Orderly arrangement of the chromosomes within barley genomes of chromosome-eliminating Hordeum lechleri x barley hybrids

One-hundred and nineteen progeny plants of crosses between one Hordeum lech leri (2n = 6x = 42) accession and the barley varieties 'Wong' and 'Igri' co mprised 54 euploids (2n = 28), 8 hyperploids (2n = 29), 46 hypoploids (2n = 22 - 27), and II polyhaploids (2n = 21). Giemsa C-banding showed most inte rplant chromosome variation to be caused by elimination or, more seldom, du plication of barley chromosomes. The chromosomes of 'Wong' were preferentia lly lost in the order, 1H-4H-5H-3H-7H-2H-6H (5-4-7-3-1-2-6); those of 'Igri ' in the order, 1H-3H or 6H-7H or 5H or 4H-2H (5-3 or 6-1 or 7 or 4-2), ind icating different patterns of elimination. Over years chromosome eliminatio n may be continuous. Hypoploid genomes of 'Wong' had the chromosomes arrang ed in the order, 1H-5H-2H-6H-7H-3H-4H (5-7-2-6-1-3-4), with a discontinuity between chromosomes 1H(5) and 4H(4); whereas in 'Igri' the order was (1H)- 5H-2H-4H-7H-6H-3H-(1H) ((5)-7-2-4-1-6-3-(5)) with a discontinuity at 1H(5), indicating varietal differences. The patterns of barley chromosome elimina tion may be derived from chromosome orders. Elimination starts with a chrom osome at the discontinuity, continues with the chromosome at the other end of the order, and proceeds more or less alternately towards the middle. In hybrids including 'Wong', duplication affected the two chromosomes situated at either end of barley chromosome order. A few older hybrids with 2n = 21 had three or four H. lechleri chromosomes substituted for as many barley c hromosomes suggesting homoeology. Our observations support the hypothesis o f an orderly arrangement of the chromosomes within genomes (Bennett 1981), but they do not agree with the idea of one 'natural karyotype' for each spe cies (Bennett 1984b).