Stigma Constriction in Pearl Millet, a Factor Influencing Reproduction and Disease

The sequence of events during pollination in pearl millet is described. Four or five hours after pollination with compatible pollen a constriction region located in the fused stylodia, consisting of a collar of parenchymatous cells, becomes apparent. The structural integrity of the constriction region is lost within 6 h of pollination, thereby eventually isolating the ovary from other pollen and also from ovary pathogens which normally enter throught the stigma. The constriction develops in unpollinated gynoecia 4–5 d after stigma emergence, thereby contributing to out-crossing in the protogynous commercial hybrid commonly grown in the semi-arid tropics. The potential significance of a stigma constriction character in a wider botanical context is discussed, particularly as it is a hitherto unrecognized incompatibility barrier.