CHROMOSOME CONDITIONS IN THE SECOND AND THIRD GENERATIONS OF PENTAPLOID WHEAT HYBRIDS

1930 ◽  
Vol 2 (2) ◽  
pp. 162-170 ◽  
Author(s):  
J. A. Jenkins ◽  
W. P. Thompson
Keyword(s):  
Common Wheat ◽  
Germ Cells ◽  
Chromosome Numbers ◽  
Wheat Hybrids

The numbers and mating capabilities of the chromosomes were determined in a good many F2 plants and their offspring in two crosses between common (42-chromosome) wheat and emmer (28-chromosome) types. In general the results confirmed those of Kihara and supported his conclusions. Chromosome numbers were much nearer those of the parental types than was to be expected if all germ cells were capable of functioning and all zygotes of developing. A large number of expected chromosome types did not appear at all. A high percentage of F2 had only 14 bivalent chromosomes and zero to seven univalents. These tended to revert rapidly to the 14-bivalent condition of emmers. F3 in this group did not have more than 14 bivalents nor more univalents than their F2 parents. A chromosome formula for all of the group of F2 with more than 14 bivalents may be written (14+x) bivalents +(7−x) univalents. Thesetended to revert to the 21-bivalent condition of common wheat. F3 in this group did not have fewer bivalents nor more univalents than their F2 parents. Occasional plants were exceptions to these rules.

STUDIES ON THE FAILURE OF HYBRID GERM CELLS TO FUNCTION IN WHEAT SPECIES CROSSES

1932 ◽  
Vol 6 (4) ◽  
pp. 362-373 ◽  
Author(s):  
W. P. Thompson ◽  
J. M. Armstrong
Keyword(s):  
Germ Cells ◽  
Chromosome Numbers ◽  
Pollen Grains ◽  
Wheat Species ◽  
Experimental Conditions ◽  
Degree Of Reduction ◽  
Random Segregation ◽  
Nuclear Development

Chromosome numbers were determined in numerous male gametophytes of F1 between 21- and 14-chromosome species of wheat. The results show that pollen grains with various chromosome numbers from 14 to 21 are actually formed and in approximately the theoretically expected proportions. The lack of plants in later generations which should result from the functioning of pollen grains with intermediate numbers is therefore not due to the failure of such grains to be formed because of a lack of random segregation at the second reduction division.Grains with intermediate numbers are retarded in their nuclear development, so that counts made on stamens in which division is most active give a smaller proportion of grains with intermediate numbers and a higher proportion with parental numbers than is expected theoretically. Retardation in nuclear development is correlated with a deficiency in cytoplasmic contents, 10 to 15% of the grains showing little or no cytoplasm, and another 15 or 20% showing some degree of reduction in cytoplasm. AH grains with reduced cytoplasm and some of those with normal contents are so retarded in nuclear development (having only one or two nuclei or no organized male cells) that they could not function when the normal ones are mature and the stamen dehisces. Unfavorable chromosome conditions in grains with intermediate numbers cause a complete abortion of some grains and retardation of nuclear development in others.Under the best available experimental conditions only 11 or 12% of F1 pollen grains germinate, in contrast to 70 or 80% for parental pollen. No grains with reduced cytoplasm germinate, and at least 50% of those with apparently normal cytoplasm fail to germinate.

scholarly journals Chromosome Stability of Synthetic-Natural Wheat Hybrids

2021 ◽  
Vol 12 ◽  
Author(s):  
Laibin Zhao ◽  
Die Xie ◽  
Chaolan Fan ◽  
Shujie Zhang ◽  
Lei Huang ◽  
...  
Keyword(s):  
Common Wheat ◽  
De Novo ◽  
Recombinant Inbred Lines ◽  
Chromosome Instability ◽  
Wheat Variety ◽  
Chromosome Variation ◽  
Synthetic Wheat ◽  
Species Evolution ◽  
Wheat Hybrids

Primary allopolyploids are not only ideal materials to study species evolution, but also important bridges in incorporating genetic diversity of wild species into crops. Primary allopolyploids typically exhibit chromosome instability that a disadvantage trait in crop breeding. Newly synthesized hexaploid wheat has been widely used in wheat genetics and breeding studies. To better understand the cytological and genetic basis of chromosome instability, this study investigated the chromosomes of a large number of seeds derived from the synthetic wheat SHW-L1 and its hybrids with natural wheat. SHW-L1 exhibited persistent chromosome instability since we observed a high frequent chromosome variation de novo generated from euploid SHW-L1 plants at the 14th generation of selfing (F14). High frequent chromosome variations were also observed in the F2 hybrids and most of the analyzed recombinant inbred lines (RILs) at F14, derived from the cross of SHW-L1 with common wheat variety Chuanmai 32. Chromosome instability was associated with frequent univalency during meiotic metaphase I. The experiment on reciprocal crosses between SHW-L1 and Chuanmai 32 indicated that cytoplasm has not obvious effects on chromosome instability. An analysis on 48 F14 RILs revealed chromosome variation frequency was not associated with the Ph1 alleles from either SHW-L1 or Chuanmai 32, rejecting the hypothesis that chromosome instability was due to the Ph1 role of synthetic wheat. In the analyzed RILs, chromosome instability influences the phenotype uniformity, showing as obvious trait differences among plants within a RIL. However, the analyzed commercial varieties only containing ∼12.5% genomic components of synthetic wheat were chromosomally stable, indicating that chromosome instability caused by synthetic wheat can be effectively overcome by increasing the genetic background of common wheat.

Effect of different doses of group-2 chromosomes on homoeologous pairing in intergeneric wheat hybrids

1986 ◽  
Vol 28 (2) ◽  
pp. 240-246 ◽  
Author(s):  
C. Ceoloni ◽  
I. Strauss ◽  
M. Feldman
Keyword(s):  
Common Wheat ◽  
Chinese Spring ◽  
Intergeneric Hybrid ◽  
Homoeologous Pairing ◽  
Aegilops Variabilis ◽  
Group 2 ◽  
Wheat Hybrids ◽  
A Minor ◽  
Homoeologous Chromosomes ◽  
Different Doses

While an extra dose of chromosome 2A of common wheat, previously reported to carry a pairing promoter on its short arm, did not increase pairing between homoeologous chromosomes in F1 hybrids between common wheat cv. Chinese Spring (CS) and Aegilops variabilis, two doses of chromosome 2D or 2B caused a significant increase in homoeologous pairing. Evidently, chromosomes 2D and 2B carry a pairing promoter(s). Studies of F1 hybrids between aneuploids of CS, either deficient for chromosome 2D or having it in an extra dose, and Ae. variabilis, Ae. longissima, and Secale cereale supported the finding that this chromosome carries a pairing promoter. Using ditelosomic lines, the promoter was found to be located on the short arm of 2D (2DS). It was deduced that the promoter of 2B is also located on the homoeologous short arm, i.e., on 2BS. Evidence was obtained that the long arm of 2D may carry a suppressor(s) of pairing. Thus, the short arm of 2A, 2D, and 2B carries a pairing promoter(s), while the long arm of 2D and possibly of 2A and 2B carry a minor suppressor(s). The promoters are more potent than the suppressors and the overall effect of group-2 chromosomes is pairing promotion.Key words: wheat, homoeologous pairing, pairing promoter, pairing suppressor, intergeneric hybrid, meiosis.

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