mm Hg (Djerbi, 1994).

It was also found that pollen from the date palm could be cryogenically
stored successfully using liquid Nitrogen (-196°C) (Tisserat et al., 1985). The
longest period that palm pollen was treated with liquid nitrogen, was 435 days
(Tisserat et al., 1983). These results suggest that long-term storage of pollen
from the date palm, using ultra-low temperatures, can be used with no
deteriorating effect on pollen viability and on fruit set. Recently, Kristina
and Towill (1993) placed date pollen over a saturated salt solution with a lower
relative humidity (CuSO4 - 5H2O) for approximately 2 hours; the moisture content
was reduced to less that 15 %, and the amount of freezable water in the date
pollen dropped to 5 % making storage in liquid nitrogen feasible (Table 59).

TABLE 59
Germination values for fresh, dry and liquid nitrogen
stored pollens

Pollen

Fresh

% Germination
Dry

LN1

% Moisture

Dry

Date

54

59

29

5

Cattail

2

45-

43

10

Pear

50

47

41

5

Pecan

-

78

61

6

Apple

58

17

27

7

Pine

82

88

84

4

Spruce

87

86

84

9

Maize

45

49

39

12

Source: Kristina and Towill, 1993.

¹ Time in liquid nitrogen storage for these samples ranges from 24 h (maize)
to six months.

² Cattail and pecan pollens were dry when collected: fresh and dry percent
germination values are synonymous.

4. Pollination effi ciency

Pollination of 60 - 80 % of the female flowers is considered satisfactory and
will usually lead to a good fruit set. The pollination efficiency is affected by
several factors and consequently fruit set is highly dependent on these factors.
The pollination time, fl owering period of male palm, the type of pollen, its
viability and amount, and the female flowers receptivity are the main factors to
take into account.

Pollination time

Satisfying pollination results are obtained within 2 or 4 days after the
female spathe has opened. March and April is the normal pollination period in
the Northern Hemisphere; July and August for the Southern Hemisphere. Variety
and season could delay or advance the opening of the flowers.

Flowering period of male palm

Flowering periods of male and female palms should be synchronised in order to
have enough pollen when the female spathes open. It is preferable if the male
spathe opens 2 to 4 days earlier than the female spathe. Hence, male palms
should receive the same cultural techniques as the female palms and must
preferably be planted in areas that receive more sunlight; (i.e. in the northern
hemisphere, their exposure to the south favours, in general, early fl owering).
Lack of irrigation during fall and winter at the northern Negev (Israel) was
found to be the only reason of delaying the fl owering date, and consequently
resulting in low fruit set (Oppenheimer and Reuveni, 1965).

Pollen source and quantity

Studies conducted by Nasr et al. (1986) revealed that seedling males are
highly variable in their growth vigour, spathe characteristics and pollen
quality. Also, the amount of pollen grains produced by spathe varied greatly
from one male to another (0.02 - 82.29 g/spathe). The size of the pollen grain
was also found to vary among males (Asif et al., 1987); Mean diameter of pollen
varied from 16 to 30 microns.

It is well known that different varieties of date palm require different
amounts of pollen (Dowson, 1982). Using fresh male strands, the number required
for pollinating a female spathe may vary from 1 to 10 depending on variety.
Furthermore, some varieties have larger female inflorescences than others, which
require more male strands.

The results of a research experiment conducted at the USDA Citrus and Date
Station (Indio, California-USA) have however shown that all except 3 or 4 of
more than 100 varieties of dates have been pollinated uniformly with
satisfactory results by using only 2 to 3 male strands per female inflorescence
(Nixon and Carpenter, 1978). Applying more strands (when pollen is not scarce)
is considered as good insurance and will have no disadvantages.

Most of the male date palms used throughout the world's date growing areas
are of seedling-origin with a great variation regarding pollen quality. However,
and thanks to the selection programme conducted in various countries, several
male palms were selected and are actually beginning to be recognised as
varieties (Mosque, Mejhool BC3, Deglet Nour BC4, Fard No. 4, Jarvis No. 1, Boyer
No. 11 (USA); Deglet Nour, Hayani and Bentamouda (Egypt and Sudan). There is
however, still room for improvement and a date grower should take into
consideration the following desired characters before selecting and using any
male palm:

* Clusters of the male flowers

The size and number of produced inflorescences per male palm are the first
criteria to look for. Indeed, the more and larger the male inflorescences
available, the fewer palms per ha will be required. As mentioned earlier, the
average pollen bearing capacity of a good male palm should be suffi cient for 50
female palms. The abundance of pollen is determined by both the number of
flowers and the pollen quantity per fl ower.

According to Monciera (1950) and to Wertheimer (1954), good male palms from
Algeria annually produced an average of 740 g of pollen with a maximum of 2,133
g. However, both the number of inflorescences and the weight of pollen of these
palms showed an alternancy phenomenon between high and low yielding years.
According to Djerbi (1994), a good male palm should produce an average of 500 g
of pollen with a regular production over time. Large quantities of pollen do not
however, guarantee the quality of pollen produced and consequently its effect on
the fruit (Metaxenia).

In regions where inflorescence rot occurs (caused principally by the fungus
Mauginiella scaettae cav.), pollen should be taken only from healthy male
palms. Evidence suggests that contaminated pollen may spread the fungal spores
and establish the disease in female palms.

