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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).

Germination values for fresh, dry and liquid nitrogen stored pollens



% Germination


% Moisture









































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.

Length of the receptivity period of various date varieties


Receptivity period after spathe opening (days)


Most varieties

8 to 10

Albert, 1930; Pereau-le Roy, 1958

Khadrawy, Zahidi and Deglet Nour


Oppenheimer and Reuveni, 1965

Deglet Nour

7 to 12

Ream and Furr, 1969; Djerbi, 1994



Al-Heaty, 1975


before opening

Dowson, 1982



Dowson, 1982

Bousthami Noire


Djerbi, 1994

Jihel and Ghars


Djerbi, 1994



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.

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