Fig. 3

Different pathways of natural 2n pollen production. a Meiosis of normal PMC. After synapsis and separation of the homologous chromosome, PMC developed into a dyad of which chromosome disappeared and nucleus became visible. Chromosome in each cell of dyad had reappeared and then terads were formed after meiosis II. Meiosis in ‘Old Blush’ is the successive type and is asynchronous. b. production process of two types of FDR 2n pollen. One process is PMC with fused spindles that develop into an FDR dyad formed of two cells with a fused nucleus after normal meiosis II, while another process is the development of the vertical spindle into an FDR triad with two 1n cells and one 2n cell from the triple spindle. c. two production pathway of SDR 2n pollen. A dyad formed after normal meiosis I, and then developed into an SDR triad with one binucleate cell and two 1n cells formed from the loss of cytoplasmic division, or abnormal nuclear division caused by the formation of an SDR tetrad with one 2n cell, two 1n cells, and one clear cell