* Metaxenia

It is well known that the pollen not only affects the size of the fruit and
seed (affected more by fruit thinning) but also the time of ripening (Swingle,
1928). Metaxenia is not to be confused with Xenia, which is the effect of the
pollen on the endosperm (embryo and albumen). Metaxenia effect was verifi ed by
several investigations in the USA (Nixon and Carpenter, 1978), in Israel
(Comelly, 1960), in Pakistan (Ahmad and Ali, 1960) and in Morocco (Pereau-leRoy,
1958). The effect of pollen on the time of fruit ripening was proven to be
beneficial and is actually considered as the most important practical
application of metaxenia. Producing and selling date fruits at high prices early
in the season, along with the aim of having more uniform and short ripening
period (avoiding a prolonged harvest) are the two main objectives of using a
selected pollen of high metaxenia effect. A third useful application of
metaxenia is where the development period of the plant is characterised by an
insuffi cient sum total of heat for the fruit ripening of late varieties.

It is worth mentioning that metaxenia effect could also be successfully used
to speed up the fruit maturity and consequently escape the rain damage that is
usually expected at the end of the fruit development period (Algeria, Tunisia,
USA, etc.); The use of the Fard 4 male has advanced the maturation stages of
various varieties all around the world by two weeks. However, under a
summer-rain season, (India, Pakistan, Namibia, Republic of South Africa, for
example) late ripening could be more desirable and the selection of males with
late ripening effect is recommended.

* Male-female compatibility

Usually, a male seedling of a specifi c variety will set better fruits with
specifi c female varieties. Djerbi (1994) observed that some date varieties will
have a better yield if they are pollinated with some males rather than with
others. However, several authors (Monciero, 1954; Pereau-leRoy, 1958) did not
observe any interclonal incompatibility, and fruit sets obtained were always
satisfactory. Pollen of 75 different Tunisian date males with more than 10
female varieties were examined so as to select those that have advanced maturity
and improved date quality (Bouabidi and Rouissi, 1995). Six types of pollen were
proven to be earliness-inducing (DG9, DG4, DF4-1, HF4-1, HF4-3 and HF4-5). Such
a character depends on the female variety with no relationship between time of
maturity and date fruit quality. These results confi rm the fi ndings of
Bouguediri and Bounaga (1987).

As a first conclusion, a test to verify if the pollen of the potential male
is satisfactory for the varieties on which it will be used, is important before
looking into other characteristics.

Pollen viability

The capacity of pollen to germinate and grow normally is known as viability.
The assessment of viability of freshly collected as well as stored pollen is
often desirable before using them for pollination. The pollen from genetically
different male palms have varying viability. Therefore, a viability test can
help in selecting the pollen types which are highly viable. The use of highly
viable pollen is likely to result in more fruit set and higher yield.

Applying enough pollen does not guarantee a good fruit set unless the pollen
used is viable with a high germination percentage. As mentioned earlier, the
evaluation of pollen's viability, whether fresh or stored, is essential before
the pollination operation. The use of selected pollen with a high degree of
viability will ensure a better fruit set and consequently an acceptable yield.
Because of their seedling-origin, different male palms will produce different
pollen from the quality point of view (cf. Metaxenia) and also different
percentages of viable pollen.

Pollen from both the earliest and the latest male inflorescences was found
inferior to that of others on the same palm (Monciero, 1954). The low fruit set
resulting from the use of either the earliest or the latest male inflorescences
could be explained by the non-maturity of their pollen, usually caused by low
summation of heat.

Environmental conditions such as high temperature, low humidity, salinity
build up and UV radiation may infl uence pollen viability.

5. Germination test of pollen grains

In vitro germination allows the measurement of the pollen intrinsic
aptitudes to germinate outside any interaction between pollen and stigma.
Furthermore, pollen capacity to fertilise the ovule and set the fruit is
considered as an estimation of natural intrinsic aptitudes. Hence, in vitro
germination is considered as the most valuable test of pollen viability
(Boughediri and Bounaga, 1987). There are several rapid and reliable techniques
that ensure excellent and fast germination, normal pollen tube growth and almost
no bursting of pollen grains.

Albert's germination technique (1930)

A small amount of pollen grains is dusted on a drop of 20 % sucrose placed on
a cover glass, which is then inverted over a glass cell. A thin fi lm of
vaseline is placed on the top of the cell to seal the cover glass to it. It is
then placed in an incubator at 27°C for 12 to 14 hours and inspection is done
under a microscope. An initiation of a pollen tube growth is considered as
evidence of germination. Germination counts must be taken from 4 fields for each
slide.

Monciero's germination technique (1954)

The medium is a solid and consists of 1 % of agar and 2 to 10 % of glucose;
It is executed at an average temperature of 27°C during 24 hours.

Brewbaker and Kwack's medium (1963)

It is a liquid medium developed in 1963 but modifi ed later by Furr and
Enriquez (1966):. 15 % sucrose, 0.5 g of boric acid (H3BO3), 0.3g of calcium
chloride (Ca(NO3)2. 4H20), 0.2 g of magnesium sulphate (MgSO4) and 0.1 g of
potassium nitrate (KNO3), are added to 1 litre of distilled water. Ten mg of
pollen grains is then added to 50 ml of medium and put in 125 ml Erlen fl ask
and dark incubated at 24 to 32°C. This latter temperature was found to be the
optimum.

