Effects of Photoperiod on Microsporogenesis in Biloxi Soybean

Abstract

Three exptl. series of Biloxi soybeans were given photoinductive treatments of 2-10 cycles of 8 hrs. of natural daylight followed by 16 hrs. of darkness. Following induction, series I and II were placed on cycles of long photoperiod consisting of 21 hrs. of light and 3 hrs. of darkness and series III on cycles of 16 hrs. of light and 8 hrs. of darkness. As controls, one group of plants was kept on long photoperiod and never bloomed, a 2d was kept on natural photoperiod and a 3d on short photoperiod. Both latter groups showed normal meiosis and flowered. In all the exptl. groups floral struc-tures developed normally until the differentiation of micro-sporocytes, following which abnormalities in meiosis became apparent. In plants given 5 or fewer photoinductive cycles some microsporocytes enlarged, but vacuolation of cytoplasm and ultimate degeneration of their nuclei occurred, usually before they reached metaphase of meiosis I. In plants receiving 6 or more photoinductive cycles degeneration of sporocytes may occur in some anthers as early as in the preceding, while in others apparently normal meiosis occurs. In some cases degenerative changes may occur before cleavage into microspores occurs, in others cleavage may occur followed by degeneration before micro-spores are matured, but in a few instances apparently normal microspores are formed. None of the plants in the 3 exptl. series ever developed open flowers. The long post-inductive photoperiod appears to have played a significant r61e in bringing about the degenerative changes observed and in suppressing flowering.