PALMYRAH

The palmyrah palm belongs to the family Palmae, which is a very ancient family of trees, perhaps older than any other flowering plants.  Fossils of members of the palm family has been recorded dating back to 120 million years. This very ancient ancestory would mean that the form and structure of the present palm trees, is a result of natural selection pressure lasting over millions of years.  As all the parts of the palm are useful, it is known as ‘kalpaga tharu’. Palmyrah is aptly called ‘tree of life’ and has contributed immensely to the people both as food and shelter. Most of the products are made by the traditional methods known to us from time immemorial.

There are two kinds of the palmyrah - the male and the female.  The male and female flowers are held by two different trees, never in one tree.  Both male and female trees produce spikes of flowers but only the female plant bears fruits.  However, both trees are used to tap toddy.  The flowers are small and appear in densely clustered spikes, developing into large, brown, roundish fruits.  The male flowers are smaller than the female flowers. 

Each female palm may bear 6-12 bunches of about 50 fruits per year.  The chief product of the palmyrah palm is the sweet sap (toddy) obtained by tapping the tip of the inflorescence. The leaves are used for thatching roofs, screening as fence, as mats, baskets, fans, hats, umbrellas, buckets, sandals and as writing material.  The wood of a fairly old tree is hard, strong and durable and is generally used for roofing.  The fibre from the stalk is used for making brushes and ropes. The leaf stalk is stronger and used as basket bands and the when the stalk is stripped into thin strips it is called ‘naar’ and used in different ways to tie things.  The seeds, stalks and most part of the wood are dried and used as firewood.  In summary no parts of the palmyrah palm is unused at homes. The palmyrah palm like coconut palm, banana tree and bamboo possess a great value to the people.

The palmyrah is believed to be a native of tropical Africa and grows extensively in the drier parts of India, Sri Lanka, Burma, Thailand, Vietnam, Malaysia and in some parts of Indonesia. In India there is no recognized variety. Very little work has been carried out in biotechnology of palmyrah.

In vitro studies
Micropropagation for mass multiplication of selected high neera yielding palmyrah types from different palmyrah growing regions of India is being carried out by Ponnuswami et al.  Surface sterilization procedures and protocol for the establishment of palmyrah explants in different growth media was standardized. Different explants viz., apocolon shoots, leaf bits, thavan tissue, male flower bud and anthers were used for indirect organogenesis. Shoot tips were used for direct organogenesis. After surface sterilization the explants were inoculated in woody plant media supplemented with 25 mg l-1 adenine sulphate, 1.5 g l-1 activated charcoal, 5 mg l-1  BAP and 0.5 mg  l -1  NAA. Greening of shoots was observed 45-65 days after inoculation. Fan like white coloured leaves emerged 75 days after inoculation. Greening of leaves was observed 90 days after inoculation. Expansion and growth of shoots was observed 90-120 days after inoculation.
In parallel, very tender inner part of apocolon shoots was selected as explants and surface sterilized and then transferred to callus induction media (MS+ 5 mg  l -1  2, 4-D). Active callus growth was observed 50 days after inoculation. Proliferation of calli was observed after four months. Embryogenic calli was observed seven months after inoculation.

Molecular markers
Genetic relationship and diversity in 20 palmyrah accessions based on RAPD markers was reported by Ponnuswami et al. (2008).  In order to distinguish between male and female plants prior to flowering in palmyrah, molecular markers can be used.  They can be utilized to diagnose and select a genotype based on linked DNA markers, long before the phenotype is apparent.  This is particularly important in palmyrah palm, which has a long juvenile period.  The investigation was carried out to identify RAPD markers to differentiate between male and female genotypes, stature and high yielding characters at the earlier stage of growth. Among the twenty different palmyrah genotypes studied with 16 primers, a total of 43 reproducible polymorphic and 14 monomorphic bands were identified and scored as RAPD markers.  Depending on the DNA template x primer combination, 3 – 11 reproducible bands were detected in the 250 – 3200 bp size range. Cluster diagram based on UPGMA showed that all 20 different genotypes grouped into 4 different clusters based on the stature, sex and high neera content.

In another study, 20 palmyrah accessions were analysed using inter simple sequence repeats (ISSR) markers with 21 primers. A total of 130 ISSR markers were scored; of which 65 were polymorphic, equivalent to 47.94% polymorphism. These markers were used to estimate the genetic similarity among accessions using Jaccard’s similarity coefficient, with similarity values ranging from 71.6 to 95.7%. The average number of markers produced per primer was 6.11. For each of the 21 ISSR primers PIC value ranged between 0 and 0.46. Cluster analysis based on ISSR data grouped the 20 palmyrah accessions into two major clusters. PCA based on ISSR data clearly distinguished genotypes similar to the results of cluster analysis.

An attempted identification of RAPD markers linked to staminate and pistillate flowers in palmyrah (Borassus flabellifer L.). The material for the study comprised of 30 male and 30 female leaf samples collected from Kerala (Kasaragod), Karnataka (Mangalore) and Tamil Nadu (Killikulam), 10 males and 10 females from each state.  Total genomic DNA was extracted was extracted from young leaflets using the SDS method.  DNA concentration was determined for each sample spectrometrically at 260 nm. Sex-pooled DNA samples were prepared for bulk segregant analysis by mixing equal quantities of the DNA of 30 male individuals (male bulk) and 30 female individuals (female bulk) separately.  Out of 180 RAPD primers screened, only three (OPBE-12, OPBA-13 and OPA-06) showed polymorphism between male and female sex pools of palmyrah.  This study revealed that the male-specific DNA fragment of size 600 bp produced by the primer OPA-06, was tightly linked to the male-sex locus and would be useful for sex determination in palmyrah.

Though palmyrah is generally dioecious, recently a high yielding monoecious palmyrah palm was located near Rajamundry in Andhra Pradesh. DNA was extracted from leaf samples of the monoecious palm and its seven progenies, staminate and pistillate palms and screened using the male-specific RAPD primer. It was observed that the male-specific band of size 600 bp was present in monoecious palm as well as in six out of the seven progenies tested.   From the results, it was revealed that one progeny is possibly female and the rest may be either monoecious or males. No marker has been identified as yet to differentiate monoecious and males. Perhaps the existence of a single monoecious palm makes identification of a marker specific to monoecious palm, a tedious task.

Palmyrah palm being an unexploited crop of potentiality needs thorough investigation in all aspects of growth and production. Standardization of bio-techniques is necessary for better utilization of natural resources.

Source: Dr.V.Ponnuswami, PhD, PDF (Taiwan), Former Dean & Professor (Horticulture), Horticultural College & Research Institute, Tamil Nadu Agricultural University, Coimbatore