The best percentages of in vitro germination of date pollen of various
Algerian cultivars were obtained with 15 % of sucrose and 0.1 % of boron at 27°C
in the dark (Boughediri and Bounaga, 1987). Maximum pollen germination was also
observed at 0.05 ppm succinic acid and 0.5 ppm fumaric acid in a basic sucrose
(20 %) and agar (1 %) medium (Asif et al., 1983).

Tisserat et al. procedure (1983)

Pollen grains are germinated in a liquid medium consisting of 500 mg.l
-1 H3BO3, 300 mg.l -1 Ca(NO3)2.4H2O, 200 mg.l
-1 MgSO4. H2O, 100 mg.l -1 ethylenediamine tertra acetic
acid and 200 g.l -1 sucrose. Ten milligrams of pollen grains is to be
added to 250 ml Erlenmyer fl ask containing 5 ml of the germination medium. The
fl asks are capped with sterilised cotton plugs and incubated at 27 - 28°C for
24 hours under dark conditions. Two drops of germination liquid medium from each
treatment are separately spread on a slide and examined under a light microscope
to obtain the germination percentage. Four random replicates are to be used and
only 100 pollen grains could be examined in each replicate. The emergence of
pollen tube growth is considered as an indicator of pollen germination.

The best medium from all the above for date pollen germination is the modifi
ed Brewbaker and Kwak's medium.

Staining technique of Moreira and Gurgel (1941)

Take a small amount of the pollen grains and place them on a slide with 1 - 2
drops of 1 % acetocarmine solution. The slides are then heated for a few minutes
on a hot plate. Examination is conducted under a microscope at 200 × magnifi
cation power to assess the viability of the pollen grains (use 4 fi elds for
each slide). Pollen grains stained red are considered viable, whereas, the
colourless pollen grains are considered non-viable.

Al-Tahir and Asif (1982) determined the effectiveness and reliability of fi
ve staining agents as indicators of viability of date pollen. A correlation
coeffi cient between pollen staining percentage and germination percentage for 3
(4-5-dimethyl-thiazolyl-2) 2,5 - diphenyl tetrazolium bromide was positive and
signifi cant. A similar technique was developed by Alexander (1969) who was able
to differentiate between viable pollen grains which turn dark red and non
-viable ones which become green.

The above staining techniques are based on the colouring of pollen resulting
from the fixation of some chemical products on a specific cell's components;
Cytoplasmic and enzymatic colouring agents are the two existing staining
products. Within the enzymatic ones we can fi nd 2,3,5 triphenyl-tetrazolium
chlorid (TTC) and 3 (4-(dimethyl-thiazolyl 1,2) 2,5 diphenyl tetiazolium bromide
(MMT), both at a concentration between 0.1 and 0.7 %. These staining techniques,
even though they are easy and rapid, are not recommended because they are not
precise enough when compared to the germination test.

6. Female fl owers' receptivity

Before discussing the receptivity of female fl owers, it is worth mentioning
that the female fl owering period is variety and temperature related and does
not exceed 30 days (El Bekr, 1972). According to Munier (1973), this period is
between 30 to 50 days and could even be longer when the daily average
temperature is low. In the northern hemisphere, it is located during February,
March and April, while in the southern hemisphere it is from July till early
October.

The length of the receptivity period of the pistillate flowers could, in
general, vary up to 8 or 10 days depending on the variety (Albert, 1930; Pereau-
le Roy, 1958). According to Djerbi (1994), the receptivity period for North
African cultivars varies from one variety to another (30 days for Bousthami
Noire, 7 for Deglet Nour, 8 days for Jihel and Ghars and only 3 days for
Mejhool, Boufeggous and Iklane). Beyond these limits, the percentage of
parthenocarpic fruits is higher than 40 %. In Iraq, receptivity of "Ashrasi"
variety was found to be optimum before the natural opening of the female spathe,
while another variety (Barban) until approximately 20 days after the spathe's
opening (Dowson, 1982).

Al-Heaty (1975) found that the stigmas of Zahidi variety have a receptivity
period for 10 days. Oppenheimer and Reuveni (1965), in work conducted on the
varieties Khadrawy, Zahidi and Deglet Nour, found that fruit set declined
signifi cantly when pollination was delayed 10 days or more after the spathe
cracked.

According to Ream and Furr (1969), female flowers of the Deglet Nour variety
do not become receptive for possibly 7 days or more after the spathe cracks.
Further delay to 13 days caused moderate reduction in fruit set and delays
exceeding 13 days greatly reduced fruit set.

Within the pollination period, during which the percent fruit set obtained
does not differ statistically, there was a day on which maximal fruit set was
obtained: in Khadrawi, on the day of spathe crack; in Zahidi, on the day after
and in Deglet Nour, on the seventh day after spathe crack (Reuveni, 1970).
Another interesting fact, especially noted with Deglet Nour, is that the day of
optimum receptivity varies in different inflorescences of the same date
palm.

As mentioned earlier, satisfying pollination results are usually obtained
within 2 to 4 days after the female spathe has opened followed by a second
pollination passage 3 to 4 days later (Table 60). Furthermore, and as a
conclusion, it is well confi rmed that the longer pollination is delayed after
the opening of the spathe the poorer the fruit, set and if more than a week
lapses the yield is usually greatly reduced.

