C. N. Law

Genetic analysis of the dwarfing gene (Rht8) in wheat. Part I. Molecular mapping of Rht8 on the short arm of chromosome 2D of bread wheat (Triticum aestivum L.)

Abstractu2002Two sets of single chromosome recombinant lines comparing 2D chromosomes from the wheat varieties ‘Ciano 67’ and ‘Mara’ with the common 2D chromosome of ‘Cappelle-Desprez’ in a ‘Cappelle-Desprez’ background were used to detect a diagnostic wheat microsatellite marker for the dwarfing gene Rht8. The genetic linkage maps place the wheat microsatellite marker WMS 261 0.6 cM distal to Rht8 on the short arm of chromosome 2D. By PCR analysis the WMS 261 alleles of ‘Mara’, ‘Cappelle-Desprez’ and ‘Ciano 67’ could be distinguished by different fragment sizes of 192u2004bp, 174u2004bp and 165u2004bp, respectively. A screen of over 100 international varieties of wheat showed that the three allelic variants were all widespread. It also demonstrated that a limited number of varieties carried novel WMS 261 variants of over 200u2005bp. Following classification of the individual recombinant lines for allelic variants at the WMS 261 locus it was possible to attribute a 7- to 8-cm reduction in plant height with the WMS 261-192-bp allele compared to the WMS 261-174-bp allele in the set of recombinant lines comparing 2D chromosomes of ‘Mara’ and ‘Cappelle-Desprez’. A height reduction of around 3u2005cm was detected between the WMS 261-174-bp allele and the WMS 261-165-bp allele in the recombinant lines comparing 2D chromosomes of ‘Cappelle-Desprez’ and ‘Ciano 67’.

Genetic analysis of the dwarfing gene Rht8 in wheat. Part II. The distribution and adaptive significance of allelic variants at the Rht8 locus of wheat as revealed by microsatellite screening

Abstractu2002Wheat microsatellite WMS 261 whose 192-bp allele has been shown to be diagnostic for the commercially important dwarfing gene Rht8 was used to screen over 100 wheat varieties to determine the worldwide spread of Rht8. The results showed Rht8 to be widespread in southern European wheats and to be present in many central European wheats including the Russian varieties ‘Avrora’, ‘Bezostaya’ and ‘Kavkaz’. Rht8 appears to be of importance to South European wheats as alternative giberellic acid (GA)-insensitive dwarfing genes do not appear to be adapted to this environment. The very successful semi-dwarf varieties bred by CIMMYT, Mexico, for distribution worldwide have been thought to carry Rht8 combined with GA-insensitive dwarfing genes. Additional height reduction would have been obtained from pleiotropic effects of the photoperiod-response gene Ppd1 that is essential to the adaptability of varieties bred for growing under short-winter days in tropical and sub-tropical areas. The microsatellite analysis showed that CIMMYT wheats lack Rht8 and carry a WMS 261 allelic variant of 165u2004bp that has been associated with promoting height. This presumably has adaptive significance in partly counteracting the effects of other dwarfing genes and preventing the plants being too short. Most UK, German and French wheats carry an allelic variant at the WMS 261 locus with 174u2004bp. This could be selected because of linkage with the recessive photoperiod-sensitive ppd1 allele that is thought to offer adaptive significance northern European wheats.

Application of microsatellite markers to distinguish inter-varietal chromosome substitution lines of wheat (Triticum aestivum L.)

Wheat microsatellites (WMS) were used to test the authenticity of inter-varietal chromosome substitution lines developed using the varieties ‘Cappelle-Desprez’ and ‘Bezostaya 1’. The results demonstrated that the majority of the lines were correct. Microsatellites, with their abundance of polymorphic markers randomly distributed over the entire wheat genome, provided ideal tools for establishing the authenticity of cytogenetically developed genetic stocks of wheat.

Inter-varietal chromosome substitution lines in wheat - revisited

SummaryThe difficulties in developing inter-varietal chromosome substitution lines in wheat are reviewed. The use of genetical, cytological and molecular markers is suggested as a way of overcoming them. These difficulties and the use of markers, as well as the need to develop duplicate lines to detect background variation, are described using the development and analysis of the Cappelle-Desprez (Bezostaya 1) chromosome substitution set as an example. The effects of substituting Bezostaya 1 chromosomes on final plant height and adult-plant resistance to yellow rust are reported. The large number of aneuploids and substitution lines available in wheat provides a tremendous, international resource, which should be exploited in the future.

The influence of the group 1 chromosomes of wheat on ear-emergence times and their involvement with vernalization and day length

By using aneuploid lines of wheat in the variety Chinese Spring, each of the homoeologous group 1 chromosomes was found to delay ear emergence. More than one gene per chromosome was probably involved, and, because of the delays in ear emergence, at least one of them may be responsible for producing an inhibitor of flowering. The genes interacted with each other and with vernalization and day length. The genes on chromosome 1A were the most potent and 1B the least. The genes on the group 1 chromosomes may be related to the genes for vernalization and day-length sensitivity found on the homoeologous chromosome 1H of barley. Reciprocal monosomic analyses of three varieties detected allelic variation between homologues of group 1 for ear-emergence time.

Genetic manipulation in plant breeding — prospects and limitations

At the beginning of a meeting on genetic manipulation in plant breeding—it would seem appropriate that we should reflect upon the problems of feeding the predicted population expansion of the next century.

An assessment of the potential of 4DS.4DL-4s l L translocation lines as a means of eliminating tall off types in semi-dwarf wheat varieties

SummaryWheat varieties tend to be chromosomally unstable producing on average 2–3% of plants with abnormal chromosome numbers. A number of semi dwarf wheat varieties, carrying the gibberellic acid insensitive dwarfing genes Rht1 or Rht2, have been seen to produce distinct tall off types due to reduction in dosage of the chromosome carrying the dwarfing gene. The UK variety ‘Brigand’, carrying Rht2 on chromosome 4D, produced very distinct tall off types when this chromosome was reduced in dosage. The frequency of tall off types was sufficiently high to cause the variety to fail United Kingdom statutory uniformity tests. An attempt to prevent the loss of chromosome 4D was made by constructing translocation chromosomes involving the short arm of chromosome 4D, which carries Rht2, and the long arm of chromosome 4Sl from Aegilops sharonensis, which carries a gene(s) conferring preferential transmission. The work in this paper describes the field evaluation of two lines carrying 4DS.4DL-4Sl L translocations, and demonstrates their success in preventing spontaneously occurring monosomy of chromosome 4D in semi-dwarf wheats.

Exploitation of chromosome 4S 1 , from Aegilops sharonensis , for the production of stable 44-chromosome wheat lines

A number of chromosomes from species related to wheat carry genes of potentially high agronomic value. However, wheat lines carrying an additional pair of such chromosomes have never been exploited commercially because they are unstable and the extra chromosomes are frequently lost during gametogenesis. In order to overcome this problem translocations involving the long arm of the Aegilops sharonensis chromosome 4S1, which carries the gene(s) determining preferential transmission, and the long and short arms of chromosome 1U from Aegilops umbellulata, which carry respectively the genes Glu-U1 and Gli-U1, which affect bread making quality, have been isolated. These translocations are stable and preferentially transmitted.