Synthetic Hybrids of New World and Old World Agropyrons: III. Agropyron Repens X Tetraploid Agropyron spicatum

Three hybrids of A. repens, 2n = 42, × A. spicatum, 2n = 28, and two reciprocal hybrids were obtained from emasculated and unemasculated crosses, respectively. The 35-chromosome hybrids tended to be morphologically intermediate between the parent species but resembled A. repens more closely than A. spicatum. A. repens behaved cytologically as a segmental autoallohexaploid, and A. spicatum acted cytologically as an autotetraploid. Mean chromosome associations of 8.04 I, 12.72 II, 0.41 III, 0.06 IV, and 0.009 V were observed in 116 hybrid cells at metaphase I. Most chromosome pairing in the hybrids was attributed to autosyndesis. A. spicatum, A. repens, and their hybrids were represented by genome formulas of SSSS, R1R1X1X1X2X2, and SSR1X1X2, respectively. Hybrid fertility ranged from 0.02 to 0.69 seeds per spikelet.