TABLE 60
Length of the receptivity period of various date
varieties

Variety

Receptivity period after spathe opening
(days)

Reference(s)

Most varieties

8 to 10

Albert, 1930; Pereau-le Roy, 1958

Khadrawy, Zahidi and Deglet Nour

10

Oppenheimer and Reuveni, 1965

Deglet Nour

7 to 12

Ream and Furr, 1969; Djerbi, 1994

Zahidi

10

Al-Heaty, 1975

Ashrasi

before opening

Dowson, 1982

Barban

20

Dowson, 1982

Bousthami Noire

30

Djerbi, 1994

Jihel and Ghars

8

Djerbi, 1994

Medjool

3

Djerbi, 1994

7. Effect of environmental factors

7.1 Effect of temperature

High temperatures inhibit the development of spathes resulting in a delay of
the pollination season. Low temperatures, usually early in the season, also have
a negative effect on the fruit set. However, if female flowers open early in the
season and their pollination is essential, then the sets could be improved by
placing paper bags over the female inflorescence at the time of pollination.
Bagging of fl ower clusters early in the season could be practised as an
insurance against poor fruit sets caused by cold weather. Bags must be fastened
in order to prevent the wind from blowing them off. Such bags must be removed
two to three weeks later.

Bagging female spadices using paper bags (40-70 cm) immediately after
pollination and during the first four weeks was found to result in a signifi
cant increase in fruit set, yield and fruit dimensions of Hallawy cv. (Galib et
al., 1988). Furthermore, growth of the pollinated carpels in the bagging
treatment was faster that with the unbagged one.

According to Reuveni et al. (1986), improved fruit set obtained on bagged
inflorescences might not always be attributable to improved temperature
conditions; it probably delays drying of the styles and permits the normal
progress of the pollen tube into the ovule even at relatively low
temperatures.

Efficient pollination is localised within the period when pollen could
fertilise the ovules. It depends on the ovule longevity as well as on the growth
speed of the pollen tube, which is highly susceptible to low temperatures.
During the pollination season, it is recommended not to pollinate in the early
morning or late afternoon, because of the negative effect of low temperatures on
the fruit sets. Ten to 15 % higher fruit set was experimentally obtained when
pollination was conducted between 10:00 a.m. and 03:00 p.m. (Surcouf, 1922;
Pereau-Le Roy, 1958). Laboratory results have concluded that an average
temperature of about 35°C is optimum for pollen germination; lower temperatures
decreased the germination percentage (Reuther and Crawford, 1946).

At locations where daily maximum temperatures during pollination are
frequently less than 24°C, mechanical pollination method is not recommended.
(Brown et al., 1969).

7.2 Effect of rain

There is controversy concerning the effect of rain on fruit set. Some
consider rain that occurs just after pollination as a washing agent that takes
away most of the applied pollen before it plays its role. In such a case, it is
necessary to repeat pollination after the rain has ended. Other people consider
the negative effect of rain on fruit set as an indirect effect via low
temperatures that accompany or follow rain. If temperatures are between 25 and
28°C, most of the pollen tubes reach the base of the style of Hayani variety
flowers within 6 hours (Reuveni, 1986); while at 15°C, pollen tubes do not reach
the base of the style even after 8 hours. A third explanation of the effect of
rain is the reduction of the pistillate fl owers' receptivity by contact with
water. Rain is also responsible for increasing the relative air humidity which
favours attacks by cryptogamic diseases that result in the rotting of infl
orescences. This high relative humidity is also associated with reducing the
pollen's blow out.

In conclusion, date growers must assume that rain can cause all the above
effects, and any pollination operation immediately followed by rain must be
repeated in time. Following pollination experiments conducted at the USDA
research station at Indio, California (Dowson, 1982) and also according to
Pereau-leRoy (1958) there is a limited period (4 to 6 hours either before or
after pollination) during which, if rain occurs, pollination and fruit sets are
affected and the pollination operation must then be repeated.

7.3 Effect of wind

In most date growing areas the latter part of the pollination season is
usually characterised by severe hot and dry wind which dries out the stigmas of
the female fl owers. Cold winds disturb the pollen germination. It seems,
therefore, that dry wind storms lead to a faster drying of the styles before the
pollen tube reaches the ovule. (Reuveni et al.,1986). Wind velocity could also
have an effect on the pollination effi ciency; light wind is beneficial and
favour pollination while high speed winds will take away a great deal of the
pollen, especially for palms found at the edges of the plantation. In some cases
severe wind could also break the infl orescence's fruit stalk (rachis), blocking
the movement of sieve nutrients and fi nally causing the death of the bunch.

Dust storms which leave dust deposits on the flowers during the pollinating
season in the southern parts of Israel, and in California are sometimes
considered to be the cause of poor fruit set.

II. Fruit thinning

Fruit thinning is commonly practised in most date growing regions of the
world in order to benefi t from the following improvements:

a. Avoiding the alternancy phenomenon and ensuring adequate fl owering for
the next season. Thinning will allow the palm to produce regularly each year
rather than to be weakened during one or two years by a heavy production and
causing it to produce small and skinny fruits in the next year;

b. Improving the fruit size and consequently satisfying market
preference;

c. Improving the fruit quality and texture which will refl ect on the
price;

d. Ensuring an early ripening and be first on the market;

e. Early thinning will allow room for the development of the fruit; and
there will be less loss of nutrients (N,P,K.) that have to be replaced by
fertilisation.. Most sources are hence recommending earlier thinning rather
than late thinning.

f. Reducing the weight and compactness of the fruit bunches which will
benefi t the harvesting and packing operations.

