Detection of repeated genotypes among 93 diploid wheat accessions

Summary An objective procedure was developed to find and eliminate repeated genotypes from a set of crop cultivars or accessions which may be used as parents for future plant breeding programs. Nonhierarchical, nonexclusive, exhaustive cluster analysis was used to group 93 diploid wheat accessions using LSD multiple comparisons of accession means based on data measured on seven characters. Beginning with the rarest accessions, i.e. those represented in the fewest clusters resulting from the clusters analysis, a minimum number of the accessions were chosen to represent the phenotypes of all 93 of the accessions. Two analyses were performed, one using data from an irrigated trial, the other from a dryland trial. The dryland trial data was more discriminating in that it required 71 accessions to represent all of the clusters generated from the original 93 accessions while the irrigated trial data required only 60 of the 93 accessions. In addition to the 71 accessions chosen from the dryland trial analysis, the irrigated trial analysis suggested an additional 12 accessions were phenotypically and, therefore, genotypically unique. The total of 83 unique accessions left 10 phenotypically duplicate accessions to be eliminated from the set of potential parents. Four of the 10 duplicated accessions were rare in that they were represented in very few clusters in either the irrigated trial analysis or in the dryland trial analysis. Because their phenotypes were not unique in spite of being rare, we believe such accessions were duplicated genotypically as well as phenotypically. The other six duplicates were common in that they were represented in a large number of clusters. Such accessions may not prove to be duplicates if grown in additional environments (trials), or if measured on additional characters.     

The Influence of Plant Developmental Stage on Expression of Resistance to leaf Rust (Puccinia recondita) in Two Near Isogenic Lines of Wheat

Cultivar ‘Thatcher’, and ‘Thatcher’ lines with Lr 21 and Lr 22 were studied against a number of races of Puccinia recondita for seedling and adult plant reaction. The study has established that Lr 21 and Lr 22 are genes effective against P. recondita at adult plant stage. It has also shown that these genes confer resistance against all races when plants are inoculated at boot leaf stage.     

Honeycomb selection for yield in early generations of spring wheat

Summary The effectiveness of the honeycomb selection method for yield in spring wheat (Triticum aestivum L.) was evaluated using progenies from two wheat crosses, Glenlea x NB131 and Glenlea x Era. Honeycomb selection was carried out in the F₂ and F₃ generations, grown at the University of Manitoba in the summers of 1980 and 1981, respectively. In both generations, divergent selection was made for both high and low yield. Plants selected in the F₃ generation were entered in an F₄ yield test in the summer of 1982. Results of the experiment showed that honeycomb selection for yield in the F₂ and F₃ generations was effective in identifying parents of high- and low-yielding lines. F₃ plants from highyielding F₂ selections gave higher yields than those from low-yielding F₂ selections by 11.5% and 13.0% for Glenlea x NB131 and Glenlea x Era crosses, respectively. The F₄ yield test showed that high yielding selections from both crosses significantly outyielded by 8.9% low yielding selections and by 14.4% the unselected composite lines. It is concluded that the honeycomb selection method can be used for early generation selection in spring wheat.     

A Possible Association Between Heading Time and the GM-A2 Locus in Bread Wheat

A line without expression (null form) o: the α-gliadins controlled by the 6A chromosome was found when screening electrosboretically single seeds of the bread wheat ‘Raeder’. Differences in heading time were also observed between this null line and the normal one. A linkage between 6A gliadin genes and heading time gene(s) is hypothesized.     

The degree of phenotypic resemblance of the near-isogenic lines of the wheat cultivar thatcher with their recurrent parent

Summary Thatcher, 16 of its near-isogenic lines (NIL) and 8 donors were investigated for the degree in which the NILs phenotypically resembled their recurrent parent. In general the NILs have a good phenotypic resemblance. In a few NILs characters occur that are not seen in Thatcher. In some cases these are found in the donor indicating the presence of donor genes other than the marker gene in the NIL. In other cases a character possessed by a NIL is not present in Thatcher or in its donor. In such cases either inhibitor genes may play a part, or the donor accession that accompanies the set of NILs may not be the donor used to breed the NIL. Two causes are possible. One is that the donor was a mixture of genotypes, the other is contamination.The presence of donor genes other than the marker Lr gene(s) in a NIL may lead to unexpected results or, what is worse, to wrong conclusions.     

Additive gene action for resistance to Puccinia striiformis F.SP. Tritici in Triticum dicoccoides

Summary Seven single-plant selections of wild emmer, with temperature-sensitive minor-effect genes for stripe rust resistance, were intercrossed in eight combinations. The resulting progenies were studied for a possible additive gene action.The transgressive segregation towards resistance in F₂ observed in all the combinations indicates that additive gene action for resistance indeed occurs in wild emmer. The common occurrence of this phenomenon in random combinations suggests further that several minor-effect genes are involved.Following selection of the most resistant plants in F₂, a marked shift towards resistance was noted in F₃, which demonstrates a positive response to selection. In some instances, additive resistance selected for (in F₂) at the high temperature-profile was expressed (in F₃) also at the low temperature-profile. This kind of resistance, when utilized in breeding programmes, promises therefore to be effective over a range of temperatures.     

