AN ASSESSMENT OF SOME ROOT ANATOMICAL FEATURES OF NINE DATE PALM (PHOENIX DACTYLIFERA L.) CULTIVATORS AT DATE PALM RESEARCH STATION, JHANG (PAKISTAN).
ABSTRACT: Date palm (Phoenix dactylifera L.) is third fruit species in Pakistan while country is the 5th largest producer of in the globe. More than 325 date cultivars growing in Pakistan comprise native and exotic ones which differ widely in morphological and anatomical characteristics. For the purpose, adventitious roots of nine different cultivars from Date Palm Research Station, Jhang were collected and 2 cm piece form each root-shoot junction was placed in formalin acetic alcohol solution. Compound microscope having calibrated ocular micrometer was used to measure the root parameters. It was concluded that all nine cultivars can tolerate mild environmental stresses, had very specific anatomical features which indicate their adoption to a variety of environmental conditions and also play vital role in taxonomic identification of cultivars. The results indicate different evolutionary routes for the date palm cultivars studied which merit further molecular genetic study.
Keywords: Date palm, root anatomy, sclerenchyma area, diversity.
Beginning of date palm (Phoenix dactylifera L.) cultivation exist in the start and considered one of the oldest cultivated plants [1,2]. In Pakistan, a significant increase in cultivating date palm area from 101.81 thousand acres to 180.88 thousand acres, indicating the increase tends in the production, was reported during 1992 to 1994, whereas for the remaining years this increase was slight over time . Among date producing countries Pakistan comes at fifth place with more than 325 date varieties .
Date palm is a monocot, produces fasciculated and mostly fibrous roots. Seeds give birth to the primary roots; from where secondary roots originated. Whereas secondary roots build up the tertiary roots, these are of same type and have approximately same diameter through their length . Water is mainly stored in the cortex tissues of the roots  while wide metaxylem vessels also have the same ability .
Transport capacity of the roots is linked with the root aging and radial growth which results in the increasing number of the xylem vessels  and the diameter of largest vessels .
Aerenchyma formation in the roots of date palm, due to transfer of the cortex, may enhance diffusion of the atmospheric and photosynthetic oxygen from the shoot to roots  . Collapse of cortex can be prevented through the compactness of exodermal and hypodermal layers in the roots and is also an important structural framework for the formation of aerenchyma. Extreme environmental conditions like water potential, air humidity and CO2 during cultivation can cause abnormalities in structure of the root vascular tissues .
Epidermal cells in the roots of date palm may be of spindle, rectangular or hexagonal shape which ranges from isodiametric or elongated with the longitudinal and an oblique elongation into the spindle . Rupturing of the epidermis and proliferations of the sub epidermal cells result into irregular and longitudinal pattern of the white rings of the surface eruptions in all orders of the roots. Proliferated cells have spherical shape, thin walls, highly suberize and many intercellular spaces. Thick walled exodermal cells and outer cortical cells seem as enlarge and undergo into one or two cell divisions which are internally paradermal .
Root structure is extremely imperative in the survival and growth of the date palm and various cultivars of date palm can also be differentiated on the basis of their anatomical characteristics. Keeping the above mentioned facts in mind, the present project was designed and some root structures i.e. epidermis thickness, sclerenchyma cell thickness, cortical region thickness, endodermis thickness and vascular region thickness were studied to differentiate the nine cultivars of date palm, obtained from Date Palm Research Station, Jang, on the basis of their root anatomy.
MATERIALS AND METHODS
Different cultivars of date palm (Phoenix dactylifera L.) not only from all over Pakistan but also from some other countries like Saudi Arabia, Iran, Iraq and Egypt have been cultivated at the Date Palm Research Station, Jhang. Nine different cultivars of date palm from this station were selected to study their comparative root anatomy. A sample of adventitious roots was collected from each cultivar and immediately placed in polythene sample bags. A 2 cm piece form the root-shoot junction was taken for root anatomy and placed in FAA (formalin acetic alcohol) solution (v/v 5% formalin, 10% acetic acid, 50% ethanol and 35% distilled water). After that material was subsequently transferred to acetic alcohol solution (v/v acetic acid 25%, ethanol 75%) for long-term preservation.