Date fruit thinning may be realised at three levels:

(i) reducing the number of bunches per palm (removal of whole bunches);

(ii) reducing the number of strands per bunch (mostly from the central part
of the bunch); and

(iii) reducing the number of fruits per strand (bunch thinning; removal of
a proportion from each bunch).

1. Bunch thinning

Bunch thinning that is based mainly on the cutting back of strands will have
a maximum effect on the size of fruits if applied at the time of pollination
(Nixon and Carpenter, 1978). Cutting out centre strands must wait until the
cluster has emerged further. However, and generally speaking for most varieties,
it is recommended to wait 6 or 8 weeks after pollination in order to apply the
adequate thinning method.

The operation of bunch thinning of the Deglet Nour variety is highly related
to the climate and helps reduce damage due to humidity by a greater air
circulation around the fruits. This ventilation will reduce the risk of later
fruit fermentation, rot and souring. However, with some varieties, the reduction
of fruits per bunch may increase the susceptibility of fruit to checking
(cracking of the fruit skin; minute cracks in the cuticle and epidermal cells)
or blacknose (darkening and shrivelling of the tip). In other climates and with
other varieties, Al Bakir and Al Azzauni (1965) found no pronounced effect of
thinning on the fruit size.

The objective of bunch thinning is to obtain more uniform bunch sizes
depending on the fruit set (removal of fl ower strands if the set is poor and
vice versa). Date growers are advised to take into consideration the variety,
the relative importance of size and local weather conditions before selecting
the thinning method and its degree. Furthermore, the growers should also keep in
mind that:

(i) an overthinning will increase puffi ness and blistering (separation of
skin and fl esh);

(ii) the earlier thinning is practised, the more effective it is in
increasing size;

(iii) large bunches combined with damp weather, will result in fruit rot
and souring;

(iv) whatever technique is adapted, all bunches should be thinned uniformly
in order to obtain uniform size and quality.

By keeping accurate records, a date grower can soon ascertain the optimum
production potential of his palms. Individual palm records would be most useful
in working out an effective policy for thinning. Records of the number of fl
ower clusters formed annually, will assist to ascertain whether the grower is
thinning out too lightly or too severely.

When cutting back the tips and in thinning out the strands, the removal of a
total of about 50 to 60 percent of the flowers or fruits on the bunch has been
found highly desirable. To justify the expense and work involved in thinning
bunches, culture and insect control must be adequate to ensure a harvest of
sound fruit.

According to Nixon (1966), fruit thinning in the bunches of Deglet Nour and
other long- strand varieties is practised differently, depending on the nature
of the bunches of the variety.

Long- strand varieties (e.g.. Deglet Nour)

- Removal of the lower one third or slightly more of the bunch by cutting
back tips of all strands (Figure 72). The total number of flowers on a strand
of average length must be counted in order to determine the desired number to
remove and consequently its equivalent by strand's length.

- Removal of entire central strands in order to reduce the number of
strands in the bunch by one third to about one half on very large bunches
(Figure 72). The total number of strands should be counted to determine how
many are to be cut from the centre. Whole outside strands should never be
removed because the fruit stalk may die.

With other varieties, the technique is commonly modifi ed with respect to the
fi nal amount of dates per strand (20 to 35) and the number of strands per bunch
(30 to 50). An average of 7 to 11 kg of ripe fruit per bunch will be obtained
depending on the original size of the bunch before thinning, the percentage of
fruit set and the amount of thinning.

From experiments conducted by El-Fawal (1972) on an Egyptian variety
"Samany", it would be suggested that the best results may be obtained from a
thinning treatment in which about 40 % of the fruit is removed in two step: the
first is to cut back, at the time of pollination, the tips of strands suffi
ciently to remove about 20 % of the total number of flowers. The second step is
to remove about 20 % of the total number of strands from the centre
approximately 8 weeks after pollination.

Results from Khairi and Ibrahim's work (1983) on fruit thinning of Khastawi
variety (Iraq) concluded that cutting back tips of strands to reduce the initial
fruit load by about 30 % at the time of pollination, and removing weak bunches
with low fruit load at the time of bunch bending six weeks later, is useful
bunch management to produce high fruit quality.

According to Glasner (personal communication), the thinning of Barhee variety
is handled in Israel as follows: At the opening of the spathe, the top 1/3 is
cut and 3 to 4 weeks later the grower will come back to thin another 1/3 from
the inside. This technique leaves 45 to 50 spikelets per bunch, and 20 to 25
fruits per spikelet.

In general, bunch thinning concerns not less than one-half and not more than
three-quarters of the total number of fruits. For most varieties it is generally
desirable to reduce both the number of strands per bunch and the number of
fruits per strand. However, any method of reducing the number of fruits per
bunch will increase the size and weight, and to a certain extent (5 to 10 %)
improve the quality; Furthermore, there is no positive correlation between fruit
and seed weights amongst all thinning experiments indicating that increase in
weight is due to increase in the weight of pulp, but heavy thinning will
increase the susceptibility to checking which will reduce grade.

