Genome relationship between Thinopyrum bessarabicum and T. elongatum: revisited

New meiotic pairing data on triploids and amphidiploids derived from the diploid hybrids between Thinopyrum bessarabicum (Savul. &Rayss) A. Love (2n = 14; JJ) and T. elongatum (Host) D. R. Dewey (2n = 14; J e J e ) are presented, which support the close relationship between the genomes of these two species. Three triploids having the JJJ e genome constitution were analyzed. Two (both derived from backcrossing amphidiploids of T. bessarabicum × T. elongatum with T. bessarabicum) had an averaged metaphase I pairing pattern of 3.89 I + 0.96 rod II + 3.30 ring II + 2.75 III + 0.06 chain IV + 0.01 ring IV in spikes from a field-grown plant and two greenhouse-grown plants sampled in early spring. Another, which was the F 1 triploid progeny of T. bessarabicum × T. elongatum as the result of fertilization of an unreduced megaspore (JJ) by a reduced microspore (J e ), had 3.62 I + 2.16 rod II + 1.34 ring II + 3.28 III + 0.10 chain IV + 0.02 ring IV in spikes of a field-grown plant. The first triploid plant had an averaged metaphase I pairing of 4.60 I + 0.74 rod II + 4.03 ring II + 2.19 III + 0.06 chain IV + 0.01 V in spikes sampled in a warmer greenhouse. The amphidiploids exhibited variable pairing patterns with a wide range of multivalent frequency. It is interpreted that the J and J e genomes are essentially homologous, with difference due mainly to two translocations. A genetic mechanism for a "bivalentization" appeared to be present in most, if not all, amphidiploids and the triploids derived from them. Meiotic pairing patterns reported here for triploid hybrids T. junceiforme (Love &Love) A. Love (2n = 28; JJJ e J e ) × T. bessarabicum, its reciprocal, and T. bessarabicum × T. scirpeum (K. Presl) D. R. Dewey (2n = 28; J e J e J e J e ) also support the conclusion that J and J e genomes are homologous. The network of meiotic data supports the conclusion that J and J e are two versions of the same basic genome.Key words: genome, meiosis, hybrid, amphiploid, bivalent formation.