Molecular cytogenetic characterization of Eb-genome chromosomes in Thinopyrum bessarabicum disomic addition lines of bread wheat

Thinopyrum bessarabicum (2n = 2x = 14, (EEb)-E-b = JJ) is recognized for its high tolerance to soil salinity and the scab disease caused by Fusarium graminearum. Seven Triticum aestivum/T. bessarabicum disomic addition lines (2n = 44 = 21 " ABD + 1 " E-b) developed at the International Maize and Wheat Improvement Center were assayed. Genomic in situ hybridization (GISH) showed that six of the seven were true disomic alien addition lines, whereas one was a duplication-translocation addition line in which four-fifths of the additional chromosome was an alien chromosome segment and one-fifth was a wheat chromosome segment. Using AFLP fragments amplified from 32 selective primer pairs, 389 fragments were assigned to T. bessarabicum chromosomes. The duplication-translocation addition line had no unique AFLP fragments but shared 25 fragments with the 7E(b) addition line, indicating that the translocation chromosome probably involved the 7E(b) rather than the 3E(b), as originally described. The presumed 6E(b) addition line was determined to have a pair of 4E(b) chromosomes. Thus, the 3E(b) and 6E(b) addition lines are missing. At present, there are 48 AFLP markers for 1E(b), 67 for 2E(b), 39 for 4E(b), 59 for 5E(b), and 54 for 7E(b). In addition, two RAPD markers for 1E(b), two for 2E(b), six for 4E(b), one for 5E(b), and three for 7E(b) were identified. Sixty-eight AFLP markers were present in the amphidiploid but absent in all tested disomic addition lines, making them putative markers for 3E(b) and/or 6E(b). Also, 50 AFLP and six RAPD markers occur in at least five E-b chromosomes. These molecular markers, when used in conjunction with GISH, will be useful in identifying the two missing E-b addition lines and in monitoring the introgression of E-b chromosomal segments into wheat.