Short strands varieties (e.g. Hallaway and Khadrawy)

These varieties have shorter but more numerous strands than Deglet Nour.
Consequently, their thinning must focus on the removal of entire central strands
and less should be cut from the tips of the strands. The removal of one-tenth to
one sixth of the strands' tips along with cutting out entirely about one-half of
the total number of strands from the centre of the bunch, has given very
satisfactory results. According to Russel (1931), the number of strands in
Hallaway and Khadrawy varieties should be restricted to 40 to 60 out of 80 to
100 strands by removing the inner ones, and the length of strands should be 35
to 45 cm long by cutting out the ends 7-10 cm. Each strand will then carry 20
fruits (800 - 1200 fruits on each bunch).

Extra large and fancy date varieties (eg.. Medjool)

The Medjool variety, because of its high fruit quality, is the only variety
commonly thinned by removal of individual fruits by hand. Instead of cutting
back strands, only a certain proportion of fruit is removed from the strands.
The fruits of Medjool are so large at maturity that, with a normal set of fruit
many fruits are too crowded to be picked without damage and fruits are often
misformed by pressure from adjacent fruit born on the same strand. According to
Glasner (personal communication), satisfactory results are obtained in Israel by
thinning Medjool to approximately 30 spikelets per bunch. 3 to 4 weeks after
pollination, the spikelets are thinned by hand, leaving only 10 fruits per
spikelet. At the time of harvest, 300 fruits are obtained per bunch with an
average weight of 20 g per fruit. An adult palm bearing 10 to 12 bunches, will
hence yield 60 to 72 kg of high quality Medjool dates.

2. Bunch removal

A regular practice is the removal of entire bunches when their number per
palm is too high. An adult date palm could produce 20 or more fruit bunches. In
fact, if the number of fruit bunches per palm is not reduced to an appropriate
level, the next year's production will be low, and consequently an alternancy
phenomenon is established.

Another advantage of bunch removal is to keep a proper balance between the
number of leaves and fruit bunches. According to Nixon (1966), a Deglet Nour
adult palm, along with other long-strand varieties, pruned to 100 - 120 leaves
(a ratio of eight to nine leaves per bunch) is able to give satisfactory yield
without an alternancy phenomenon.

The number of fruit bunches for a palm to carry safely is dependent on its
age, size, vigour, variety and the number of good green leaves it carries: None
for the first three years (at this age, growth is more important than fruit
production until the palm is well established); one or two in the fourth year,
three or four in the fi fth year and so on.

Depending on variety and growing conditions, full production accompanied with
the maximum number and size of leaves is usually reached at 10 to 15 years and
then about 10 bunches per palm can be allowed.

Bunch removal is practised immediately after fruit set. Priority, of bunches
to remove, should be given to the following:

- bunches with a poor fruit set;

- early and late bunches: generally are small, poorly pollinated and
located at the lower and higher position of the inflorescences production
level;

- bunches that are high in number on one side of the palm (their removal
will ensure equilibrium for the palm); and

- bunches with snapped fruitstalks or broken strands.

Fruitstalks of bunches to remove must be sharply cut at their base (departure
point from the stipe); the operation is usually performed with a single cut,
since the fruitstalk is relatively tender at this stage.

3. Leaf-fruit bunch ratio

An adult Deglet Nour palm, pruned to 100 - 120 leaves, is able to annually
carry 12 to 15 moderately thinned fruit bunches without any alternancy
phenomenon; the leaf-bunch ratio is 8 to 9 leaves for each fruit bunch (Nixon
and Carpenter, 1978). Similar results were obtained with Zahdi cultivar in Iraq
(Hussain et al., 1984). A grower is advised to take into account the variety,
the state of his palms and existing cultural conditions before determining which
leaf- bunch ratio to adopt.

It is worth mentioning that it is a complicated operation since the value of
the leaf to the palm declines with age and no two leaves are of the same age.
Furthermore, leaves 4 years old are only about 65 percent as effi cient in
photosynthesis per unit of area, as leaves 1 year old (Nixon and Wedding, 1956).
Under good cultural conditions, a leaf can support the production of 1 to 1.5 kg
of dates. Regardless of the leaf-bunch ratio, several factors may affect fruit
production: i.e. lack of fertilisation and insuffi cient irrigation which may
reduce the number of fl ower clusters and limit the bearing capacity of the
palm.

How to determine the number of leaves per palm

Leaves are grouped in 13 nearly vertical columns, spiralling slightly to the
left on some palms and to the right on others. The grower must only count the
number of leaves in one of these columns and multiply by 13. According to Nixon
and Carpenter (1978) and in order to allow for uneven pruning at the base,
counts could be made on opposite sides and divided by two (Chapter 1; Figure
4).

4. Bunch lowering and support

With most commercial date varieties, after the pollination season, the
bunches are pulled downwards through the leaves, gently enough not to break any
of the strands, and the bunch fruitstalk is tied for support to the midrib (leaf
rachis) of one of the lower leaves to avoid breaking. This operation is executed
when the fruitstalk is fully extended (long enough) but still fl exible to
permit some of the curvature to be distributed, so that the base will not take
all the stresses. This also makes the bunch easily accessible for thinning,
bagging and/or pesticide application.

Tying could be done with twisted frond leafl ets, with rope or with twine
(Figure 73). It also prevents damage caused by scarring and shattering of the
fruits during high wind, and lessens the later danger of fruitstalk breakage by
supporting the bunch as the weight increases (Nixon and Carpenter, 1978).

