Pollen degeneration in three functional male-sterile lines of eggplant with the wild Solanum cytoplasms

Pollen developing process was studied to identify the stages of pollen degeneration and to elucidate the factors controlling low pollen fertility in three functional cytoplasmic male-sterile (CMS) lines of eggplant 'Uttara'. The CMS lines of eggplant were developed by repeated backcrossing using the cytoplasms of wild Solanum species S. kurzii Brace & Prain, S. violaceum Ort., and S. virginianum L.. Anthers were squashed in 1% aceto-carmine to assess pollen staining ability and pollen degeneration at different stages of development. Unicellular microspores were released from tetrads after normal meiotic division. Pollen degeneration occurred at different stages of pollen development in CMS lines such as at unicellular microspore (29.3-36.3%), early bicellular pollen (5.5-12.2%), and late bicellular pollen (9.3-10.2%) stages. On the other hand, in eggplant, only 3.8% pollen was degenerated at unicellular microspore stage and there was negligible pollen degeneration at other stages. Among the stained pollen, abnormally stained (partly and faintly) pollen were found significantly higher in the CMS lines as compared to eggplant. Well stained pollen was varied from 23.2-31.9% in the CMS lines which was significantly lower than that of eggplant. Number of pollens per anther of CMS lines did not vary significantly from eggplant, except the CMS line with S. virginianum cytoplasm. In vitro pollen germination rate in the CMS lines was found to be significantly lower than that of eggplant. Starch accumulation and hydrolysis during pollen maturation were found incomplete in the CMS lines. Degeneration of pollen in different stages, abnormally stained pollen, incomplete starch accumulation and hydrolysis were most likely causes for low pollen fertility in these three CMS lines of eggplant.