Dissimilar behaviour of the two kinds of duplication-deficiency female gametophytes in the T3-6 interchange heterozygote of pearl millet (Pennisetum glaucum (L.) R. Br.)

In structural heterozygotes for the T3-6 chromosomal interchange in pearl millet, the percent pollen fertility correlated with percent seed set. The duplicate-deficient (dp/df) microspores degenerated at binucleate stage. The effect of the dp/df condition on the structure and function of the female gametophyte was investigated in this interchange heterozygote. Inflorescences from the interchange heterozygote plants were fixed at five developmental stages : -at pre pollination (i.e. stage 1) and post pollination (i.e. stages 2 to 5) at 24 hr intervals up to 96 hr after pollination (hap). The embryo sac (female gametophyte) was dissected from the ovule and stained with 2% acetocarmine. In the post pollination samples the rate of early seed development was estimated by counting the number of cells in the embryo and endosperm. A normal looking embryo sac was found in all the ovules at pre pollination stage. Post pollination, two kinds of abnormalities were found in 50% of the ovules : some had unfertilized embryo sacs; some showed a lag in development of the embryo and endosperm. These abnormalities could be due to the dp/df condition of the embryo sacs-the two kinds representing the two types of dp/df products formed in the interchange heterozygote. The difference in tolerance of the dp/df condition on the male and female sides is attributed to a) the (programmed) difference in the control of gametophyte development in the two sexes, and b) the existence of competition among the (three) microspore categories (normal, dp/df of one kind and dp/df of another kind) as opposed to the non-competitive aspect of megaspore development (which ever is the category)