After the pollination season, some of the smaller and later bunches are not
always old enough to tie when the earlier and larger bunches are ready for such
an operation, and could thus be tied 3 to 4 weeks later. In general, the
fruitstalk grows rapidly during the first few weeks after pollination and shows
pliability and high bending capacity. When elongation ceases, breakage and
obvious loss of the fruitstalk is to be expected (Figure 74). Usually, the bunch
does not require support until the fruit has attained about 3/4 of its full
size. When the fruit bunch ripens, it could quite easily reach a weight of 35 kg
or more. It is worth mentioning that bunch management of soft date varieties
should receive more attention than that of the dry date varieties.

With young palms, bunches are held off the ground by attaching the fruitstalk
to one end of a wooden stake (with a fork shape, called pole) (Figure 78).

5. Bunch covers

Date palm bunch covers offer several advantages and are commonly used in the
New World of date culture areas in order to protect fruits from high humidity
and rain, from bird attacks and also from damage caused by insects.

Protection from high humidity and rain

In various date growing areas (USA, Algeria, Tunisia, etc. in the northern
hemisphere; and in Namibia, RSA in the southern hemisphere), rain could coincide
with the ripening season and consequently causes severe loss of fruit. A sturdy
light-brown craft-paper is used in the USA to cover and provide good protection
of the bunch during the ripening season (Figure 32).

Protection is applied to the bunches in late kimri stage. Paper covers,
wrapped around the bunch and tied to the fruitstalk, could be used in
combination with a pesticide programme because the lower part of the bunch is
not covered. Covering bunches too early may lead to the sunburning of the outer
young fruits, once the cover is removed.

With varieties such as Khadrawy and Hallawy having a relatively open crown,
white paper covers have been found to cause less sunburn than brown paper
covers. Medjool bunches are usually protected with a lightweight white cotton
bag of which the upper portion is water-proof. Plastic bags are to be avoided
because of sunburn and heat damage to the fruit as well as build up for
humidity.

Wet weather resulting from very high humidity and/or from rain will produce
various levels of damage depending on the fruit ripening stage:

Immediately before the Khalal stage, minute superficial breaks, or checks in
the fruit skin occur. The abundance of these checks and their types (transverse,
longitudinal or irregular) vary in different varieties. When the checking is
severe it is usually followed by a darkening and shrivelling of the tip
(blacknose).

At the Khalal colour (yellow to red), checking no longer occurs and water
will produce deeper and longer breaks or cracks (splitting phenomenon) in the
skin and fl esh beneath. Furthermore, humid weather during the Khalal stage also
favours the attack by various fungi causing serious spoilage from rot.

At the Rutab stage, moisture no longer causes skin breakage, but the fruit
absorbs moisture and becomes sticky, less attractive and more diffi cult to
handle. High moisture content of the fruit will result in fermentation and
souring that often results in heavy losses.

At the Tamar stage, high humidity and rain cause little damage to the fruit
except when it is neglected. The timing of bunch protection from rain is usually
when the fruit starts to acquire its Khalal colour. An early covering will
increase checking and blacknose because it reduces ventilation within the bunch.
Although, the fruits escape damage by actual wetting, damage by excessive
humidity increases.

Protection from birds

Birds of various species cause severe damage by eating on the fruit during
the Rutab and Tamar stage (Figures 75 and 76). Parrots, besides eating the
fruits while on the bunches (mostly at the Khalal stage), kick the fruit off the
bunches with their legs, resulting in the loss of date fruits that fall to the
ground.

Bird attacks are common in Sudan, Sahel countries and also in the southern
hemisphere (Namibia, Republic of South Africa, for example). The most common
birds causing damage to date fruit in Namibia and RSA are the Redbilled Quelea
(Quelea quelea), Redheaded Finch (Amadina erythrocephala), Lesser
Blue-Eared Starling (Lamprotornis chloropterus), and the Redeyed Bulbul
(Pycnonotus nigricans). The Grey Lourie (Corythaizoides concolor),
Rupell's Parrot (Poicephalus rueppellii), and the Rosyfaced Lovebird
(Agapornis roseicollis).

When there is danger of severe bird or/and parrot damage, it is advised to
initiate a bird control system. With the paper bags, the bunch should also be
protected beneath with a good grade of porous cloth or netting that will exclude
birds and insects, but at the same time not interfere seriously with ventilation
of the fruit.

The importance of ventilation increases during the later stages of fruit
growth and ripening as well as with the frequency of showers and periods of high
humidity. If such conditions occur, it is advised to use a cover flared out and
not extending down around the sides of the bunch. The thinning of
central-strands of a bunch will promote better aeration of fruits. Rings or
spreaders 15 to 30 cm in diameter, made usually of heavy wire, could be inserted
in the centres to keep the bunches open as the fruit becomes full sized. Such
accessory is mainly recommended with short-strands varieties, bearing fairly
soft fruits. Those of a many-pointed star shape (or corrugated wire) remain in
place better than circular ones and they must be inserted before the fruit
reaches the Khalal stage.

Protection from insects

The bags retain the fruit and provide some protection from birds, but they do
not hinder fruit-infesting insects (Carpenter, 1981). Unless only Khalal fruit
is harvested, insects may damage more than 50 % of the Rutab fruit. Stored dates
from such palms will show large infestation by living and dead insects.