Free hand sectioning technique was used for the preparation of permanent slides of root transverse sections. The sections were passed through a series of ethanol grades for dehydration following  methodology. For staining, safranin was used for lignified tissues (sclerenchyma, xylem vessels) and fast green for subrinized and parenchymatous tissues. The sections were finally mounted in Canada balsam for permanent slides and photographed with the help of camera-equipped compound microscope. Measurements of anatomical parameters i.e. dermal, ground and vascular tissues were obtained with the help of ocular micromerter under a compound microscope, which was calibrated with the help of stage micrometer. Data were recorded and comparison of various anatomical structures was made.
Different root anatomical parameters i.e. epidermis cell area, sclerenchyma area, sclerenchyma bundle area cortical cell area, endodermis area, phloem area, pith area and metaxylem area were measured with the help of calibrated ocular micromerter under a compound microscope to compare the different root structures of all 9 cultivars, named as Akhrot, Begum Jhangi, Champa Kali, Chohara, Daanda, Daglut Noor, Dakki, Halawi-1 and Halawi-2 (Table I).
The in detail root anatomical characteristics and comparison of all cultivars are given below,Epidermis cell area Variation regarding epidermis cell area in the date palm (Phoenix dactylifera L.) cultivars was significantly high at p greater than 0.01 (Table 1). Cultivar Deglut Noor and Begum Jhangi showed the maximum cell area (1188.76 mm2), (1188.76mm2) respectively, Cultivar Champa Kali (681.79 mm2) showed greatly reduced epidermal cells. Where Halawi-2 (867.11 mm2) also showed small epidermal cell area.
Sclerenchyma area Sclerenchyma area varied significantly at p greater than 0.001 in all twelve cultivars of date palm (Phoenix dactylifera L.). Cultivar Champa kali (751.71 mm2) showed maximum sclerenchyma cell area (780.5 mm2). The minimum sclerenchyma cell area was recorded in cultivar Halawi-2 (419.56 mm2).
Sclerenchyma bundle area
Sclerenchyma bundle area was significant at p greater than 0.001 in all cultivars of date palm (Phoenix dactylifera L.) except Daanda (Table 1). Area of sclerenchyma bundle varied greatly in all cultivars. Maximum of sclerenchyma bundle area was observed in two cultivars Halawi-1 and Akhrot (19299.97 mm2 and 18671.23 mm2) respectively. Cultivars Halawi-2 (14055.79 mm2) and Dakki (15524.27 mm2) possessed minimum sclerenchyma bundle area.
Cortical cell area
Variations regarding cortical cell area in the date palm (Phoenix dactylifera L.) cultivars were significant at p greater than 0.001 (Table 1). Cultivar Chohara showed the maximum cell area (2534.8 mm2). Cultivar Halawi-2 (1293.65 mm2) showed the minimum cortical cell area.
There was significant variation at p greater than 0.001 in endodermis cell area in all the cultivars (Table 1) of (Phoenix dactylifera L.). Cultivar Chohara showed the maximum endodermis cell area (450.66 mm2). Cultivars Champa kali (314.67 mm2) and Akhrot (314.67 mm2) showed the minimum endodermis cell area.
All the Date palm (Phoenix dactylifera L.) cultivars had significant variation at p greater than 0.001 (Table 1) in phloem area. Cultivars Dakki (4867.02 mm2) and Halawi-1(4807.51 mm2) showed maximum phloem area. Cultivar Champa kali (2989.39 mm2) showed minimum phloem area.
There was significant variation at p greater than 0.001 (Table 1) in pith area in all the cultivars of (Phoenix dactylifera L.). Cultivar Beghum Jhangi showed maximum pith area (42.31 mm2) followed by Cultivars Champa Kali (37.08 mm2). Cultivars Halawi-1, Deglut Noor and Daanda (25.67 mm2) showed the minimum pith area.
Metaxylem area varied significantly at p greater than 0.001 (Table 1) in all the cultivars of date palm (Phoenix dactylifera L.). Maximum metaxylem area was recorded in cultivar Begum Jhangi (18897.50 mm2). Minimum metaxylem vessel area was recorded in cultivar namely Halawi-2 (11361.19 mm2).
