In vitro germination, storage and microscopic studies of pollen grains of four Ocimum species

Abstract

In the present investigation, pollen morphology and viability of four Ocimum L. species viz. O. sanctum (CIM-Angana), O. basilicum (CIM-Saumya), O. gratissimum, and O. kilimandscharicum were studied. Morphological characters were observed using scanning electron and light microscopy. Pollen of all the four studied Ocimum species have hexacolpate apertures with varied aperture length and width. The exine ornamentation was reticulate and bi-reticulate. O. basilicum has large size (53.9 µm) pollen grains and rest three have medium sized pollen. The viability of pollen was assessed through staining dyes such as 2,5-diphenyl tetrazolium bromide (MTT) and 2,3,5-triphenyl tetrazolium chloride (TTC) and in vitro pollen germination method. O. basilicum possessed maximum viability (92.4%) whereas least viability was found in O. sanctum (38.2%). The maximum pollen germination percentage and tube growth were observed in the semisolid medium gelled with phytagel supplemented with 15% sucrose, 15% PEG, 6.4 mM boric acid and 7.3 mM calcium nitrate. O. basilicum showed the highest germination percentage (90.3%) followed by O. kilimandscharicum (57.1%), O. gratissimum (42.5%) and O. sanctum (25.5%). Pollen of the four Ocimum species were stored at different temperatures viz. 37 °C, + 4 °C, 0 °C, − 20 °C, and − 80 °C for 75 days. The highest pollen germinability of all the four Ocimum species was observed at − 20 °C. This study can be helpful in taxonomic identification of Ocimum species and further utilized in conservation and improvement of different Ocimum species by cross-hybridization breeding programmes.