STUDIES ON UNREDUCED GAMETE FORMATION IN HYBRIDS BETWEEN TETRAPLOID WHEATS AND AEGILOPS-SQUARROSA L

Five accessions of Aegilops squarrosa L. were crossed to nine of tetraploid wheat, and 18 combinations of normal F1 hybrids were obtained. Their meiosis and the frequency of unreduced gamete formation were observed. From cytological observations, unreduced gametes were formed as follows; restitution of the first meiotic division, and normal second division followed by formation of dyads which developed into two fertile 2n pollen grains. Unreduced gametes were formed with high frequency in the following cases; (1) when Triticum carthlicum Nevski was used as female and Ae. squarrosa ssp. strangulata Eig or var. meyeri Griseb. was used as male; (2) when spikes headed relatively later; (3) in spikes of secondary or subsequent tillers. The high frequency of unreduced gamete formation in F1 hybrids between T. carthlicum and ssp. strangulata or var. meyeri is genetically controlled.