Abstract:
Orchidaceae family includes more than 25,000 species, among which Dendrobium
genus is one of the most numerous with over 1,200 species in the world. Orchid
pollen is packaged as pollinia in which the pollen grains are bound together by viscin
threads in masses for effective pollination. Palynological studies of Dendrobium are
more important as orchid pollen cannot be dispersed by wind and carried to the
stigma for effective fertilization but is mostly done by insects and human beings
(hand pollination). Thus, this study was aimed at comparing the efficiency of in vitro
pollen germination and natural pollen germination. In vitro pollen germination of
commercial Dendrobium variety ‘Thailand tommy’and ‘Burania jet green’ was
evaluated using three liquid media containing sucrose (0, 5%, 10%, 15%, 20%) with
0.01% boric acid medium, BK medium containing sucrose, H3B03 (100 mg/L),
Ca(N03)2 (300 mg/L), MgSO4 (200 mg/L), and KNO3 (100 mg/ L) and sucrose
solutions. Pollen were collected from newly opened flowers of two Dendrobium
cultivars, sown on different media and then incubated at room temperature for 24h
and examined under a light microscope (10 x 40). Natural pollen germination on
stigmatic fluid of Dendrobium cultivars was evaluated using hand pollinated
Dendrobium flowers. The pollinia of Dendrobium cultivars were deposited on stigma
of newly opened flowers and after 72 hours the small amount of stigmatic fluid was
stained with cotton blue in lacto phenol and observed under a light microscope (10 x
40). Pollen tube elongation equal or greater than the diameter of the pollen was
considered as germinated pollen. Highest percentage of mean pollen germination was
recorded in 0.01% boric acid containing 20% sucrose medium for both ‘Thailand
tommy’ (16%) and ‘Burania jet green’ (12.50%) while the lowest mean germination
was seen in distilled water medium in ‘Thailand tommy’ (2%) and ‘Burania Jet
Green’ (1.50%) in the in vitro pollen germination process. In natural pollen
germination process, the percentage of mean pollen germination on stigmatic fluid
of Dendrobium cultivars was 26.6% and the pollen tube was elongated 5 times than
the pollen diameter.
