| Self pollination of the Chinese Spring plant with a single deletion chromosome produced
a progeny containing 45% of the parental type but failed to produce any disomic deletion
plants. Also when crossed as male parent to Chinese Spring euploid no deletion chromosome
was found in the progeny. Presumably the loss of the major part of 5AL in male gametes
renders them incapable of competing with normal male gametes. However, in the disomic
5R addition containing two 5A deletion chromosomes transmission through the pollen did
occur. Apparently the presence of the 5R homoeologue can compensate for the partial
deficiency of 5AL. In fact this may be the mechanism which allowed such a major deletion
to become established. A large deletion of this type, especially if arising in a male gamete,
would in all probability be selectively eliminated. Two further deletions, although not yet unequivocally identified, have been detected at Cambridge in other addition lines of alien chromosomes to wheat. One is in a 6R addition of King II rye to Holdfast, and is a deletion in the long arm of one of the wheat satellited chromosomes, probably 6B. The other is in the Chinese Spring - Hordeum vulgare addition line C, produced by ISLAM, SHEPHERD & SPARROW (1981). This is the addition line containing the pair of satellited chromosomes which probably belong to homoeologous group 6 and the deletion is in the long arm of a wheat satellited chromosome again probably 6B. It appears that chromosomes with deletions may survive more readily in alien addition lines where the effects of the resulting deficiency are compensated by the presence of an extra homoeologue. A closer investigation of addition lines using more critical techniques, such as C-banding and in situ hybridization of DNA probes, may detect further deletions which are too small to detect by routine cytological screening. Literature Cited GALE, M.D., AINSWORTH, C.C. & BAIRD, S. 1982. Allelic variation at Beta-amylase loci in hexaploid wheat. Proc. 4th Internat. Conf. on Isozymes. (In press). GILL, B.S. & KIMBER, G. 1974. Giemsa C-banding and the evolution of wheat. Proc. Natl. Acad. Sci. (Wash.) 71: 4086-4090. GIORGI, B. 1978. A homoeologous pairing mutant isolated in Triticum durum cv. Cappelli. Mutation Breeding Neswletter 11: 4-5. GIORGI, B. 1981. A line with a deletion on the long arm of chromosome 6B isolated in Triticum aestivum cv. Chinese Spring. Wheat Inform. Serv. 50: 22-23. ISLAM, A.K.M.R., SHEPHERD, K.W. & SPARROW, D.H.B. 1981. Isolation and characterization of euplasmic wheat-barley chromosome addition lines. Heredity 46: 161-174. SEARS, E.R. 1952. Misdivision of univalents in common wheat. Chromosoma 4: 535-550. SEARS, E.R. 1954. The aneuploids of common wheat. Univ. of Missouri, College of Agriculture, Agricultural Experimental Station, Research Bulletin 572. SEARS, E.R. 1977. An induced mutant with homoeologous pairing in common wheat. Can. J. Genet. Cytol. 19: 585-593. SEARS, E.R. and SEARS, L.M.S. 1978. The telocentric chromosomes of common wheat. Proc. 5th Internat. Wheat Genet. Symp. Indian Acad. Sci. New Delhi, 389-407. |
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