Image analysis of C-banded chromosomes and pairing regionalization in wheat

Abstract

C-banding and image analysis are used to characterize nine somatic chromosomes of wheat and to quantify a series of physical parameters (arm length, heterochromatic band intensity and position) in tetraploid Triticum turgidum and hexaploid T. aestivum wheat. The arm-by-arm meiotic association of the chromosomes at first meiotic metaphase is evaluated with respect to these parameters and genetic pairing regulators. The effect of the genetic factors is analyzed comparatively in homozygous lines or both normal and mutant lines (Ph1/Ph1, ph1a/ph1a, ph1b/ph1b, and ph1c/ph1c) and in aneuploids (ditelo-5BL and nulli-5B–tetra-5D). The pairing values were progressively reduced as follows: 'Chinese Spring' Ph1/Ph1 > 'Chinese Spring' dt-5BL > 'Chinese Spring' ph1a/ph1a > 'Chinese Spring' nulli-5B–tetra-5D > 'Chinese Spring' ph1b/ph1b > 'Cappelli' ph1c/ph1c. The results indicate that although a different contribution to overall pairing exists for each specific chromosome region, the differences in the genetic systems regulating pairing from line to line indiscriminately affected chiasma levels and did not lead to specific deviations in any line. The results seem to show that maintenance of chiasmata at first metaphase of meiosis depends on chromosome length and correlation is strong for the chance of double chiasmata. Moreover, there are indications that some C-bands, particularly in intercalary positions in chromosome arms 4AL, 2BL, 5BS, and 7BL, increase the frequency of chiasma at first metaphase. The pairing intensity in each specific chromosomal segment may be the product of an integrated action of chromosome length, the presence or absence of heterochromatin, and genetic factors.Key words: image analysis, heterochromatin, Triticum, C-banding, meiotic pairing.