The Date Palm (Phoenix dactylifera)

Date palm ('Nakhla' in arabic), the tree of life.

 

It is a fruit tree crop that can benefit from applications of recently developed plant tissue culture and plant molecular biology techniques. Slow growth, dioecy (separate male and female trees), the slow offshoot-based propagation system and the impossibilities of predicting adult characteristics of the seedlings have previously restricted rapid improvement of this ancient and most important tree crop.

Distributed throughout the Middle East, North Africa and South Sahel, areas of East and South Africa, SW USA, Central and South America and even in Southern Europe (notably in Spain and Italy) - the total number of date palm trees in the world is approximately 105 million covering an area of 800,000 ha. Date palms have yet to be developed in other suitable areas of the globe in which dry climates are experienced and where there is a desperate need to stabilise and create new sustainable macro- and micro-environments.

In addition to producing a valuable dessert fruit, important biproducts such as building materials and versatile starting materials for handicrafts can be derived from date palm leaves and trunks making it an important multiple purpose tree and a significant earner of foreign revenue for both small and large farmers. The date palm also makes a significant contribution towards the creation of equable micro-climates within oasis ecosystems thus enabling agricultural development to be sustained in many drought- and saline-affected regions.

The nutritional value of the relatively-easy-to-store date fruit is high with sugars comprising up to 70% of the fruit ( in most varieties the sugar component consists of glucose and fructose). Dates are also good sources of iron, potassium, calcium, magnesium, sulphur, copper and phosphorus, along with various vitamins, including thiamine, riboflavin, biotin, folic and ascorbic acid. The fruit play an important role in the daily nutrition of human
populations in the above regions. Its use also as a livestock feed supplement gives the tree much added value. The secondary products generated
from fruits are syrups, jams, ice creams, baby foods, alcoholic beverages and soft drinks. Small- and intermediate-scale industries can therefore be
supported over long term periods in both urban and rural situations. This is reflected in its widely acknowledged sustainability value in social, economic and ecological terms.

Date palm trees are essential integral components of farming systems in dry and semi-arid regions and can be produced equally well in small farm units
or as larger scale commercial plantations. The tremendous advantage of the tree is its resilience, its requirement for limited inputs, its long term productivity and its multiple purpose attributes.

 

For centuries, the propagation of date palms by offshoots was the only
commercial method of vegetative clonal propagation used in date palm growing regions of the world to multiply the best varieties. Offshoots are
produced from axillary buds situated on the base of the trunk during the juvenile life of the palm. However they develop slowly and the numbers produced per tree is limited. They are also produced only within a certain period in the mother palm's life. The low number of transplantable offshoots available in the life time of a selected tree varies from 10 to 30 depending on the cultivar and the cultivation practices used. No field-based methods are as yet available with which to increase the numbers of offshoots produced by each tree. Offshoots have to be large enough (i.e. 10 to 12 kg) to survive when
transplanted in the field, a process of regeneration that can take up to 10 years.

Seed is the most convenient material with which to propagate date palm: seeds can be stored for years, they germinate easily and are available
in large numbers. However, this method can not be used commercially for propagating the cultivars of interest in a true-to-type manner for several
reasons. The most obvious is the heterozygous characteristics of seedlings which is related to the dioecious nature of the date palm: half of the
progeny are generally male, which produce no fruits, and large variations in phenotype can occur in progeny. Furthermore, no method is known at the
present for sexing date palm at an early stage of tree development. It is therefore not possible to eliminate non-productive male trees in the nursery
before plantation on a field scale. Another important drawback of seed propagation is that the growth and maturation of seedlings is extremely
slow. A date palm seedling may take 8 to 10 years or more before fruiting occurs. For all of these reasons, propagation by seed is rarely practised by
farmers and the method is used only in exceptional cases when supplies of offshoots are unavailable and there is an urgent need to provide cover and shade in a given area to prevent desertification.

Date palm breeding is hampered by the naturally long generation cycles of trees. It usually takes more than 30 years to complete three backcrosses and to obtain the first offshoots from an inter-variety cross. To produce sufficient offshoots for testing in the field, many generations are required to characterise gene segregation and if the breeding target is yield or fruit quality even more time is needed as a date palm does not reach full commercial fruit production until 10 years after planting. It is therefore not surprising that little date palm breeding has been achieved using traditional approaches.