Physical exclusion of most insects by use of screen bags is a practical
measure used in various localities in the Middle East (Carpenter, 1975). Moths
and other insects larger than fruit beetles (Nitidulidae) are excluded.
The bags are of flexible 18 × 20 mesh wire or shade net (80 % is recommended)
and are 1.0 to 1.5 m2, depending on the bunch size to be covered
(Figure 77). It is closely tied to the fruitstalk to ensure that rain water will
not enter and also to prevent it from being blown away by wind. The best timing
of its placement is mid-to-late chimri stage.

The date grower is advised to conduct proper insect control in the field,
followed by prompt fumigation of fruits immediately after harvest. Packing house
sanitation is closely related to field insect control. The packing facility
should be insect-free to prevent re-infestation of fumigated fruit by "Dried
fruit-infesting insects", flies, roaches and other pests.

Furthermore, the bags eliminate the need for pesticides on fruit and thus
maintain biological control of Parlatoria scale and other insects.

6. Leaf pruning

To avoid confusion, one should differentiate between pruning in general terms
and pruning in date palm. Pruning in fruit trees and bushes of temperate fruit
consists of the removal of living wood, while pruning in date palm is in general
the removal of only dead, or nearly dead fronds and their bases (Figure 79).
Depending on variety and cultural conditions, date palm leaves can remain alive
for at least seven years with a maximum activity during the first year and an
ultimate decrease in their photosynthetic capacity. As the leaves do not drop of
their own accord, they must then be cut off.

Pruning is desirable in order to improve date fruit quality and also enhance
the bearing capacity. In fact, when too many leaves (as many as 180 leaves/palm
unpruned for 5 to 6 years) are retained and reaching below level of the fruit
bunches, a high percentage of fruit affected with checking and blacknose and of
fruit in the dry grades is obtained. Checking, occurring during mid-summer,is
increased by high relative humidity caused by lower leaves. Furthermore, such
lower leaves probably compete with the fruit, and create favourable sites for
diseases and pests. Removing the leaves up to about the point where the lower
ends of most fruit bunches are exposed is highly recommended for adult full
bearing palms.

Pruning is mainly practised after fruit harvest; Pruning could also be
realised at any convenient time between the harvesting and the flowering season
(thinning period is recommended) and because of the greater ease in cutting, it
is desirable to remove them before the bases became hard and dry. The dry, old
hanging and withering or diseased leaves are cut along with superfluous
offshoots. Leaf pruning could also be synchronised with tying down of bunches or
with bagging. It is recommended that leaves which are still green are not pruned
so as to take full advantage of photosynthesis. Considerable evidence shows
that, other conditions being equal, the fruit bearing capacity of a date palm is
in proportion to the number of green leaves it carries.

During the pruning operation, unwanted offshoots should also be removed to
foster growth of those that are retained on the palm for propagation, to make
access to the palm easier and to promote growth and bearing of the parent palm.
In very dense offshoots growth, some of the small plants may be seedlings rather
than true offshoots, and must be discarded.

However, where there is any fear of frost in the coming winter, no pruning is
recommended and the leaves are left for the protection from the cold of the
young tender leaves.

7. Dethorning:

Another important pruning process is the removal of spines, also called
thorns. It is advantageous to annually remove spines from the base of new leaves
in order to facilitate pollination and handling of fruit bunches. Cut thorns
themselves are a source of some danger, because they lodge in leaf bases on the
soil where they persist as a hazard.

Date spines are usually removed from the new growth of fronds in the crown of
the palm just before the pollination season to allow easy access to the date
spathes as they emerge. If the palms have been dethorned the previous year, the
new growth will be 2 or 3 rounds of fronds, each round developing 13 new leaves,
a total of about 26 to 36 fronds to be dethorned. Such an operation will ensure
a safe approach to the spathes for their pollination and also avoid any risk of
injury to labourers during other technical practices (tying down, protection of
bunches, harvesting, etc.)

It is common to use dethorning knives of various designs to remove these
spines: a long sharp curved blade or pruning knife mounted on a wooden handle 30
to 45 cm long, or a sickle type blade with a sharp cutting edge.

Figure 64. Pollination technique using two to three male
strands.

Figure 65. Hand pollinator in use in Zagora, Morocco.

Figure 66. Scheme to show various components of the hand
pollinator

Figure 67. Drying of male spathes in a shaded and
moisture-free area

Figure 68. Mechanical pollen extractor and collector

Figure 69. Dessicator used for long term pollen
storage

Figure 70. Storage of date pollen at low temperatures: (-4°C
down to -18°C).

Figure 71. Even at low temperature storage, a dehydrating
agent (calcium chloride) is needed.

Figure 72. Thinning methods:

A - Removal of the lower one third of the bunch

B - Removal of entire central strands.

Figure 73. Bunch support using a twine.

Figure 74. Breakage of non- supported bunch

Figure 75. A non-protected fruit bunch showing the damage
caused by birds.

Figure 76. Fruits damaged by birds that eventually dry out
and fall on the ground.

Figure 77. Shade net bags used to protect date fruit from
birds and insects attack, (Right: 60 % and left 80 %).

Figure 78. Support of bunches on a young date palm using a
fork shaped wooden stake.

Figure 79. Pneumatic tool used for leaf pruning and fruit
bunches harvest.