PALYNOLOGICAL ANALYSIS OF SOME ACCESSIONS OF MANGIFERA INDICA L. FROM KANYAKUMARI AND THIRUVANANTHAPURAM DISTRICTS OF SOUTH INDIA, INDIA

Smitha. M. V and David Samuel. P. Department of Botany and Research Centre, Nesamony Memorial Christian College (NMCC) Marthandam, Kanyakumari District, Tamil Nadu, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

The pollen morphology of nine accessions of Mangifera indica L were elucidated with scanning electron microscopy (SEM), supplemented by light microscopy (LM) and micrometry. The pollen grains of all accessions were tri-zonocolporate. The shape of the pollen was ranged from sub-prolate to prolate-spheroidal. With regard to exine ornamentation, striate reticulate pattern was the most dominant condition, while striate elongate pattern was rarely observed. Similarly striate reticulate condition with foveolate appearance was also observed in certain accessions. Ectoexine was found to be thicker than endoexine. Exine thickness, colpus length, colpus breadth, apocolpium and mesocolpium were also measured.

Introduction:
The genus Mangifera belongs to the order Sapindales includes the family Anacardiaceae with more than 40 species around the world and 15 species bear edible fruits (Abhishkar Subedi et al., 2008). Mangifera indica L, the king of fruit is one of the high potential fruits and suitable for different agro-ecological zones ranging from sub-humid to semi-arid. Mango tree was reported in Somalia as early as 1331 (Griesbach, 2003). In India the emperor Akbar who reigned in Northern India from 1556-1605 planted an orchard of a hundred thousand mango trees. Because of the fossil records and the presence of plenty of wild and cultivated varieties in India, it was stated that the region of mango origin was most likely Indo-Burma. Vavilov (1926) also suggested Indo-Burma region as the Centre of origin of mango.
Mango has become naturalized and adapted throughout the tropics and subtropics. There are over 1000 named mango varieties throughout the world, with India having the greatest number of over 500, is a testament to their value to human kind (Ian .S.E.Bally.,2006). Pollen, is the most vital unit in the flower biology of plants. The pollen characters are of diagnostic value and of comparative importance in taxonomy and evolutionary considerations at all taxa levels (Nair, 1991(Nair, , 2004 and may be even at the level of individuals in plant population. The importance of pollen in evolutionary schemes of the plant kingdom was first formulated by Wodehouse (1935) and later by several authors (Nair, 1965;Walker and Doyle, 1975;Muller, 1970;Chaloner, 1967). Later a lot of studies have been reported by many authors in different families. Of which one is Solanaceae, it is considered as one of the most advanced family and this fact is confirmed by the tri-zonocolporate nature of pollen grains as reported by many authors, which is similar to the pollengrains of Mangifera indica L.

ISSN: 2320-5407
Int. J. Adv. Res. 6(4), 28-35 29 Very few studies related to mango pollen has been reported, of which one is, a preliminary study of the pollen of Mangifera indica L.cv Haden in South Africa (Esme de Wet and P.J.Robberste, 1986). Conservation of these accessions of mango is essential because they are increasingly threatened in the world. For the conservation of germplasm and their further genetic improvement pollen grain is inevitable resource. In such a backdrop, the present work focuses on the detailed account of the pollen morphological characterization of some accessions of Mangifera indica L.

Materials and Methods:
The polliniferous materials for the present investigation were procured from plants growing in different localities of Thiruvananthapuram and Kanyakumari district. The accessions selected for the study were Kottookonam, Kaarali, Thottu, Selan, Karppurm, Pandi, Kappa, Chunnakannan and Valakkachi. Pollen grains used in the present study were collected from fresh and mature buds of inflorescence and were preserved in 70% ethanol. Further procedure of microscopic preparations was as per the standard method of acetolysis (Erdtman 1952., Nair 1960).
Data on pollen morphology have been generated through LM & SEM studies on the photographs of pollen samples, which revealed the detailed surface ornamentations on the general appearance, which were developed by the magnification by 1000X. In deducting the size of the pollen grains, 20 grains were taken randomly. Parameters such as pollen diameter P, equatorial diameter E, P/E ratio, shape, exine thickness, apocolpium, mesocolpium, colpus length, colpus breadth were recorded. The technical description of the pollen grains was carried out in accordance with the technical terminology used by Punt et al., (2007).