 

In order to speed up the progress of date palm clonal propagation and breeding programmes, particularly in those cases where date palms are threatened by devastating diseases like the Bayoud as is the case in some of the Magreb countries in North Africa, biotechnology tools of tissue culture and genetic engineering can now effectively speed up all of the above processes and in addition genetic fingerprinting can be used to generate quicker and more precise analyses of elite clones and varieties, thus taking years off the traditional methods. That is one of the reasons behind the establishment of the informal consultative group on date palm called Nakhlatec which was set up at Wye College during 1995 by Professor Mantell and colleagues to deliver expertise in biotechnology to develop this tree crop. See for example:

 

www.biotech-monitor.nl/3008.htm

 

Biotechnology is not necessarily the only solution but it is one newly available tool that can assist breeders and palm producers improve the qualities of date palm and allow its use in many types of socio-economic, horticultural and agricultural development situations in dry and semi-arid regions of the world. It can help in the following three ways at this point in time:

 

1. Tissue culture cloning by somatic embryogenesis and/or axillary branching techniques can increase relatively rapidly the numbers of clonal plants available for commercial plantation or small scale garden development. The methods have already been proved to work in the Sultanate of Oman, Morocco, United Arab Emirates, France, Spain, Brasil and the United States among other countries. Nakhlatec consultants have been involved in the development of tissue culture cloning tools for date palm in Oman and Morocco. There are of course risks of somatic mutation occurring in large scale tissue culture cloning using somatic embryogenesis. As with any tissue culture cloning process which makes use of somatic embryogenesis based on rapidly dividing meristematic tissues in the presence of strong plant growth regulators, for the initial culture stages at least, deviants (non-clonal individuals) might arise occasionally. The risk of somatic mutation is reduced substantially by using strict tissue culture management procedures in which Nakhlatec has some valuable expertise to offer. A new opportunity which Nakhlatec offers is Rotogro^® Technology which can speed up substantially the weaning of date palm tissue culture plantlets using a revolutionary growing system specially designed to cope with large plant numbers and to impose tight environment management conditions (ie light, temperature, humidity and nutrient delivery are closely regulated and non-chemical pest/disease control ensured) at this critical stage of the plant multiplication process. Plant survival is greatly increased and weaning times can be halved. For details, please contact Professor Mantell at Nakhlatec in Sweden.

2. The application of genetic (DNA) fingerprinting tools like RAPD, AFLP and SSR analyses can indicate the genetic fidelity of palm trees produced by the tissue culture process, ie a reliable form of quality control. Such methods can indicate also which varieties or mother tree lines are more susceptible from a genetic point of view to somatic mutation. Mother trees can also be more definitively characterised at the genetic level thus leading to less wastage of culture resources (labour, culture materials and culture running costs). Date palm plants produced by tissue culture can also be guaranteed to be of a particular variety or originating from a specified mother tree. Nakhlatec consultants were among the first in the world to pioneer the application of these techniques to date palm (eg. Aitchitt, 1995 PhD thesis under Presentations).

3. Genetic fingerprinting tools like AFLP can be extremely valuable in identifying genetic fingerprints associated specifically with a number of important agronomic and plant quality traits such as fruit colour, ripening quality, disease (especially Bayoud) resistance and other important characters in date palm. These traits could therefore be linked directly to genetic elements exposed by AFLP (or other relevant emerging DNA/RNA analytical techniques) so that breeders might better predict the inheritance of characters and so reduce the time taken to develop new commercial varieties of date palm. This approach is referred to as Quality Linked Traits (or QLTs). To speed up QLT usage and effectiveness in date palm (and for that matter any other tree crop) availability of homozygous breeding lines is advantageous if not essential. Anther and pollen culture should now be exploited more than ever to produce haploid and dihaploid materials of the key varieties so that linked inheritance patterns of important phenotypes in date palm could be made more predictable, thereby saving much time, space and labour. Nakhlatec consultants have experience in the above approaches in some crops and can provide significant expertise to get the haploid breeding programmes moving in date palm.

4. In the long term, date palm could benefit from genetic transformation approaches to inserting specific genes which could play an important role in development of date palms resistant to Bayoud and certain troublesome insect pests. Some of the Nakhlatec consultants (listed under Advisors) are actively involved in the development of genetic transformation of palms.

 

Nakhlatec can assist customers in the mounting, logistical preparation, maintenance and evaluation of scientific programmes involving clonal propagation by tissue culture, genetic fingerprinting and genetic transformation of date palm. See About Us and Services.

In summary, Nakhlatec offers a range of technical, scientific and academic services which integrate the biotechnologies of micro-propagation and molecular biology with conventional horticultural expertise and wisdom so to generate appropriate solutions to date palm improvement. Its highly qualified team of Arabic, French, Spanish and English speaking scientists and technicians, many with practical experiences of date palm biotechnology in North Africa and the Middle East, can be contacted through Professor Mantell at the Nakhlatec office in Sweden.