Division of Horticulture, Indian Agricultural Research Institute, Delhi-12
Meiosis was studied in five species of Annona, viz., A. cherimola, A. glabra, A. reticulata, A. squamosa (Green and Red varieties) and A. atemoya. Excepting A. glabra (2n=28), the taxa studied had 2n=14.
The sequence of the species in descending order of chiasma frequency was found to be as A. glabra, A. squamosa (Green), A. cherimola, A. squamosa (Red), A. reticulata and A. atemoya. This sequence was maintained both at diakinesis and metaphase I.
Meiosis was generally normal, but variable numbers of univalents were. found in a few cells. Nucleolar budding was found in A. atemoya, A. cherimola and A. glabra at early diakinesis stage. Some cells of A. atemoya, A. cherimola and A. reticulata showed an unequal number of chromosomes at each ana-I pole. At second anaphase, both the spindles were observed to lie in one plane instead of being at right angle to each other. Cytokinesis took place by furrowing of cytoplasm.
The occurrence of high chiasma frequency and the absence of multivalents during meiosis have been taken to suggest that the tetraploid species A. glabra is of amphidiploid origin.
