Genome relationship between Thinopyrum bessarabicum and T. elongatum: revisited

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Abstract
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; JeJe) are presented, which support the close relationship between the genomes of these two species. Three triploids having the JJJe 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 F1 triploid progeny of T. bessarabicum × T. elongatum as the result of fertilization of an unreduced megaspore (JJ) by a reduced microspore (Je), 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 Je 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; JJJeJe) × T. bessarabicum, its reciprocal, and T. bessarabicum × T. scirpeum (K. Presl) D. R. Dewey (2n = 28; JeJeJeJe) also support the conclusion that J and Je genomes are homologous. The network of meiotic data supports the conclusion that J and Je are two versions of the same basic genome.Key words: genome, meiosis, hybrid, amphiploid, bivalent formation.

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