Palynological delineation of accessions of Mangifera indica L:
The observations ascertained that the pollen grains of all the accessions were tricolporate and the exine ornamentation was mostly striate reticulate with muri systematically intertwined into a network. But variations were observed in a few accessions. Although striate elongated condition was noticed in kaarali. Thottu showed striate reticulate condition with striae somewhat elongated. Striate reticulate condition with foveolate appearance was observed in Kappa, Valakkachi and Pandi.
Of the 9 accessions studied the smallest grain was that of Chunnakannan 105 µm, based on P/E ratio and the largest grain was encountered in Kaarali measured at 120µm. Exine thickness varied from 1-2µm thickness. The grains of the accessions was either sub-prolate or prolate-spheroidal. Excrescences was noticed, which was granulate in Valakkachi and bacculate in Karppuram. Microgranules were randomly spread in the colpus region of Kaarali.

Discussion:-
In a Lecture to the Royal Society of London in 1809, Robert Brown pointed out that pollen morphology must not be neglected in plant systematics. The pollen morphology is not affected by environmental conditions, hence it has been used as a reliable diagnostic key in the taxonomical researches (Aytug, 1959). Tomb et al (1974) suggested that 7A 7B 8A 8B 34 pollen characters particularly those of aperture region, are taxonomically useful in subtribe and the acetolyzed material gives more useful information than untreated one.
Pollen shape, aperture type and sculpturing are usually very useful taxonomic characters. Huang (1972) used pollen characters as an additional aid for systematic purposes. Nair (1960) recorded that, the order Sapindales is characterised by the occurance of 3-colporate grains in a great majority of the families composing it. Grains of Mangifera indica L. were larger and have a very small ora compared with those of Mangifera foetida, previously described by Erdtman, 1952. Pollen morphology of mango showed that the grains were triangular in polar view, 3colporate, sub-prolate 29×24µm (exine baculate, regulate A.N.Roa and Y.K.Lee, 1969). The pollen grains of the entire accessions of Mangifera indica L. in the present study were tri-zonocolporate.
The pollen grains are of variable shapes and rises with the size varying from 20-35µm (Singh, 1954).They were generally triangular in polar view and the shape of the grains varied from prolate-spheroidal to sub-prolate, bywhich P/E ratio ranged from 105µm -120μm. P/E ratio is a useful taxonomic character to show a range of variation in different taxa, where Chunnakannan had the lowest P/E ratio (105µm) while the highest P/E ratio was found in Kaarali (120µm). The photographs of pollen samples, which revealed the detailed surface ornamentations on their general appearance were developed, with the dimension ranging from 3000µm -10,000µm.
Earlier investigations of the pollen morphology of Mangifera indica L. revealed that the grains showed striate reticulate ornamentation. In Kaarali striate reticulate condition was absent and instead of that striate elongated condition was noticed. Thottu showed striate reticulate pattern with striae somewhat elongated. But striate-reticulate condition with foveolate appearance was observed in Kappa, Valakkachi and Pandi. Fusion of striae was also observed in some accessions. In Selan fusion of striae was observed at the colpus region. Lateral fusion was very less in Chunnakannan.
There was variation in colpus region, broad and narrow colpus region were noticed in some accessions. The colpi were elongated and boat shaped with acute ends. Bacculate excrescences was observed in Karppuram while in Valakkachi granulate excrescences was seen. Operculum varied in different accessions. Narrow and sunken was observed in Selan. Like ways, wide and narrow operculum was also seen. Exine thickness varies from 1-2μm. Microgranules were randomly spread in the colpus region of Kaarali. Pal, 1992., Pal et at., 1993a, 1993b showed that the taxa having tricolporate pollen grains reveals their advance status whereas taxa with polyad or colpate type of pollen grains shows its primitive status in the evolutionary scale.