Root anatomy of Date Palm (Phoenix dactylifera L.) cultivars planted at Date Palm Research Station Jhang showed significant variations (Table I). The size of epidermis cells, size and shape of outer cortical region, presence of sclerification in outer cortex and endodermal cell area also showed the significant diversity. Cultivar
Akhrot showed two distinct portions of cortical region which were separated by the well developed sclerenchyma. Epidermis was composed of thick walled cells. Distinct sclerenchyma bundles were present in inner cortex. Thick epidermis with intensive sclerification in the cortical region not only prevents the water loss from the roots as  but also provides mechanical strength to the root and this is extremely important under harsh ecological conditions such as drought . Additionally the increased cortical region with densely packed cells, capable of storing additional water and this is vital for surviving under limited moisture environment. This cultivar also showed thick walled endodermis and this is important for checking radial flow of water in the roots .
Epidermis in cultivar Aseel was comprised of extremely large cells and very well developed sclerenchyma in outer cortical region. Outer cortex was composed of very much reduced parenchymatous cells, whereas in larger rounded and densely packed cells. Distinctive sclerenchyma bundles were recorded in inner cortex. Intensive sclerification was also recorded in the vascular region. The variation in parenchymatous cells that is a small tightly packed cells in the outer cortex. Larger cells in the inner cortex with distinctive sclerenchyma region and sclerenchyma bundles may indicate the high tolerance level of this cultivar to variety of environmental condition .
Cultivar Dakki had distinct sclerenchyma region inside the outer cortex with small sclerenchyma bundles in the inner cortex . This cultivar showed large and few metaxylem vessels and intensive sclerification in pith region. This root structure indicated the tolerance of Dakki cultivar to variety of environmental stresses mainly drought, salinity and water logging. This justifies its wide cultivation in the southern KPK province.
Distinctive anatomical features in Chohara cultivar were large root area, large vascular region with intensive sclerification in pith region. Well developed sclerenchyma in the outer cortex. Thick roots are known to be characteristic feature of drought and salt tolerant plant ; this may justify the wide cultivation of this cultivar in Punjab, Sindh and KPK as it can tolerate a variety of environmental stresses.
Distinct modification in the root anatomy of cultivar Deglut
Noor was observed. Very prominent sclerification was recorded in epidermal and hypodermal region. This cultivar was characterized by small aerenchyma and highly sclerified pith region. These anatomical features are typical of xeric nature with the main function of efficient transport of water and prevention of water loss through the roots .
Cultivar Halawi-1 showed poorly developed sclerenchyma in outer cortex and irregularly shaped cells in the inner cortex. Intensive sclerification present in the vascular region. Large phloem area may be responsible for increased translocation of photosynthate . Overall the root structure in Halawi-1 indicated relative sensitivity of cultivar to environmental stresses. This may be the reason of its limited cultivation in Jhang and Faisalabad region.
Anatomical features in Daanda and Halawi-2 were very similar. All these cultivars showed large epidermal cells and distinct sclerenchyma in the cortical region, thick endodermis and intensive sclerification in vascular region. Epidermis along with intensive sclerification in cortex as well as vascular region is characteristics of drought tolerant plants [24,25]. Therefore all these cultivars can be rated as suitable for arid and semi arid regions .
Highly enlarged vascular region with large metaxylem vessel was recorded in Beghum Jhangi and Champa Kali. These cultivars also showed distinctive sclerenchyma in cortical region and prominent sclerenchyma bundles. On these bases it can be concluded that these cultivar can perform better under moderate climate .
Table 1. Root anatomical characteristics of 12 date palm (Phoenix dactylifera L.) cultivars
###Epidermis Scierenchy Scierenchyma Cortical cell Endoderm Phloem area Pith area Metaxylam
Cultivars###cell area###ma area###bundle area Area (p-m2) is cell###(um2)###(um2)###area (um2)
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|Author:||Fatima, Ghayoor; Hameed, Mansoor; Naqvi, Summar Abbas; Shah, Iba Ali|
|Date:||Sep 30, 2012|
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