| Materials and Methods The single chromosome substitution lines of the group 5 homoeologous chromosomes of the varieties Hope and Cappelle Desprez into Chinese Spring were produced by Professor E. R. Sears, University of Missouri, Columbia, Missouri, U.S.A. and by Dr. C. N. Law and Mr. A. J. Worland, Plant Breeding Institute, Cambridge, England, respectively. SNAPE et al. (1979) demonstrated that these two donor varieties are non-crossable with tetraploid H. bulbosum. All H. bulbosum pollinations were made using the tetraploid H. bulbosum clone PB168, originally obtained from Dr. D. B. H. Sparrow, from the Turkey collection CPI 18968, entry number 73/3. The chromosome 5D substitution lines were vernalized for two weeks, at 4C with an 8-hour daylength, to promote flowering because both donor varieties possess winter alleles at the Vrn3 locus on chromosome 5D controlling vernalization requirement (LAW et al. 1976). The H. bulbosum clones were vernalized under identical conditions for 8 weeks to promote flowering, and grown, together with the wheat genotypes, in an unheated glasshouse during the summer. All crossing procedures were carried out as described by SITCH et al. (1985) on 12 spikes per genotype. The percent seed set was established for each spike individually and then averaged over contributing spikes. The statistical analysis was carried out using data transformed to angles. Results The table of means of Chinese Spring and the six substitution lines and the analysis of variance for seed setting ability are shown in Tables 1 and 2 respectively. The seven genotypes differed significantly in seed setting ability. The seed set obtained on the 5A and the 5B chromosome substitution lines of Hope and Cappelle-Desprez was significantly lower than that obtained on Chinese Spring. The crossability of the 5D substitution lines, however, was not significantly different from Chinese Spring. This implies either that Hope and Capelle-Desprez possess an allelle of small effect at the third crossability locus, Kr3, on chromosome 5D or that, in these varieties, this locus is represented by an allele equivalent to that of Chinese Spring. The variation in crossability of the six substitution lines was partitioned into the main effects of the three chromosomes, of the two varieties and the interaction between these two main effects, Table 2. The overall crossability of chromosomes 5A, 5B and 5D differed significantly, the 5D chromosome substitution lines having the highest crossability and the 5B chromosome substitution lines the lowest. The variation between chromosomes was further partitioned to allow a comparison between chromosome 5B and the remaining chromosomes, and between chromosomes 5A and 5D. This indicated that a large proportion of the variation in the overall crossability was attributable to the severe reduction in percent seed set caused by Kr1 on chromosome 5B. However, the allele Kr2, on chromosome 5A, also contributed towards this variation since the overall crossability of the 5A substitution lines was significantly lower than that of the 5D substitution lines. An overall comparison of the crossability of the substitution lines derived from Hope and from Cappelle-Desprez showed that the mean of the group 5 chromosome substitutions did not differ significantly. However, the significance of the interaction implies allelic variation between the homoeologous chromosomes of Hope and Cappelle-Desprez. A partitioning of this variation into a comparison between chromosome 5B and the remaining chromosomes, and between chromosomes 5A and 5D, revealed that the allelic variation between Hope and Cappelle-Desprez was attributable to allelic differences at both the Kr1 and Kr2 loci. The Kr1 allele on chromosome 5B of Hope was significantly (p < 0.05) more potent than that of Cappelle-Desprez in suppressing crossability. In contrast, the Kr2 allele from Hope was significantly (p < 0.05) less effective than that from Cappelle-Desprez. |
| <-- Back | | | --> Next |