Theor Appl Genet (1995) 91:738-743 9 Springer-Verlag 1995 P. Donini 9 R. M. D. Koebner 9C. Ceoloni Cytogenetic and molecular mapping of the wheat.Aegilops Iongissima chromatin breakpoints in powdery mildew.resistant introgression lines Received: 1 February 1995 / Accepted: 12 May 1995 Abstract The amount of alien chromatin introgressed in eight wheat/Ae, longissima Pml3 recombinant lines, in- volving breakpoints on the short arms of wheat chromo- somes 3B and 3D, was evaluated by cytogenetic and mo- lecular approaches. For each line the residual homologous synaptic ability of the recombinant chromosome in its proximal wheat and distal alien portion was estimated through meiotic analyses. Subsequently, telocentric and RFLP mapping were used to assess the genetic distance from the wheat centromere to the wheat/Ae, longissima breakpoints. One 3B recombinant line was distinguished from the other four by the chromosome pairing and telo- centric mapping analyses. RFLP analysis succeeded in dif- ferentiating the remaining four lines into two groups. Chro- mosome pairing and telocentric mapping of the three 3D recombinant lines suggested that all had distinct break- points. However, the RFLP data could not discriminate be- tween the two more proximal translocations. Physical lo- cations for some RFLP loci were determined by a compar- ison of genotypes and C-banding karyotypes. This showed a considerable expansion of the genetic map compared to its physical length. Key words Alien introgression 9 Homoeologous recombination 9 Telocentric mapping 9 RFLP mapping "chromosome engineering" (Sears 1972) enable the trans- fer of chromosomal segments derived from species with homoeologous genomes, and by 'means of these tech- niques, various chromosomal segments bearing the gene Pml3, which conditions complete resistance to all known races of wheat powdery mildew, have been transferred from the 3S 1 short arm of Aegilops longissima into com- mon wheat, Triticum aestivum cv 'Chinese Spring' (Ceo- loni et al. 1988). The new chromosomal locations of the introgressed segments were determined by monosomic and C-banding analyses to be on the short arm of chromosomes 3B and 3D (Ceoloni et al. 1992). Although C-banded kar- yotyping confirmed that a distal wheat segment had been replaced by one from Ae. Iongissima in all transfers, its precision was only sufficient to estimate the size of the alien segment in those involving 3D. A provisional further estimate of the amount of alien chromatin introgressed in the different recombinants was made by measuring the re- sidual pairing ability of the wheat/Ae, longissima recom- binant chromosomes with their parental homologues (Ce- oloni et al. 1992). In the present paper, we describe a fuller cytogenetic characterisation of the recombinant lines, us- ing a combination of chromosome pairing frequency, tel- ocentric mapping and RFLP analysis. These methods have enabled us to distinguish the translocation breakpoints of certain of the lines. Introduction Utilisation of the wild gene resources of wheat represents a major but as yet relatively little exploited opportunity in genetic improvement. Well-established methodologies of Communicated by G, E. Hart R Donini - C. Ceoloni (~) Department of Agrobiology and Agrochemistry, University of Tuscia, I-01100 Viterbo, Italy R. M. D. Koebner John Innes Centre, Norwich Research Park, Colney NR4 7UJ, UK Materials and methods Genetic stocks Pml3 carrying wheat/Ae, longissima transfers, the isolation and chromosomal localization of which have been previously described (Ceoloni et al. 1988, 1992), were employed in the present investiga- tion. Of a total of eight lines, five (R1A, R4A, R5A, R6A and R1B) 1 involve exchanges between 3S and 3BS and three (R2A, R2B and 1 R1D) between 3S and 3DS. A further 3BS recombinant line (R3A) that was thought, on the basis of its C-banding karyotype, to carry zero doses of chromosome 3A and four of chromosome 3B, of which two are recombinant and two normal (unpublished data), was includ- ed only in some restriction fragment length polymorphism (RFLP) analyses.