Influence of high molecular weight glutenin subunit substitution on rheological behaviour and bread-baking quality of near-isogenic lines developed from Chinese wheats

Three near‐isogenic lines (NILs) of wheat involving Glu‐B1 and Glu‐D1 alleles were used to study the genetic contribution of high molecular weight glutenin subunits (HMW‐GS) to gluten strength. The HMW‐GS composition of each NILs was determined by SDS‐PAGE. No significant differences were found in grain protein contents among the NILs. Gluten strength and dough‐mixing properties were measured by the Farinograph, the Extensograph, and SDS‐sedimentation (SDS‐SE). Results indicated that line 2, containing the Glu‐1B 14 + 15 and Glu‐1D 5 + 10 combination of subunits, had higher values for flour quality, dough rheological parameters, and bread‐baking quality when compared with lines 8 and 13. Line 8, containing Glu‐1B 7 + 9 and Glu‐1D 5 + 10, was better than line 13 with the Glu‐1B 14 + 15 and Glu‐1D 10 combination. Some major parameters appeared significantly different. The presence of Glu‐1B 14 + 15 was associated with higher dough strength based on SDS‐SE volume and several rheological parameters when compared with Glu‐1B 7 + 9. Lines with subunit 10 at Glu‐D1 performed significantly worse than those with 5 + 10 in gluten index, SDS‐SE volume, Farinograph stability time, Extensograph area and bread‐baking quality.     

Selection for resistance to Septoria nodorum in wheat

Summary A population of 572 F₂ derived F₃ lines from six crosses were used to estimate parameters relevant to selection for resistance to Septoria nodorum of wheat. Lines were grown in disease free (fungicide sprayed) and inoculated microplots in 2 replications of a split-plot design in a single environment in 1977. Average yield reduction due to disease was approximately 50%; this was associated with an average septoria score of 50% on the flag leaf, an average septoria score of 42% on the head, and a reduction of 37% in seed weight. Low S. nodorum scores were correlated with late heading date, tall plant height, high grain yield, and high seed weight in diseased plots, and high seed weight % (seed weight in diseased plots expressed as a percentage of seed weight in fungicide sprayed plots).Restricted selection indexes were used to study the relative contributions of disease escape, true resistance, and tolerance to variability in grain yield in diseased plots, seed weight in diseased plots, and seed weight %. True resistance appeared to be the most important factor causing variation in grain yield in diseased plots and seed weight %. Tolerance and escape seemed to be more important for seed weight in diseased plots.Heritabilities of S. nodorum scores on the flag leaf and head were 63% and 52%, respectively. Leaf and head scores could be used most effectively as selection criteria to upgrade resistance in a population before harvest.Selection for high seed weight % slightly reduced yields in disease free plots, although yield in diseased plots and seed weight in diseased plots were increased. However, selection for increased yield or increased seed weight in diseased plots improved yield in disease free plots. It is suggested that direct selection for yield or seed weight in diseased plots is likely to achieve more desirable goals than selection for seed weight %.     

Inheritance and chromosomal location of the homoeologous genes affecting phenol colour reaction of kernels in durum wheat

End-use quality of wheat for noodles is influenced by polyphenol oxidase activity and its corresponding substrates. This study investigated the chromosomal location of genes that determine phenol colour reaction of kernels in tetraploid wheat using aneuploid stocks. Polyphenol oxidase activity was estimated by the colour reaction of kernels to phenol solution. It was found that the genes located on homoeologous group 2 chromosomes have an important effect on the level of phenol colour reaction of kernels. The genes (Tc1 and Tc2) responsible for high phenol colour reaction of kernels were mapped to the long arms of chromosome 2A and chromosome 2B, respectively. The map distances were estimated to be 46.8 cM for Tc1 and 40.7 cM for Tc2 from the centromere using double-diltelosomics of durum wheat.     

AFLP analysis indicates no introgression of maize DNA in wheat x maize crosses

Amplified fragment length polymorphisms (AFLPs) were used to follow the possible introgression of maize DNA into haploids of wheat as a side‐effect of exploiting wheat x maize hybridization for haploid production. AFLPs were generated with 64 MseI/ EcoRI and 64 MseI/ PstI primer combinations, and the AFLP profiles of haploids were tested against those of maize and of the regular wheat varieties involved in the crosses. On average, 45.1 and 110.7 fragments were produced per assay with the MseI/EcoRI and MseI/PstI combinations, respectively. Different numbers of fragments were produced for wheat and maize: an average of 81 in the haploid, 80 in the wheat parent, and only 67.1 in maize. No evidence was found for introgression of maize into the wheat genome. Three unique AFLP fragments were detected in haploids, which were not present in the parental wheat genotypes. These ‘novel’ AFLP bands in the haploids could be caused by nucleo‐cytoplasmic interaction in the hybrid zygote. Such instability in the wheat genome is defined as temporal, as it was not detected in further generations when colchicine‐doubled progeny of the haploids was tested for the presence of polymorphic fragments.