NONRANDOM CHROMOSOME VARIATION AND MORPHOGENIC POTENTIAL IN CELL-LINES OF BREAD WHEAT (TRITICUM-AESTIVUM L)

A cytogenetical analysis of 18 cell lines, 9 microspore derived, 6 ant her derived, and 3 immature-embryo derived, of bread wheat (Triticum a estivum L.) varying in their morphogenic potential was undertaken. Chr omosome variation, both structural and numerical, was detected in all lines studied. Variation was present and, in some cases quite extensiv e, in the earliest samples taken (only 12 weeks after initiation of th e suspensions). Within any culture, the pattern and extent of variatio n changed throughout the course of the study and cells with a euploid constitution generally decreased in frequency with culture age. Among the nine microspore-derived suspensions, morphogenic lines generally s howed a more restricted range of chromosome numbers and higher proport ions of euploid cells than nonmorphogenic lines. The patterns of distr ibution of chromosome numbers among the anther-derived cultures were s imilar to those of the microspore-derived lines but the correspondence between instability and regenerative capacity was less. The immature embryo derived lines, which were neither regenerable nor morphogenic, were all unstable. The anther-derived lines were sampled over several months to determine whether loss of morphogenic potential was related to changes in chromosome instability of specific lines. Analysis of th e ''elite'' line F1.7, initially capable of regenerating green plants, showed that substantial decreases in the frequencies of normal euploi d cells (from 45 to 5%) occurred over the period when morphogenic capa city was lost. However, whether the chromosome instability resulted in loss of morphogenicity or vice versa was not clarified. C-banding ana lyses of lines F1.7 and C82d indicated that instability was not random with respect to the three genomes (A, B, and D) of wheat nor to the d ifferent chromosomes within the genomes. Chromosomes of the B genome w ere most often lost or involved in rearrangements, with breakpoints lo cated at, or near, the heterochromatic blocks. Because of the heteroge neity of the cell lines, extensive analyses of large numbers of cells would be required before it would be possible to determine whether los s of morphogenic potential arises as a result of specific chromosome l oss(es).