Single Seed Descent Lines Research Articles

A comparison of anther culture derived material with single seed descent lines in Brussels sprouts (Brassica oleracea var. gemmifera)

Qualitative and quantitative studies show that diploid plants produced by anther culture (AC) from a double cross population of Brussels sprouts have arisen from spontaneously doubled haploid cells. The mean performance and distribution of lines produced by AC is compared to an equivalent array of inbred lines produced by single seed descent (SSD). There was no evidence of any difference in vigour between the AC and SSD samples. The tests are sufficiently sensitive to establish (with a 90 per cent confidence) that any true difference between the means, for vigour related traits, must be less than 15 per cent of the mean performance of SSD material. Additional evidence identifies genetic segregation for stability to micro-environmental factors within both the AC and SSD lines.

Field performance of lines derived from haploid and diploid tissues of Hordeum vulgare

Plant tissue culture technology is of increasing interest to plant breeders. As part of a continuing investigation into breeding methods with spring barley two studies were conducted to assess the field performance of the progenies of material regenerated in tissue culture. The first study involved two spring barley cultivars, 'Golden Promise' and 'Mazurka' and compared lines produced from immature embryo (IE) derived callus with those from embryos developed by the Hordeum bulbosum (Hb) technique of chromosome elimination. In general the mean values for the seven characters scored were lower for the IE than the Hb material. In the second study F1 hybrid material ('Golden Promise'x'Mazurka') was used and doubled haploid lines produced by the H. bulbosum and microspore culture (M) techniques were compared with single seed descent (SSD) material. Analysis of these F∝ samples indicated that the mean values for the M lines were significantly lower than those of the Hb and SSD lines. Furthermore, data from the M lines showed significant evidence of variation created during the culture phase. The implications of these findings for barley breeding are discussed.

The use of double haploids for detecting linkage and pleiotropy between quantitatively varying characters in spring barley

SUMMARYThe relationships between pairs of characters are investigated using F1 and F2 derived doubled haploids as well as single seed descent lines from spring barley (Hordeum vulgare) crosses. It is shown that linkage disequilibrium and pleiotropy are factors affecting the relationship between characters in barley. In fact, the linkages found are in general in the coupling phase and pleiotropy is usually positive. The consequences of such relations for plant breeding are discussed.

A comparison of androgenetic doubled-haploid, and single seed descent lines in Triticale

Sixty single seed descent (SSD) lines and about 25 anther-derived doubled-haploid (DH) lines were obtained from two triticale crosses. The frequency distributions of 10 quantitative agronomic traits were compared using parametric and non-parametric tests. A multivariate discriminant analysis was subsequently carried out. Gliadin patterns obtained from each line by polyacrylamide gel electrophoresis were used to calculate intra- and inter-population diversities from relative dissimilarity indices. It was found that DH and SSD lines show significant differences in frequency distributions of 1000 grain weight in both crosses, of heading date for one cross, and of lodging susceptibility for the other cross. The results of intra- and inter-population gliadin diversity indicate that although the SSD method theoretically provides more opportunity for recombination to occur than the DH method, it did not produce a greater range of recombinants. Since there is no significant difference between SSD- and DH-line distributions for grain yield, anther culture appears to be an efficient method for producing high yielding homozygous lines from F1 hybrids of triticale in a relatively short time.

The effect of linkage on additive genetic variance with inbreeding an F2

The effects of linkage on the additive genetical variation among inbred lines produced by single seed descent (SSD) from an F2 is investigated numerically with five and ten gene models. Although considerable bias can be generated by linkage, the additive genetical variation present after one round of random mating is shown to approximate closely to that among the SSD lines over a wide range of gene distributions and would thus be a reliable estimator for breeding purposes. Simple experimental methods of estimating this variance are discussed.

The effectiveness of early generation (F3) yield testing and the single seed descent procedures in two cowpea (Vigna unguiculata (L.) Walp.) crosses

Two breeding procedures were compared in two cowpea crosses. Both procedures were started from the same selected F2 plants in each cross. For the early generation yield testing, the F3 lines were yield tested and a pedigree and bulk methods followed in F4 and F5. Each F5 line was bulked to provide seed for a yield test in F6. In the Single Seed Descent (SSD) procedure, a single seed was taken from each F2 plant to produce the F3 generation. The procedure was repeated for the F4 and F5. The F6 SSD lines and the F6 yield testing lines were compared in yield tests. The results showed that differences in yielding ability of F3 lines persisted over generations indicating that selection was effective. This was confirmed by the high significant correlations between F3 yields and those of later generations which ranged from r=0.51* to 0.85**. The grain yields of lines derived by the single seed descent procedure were as good as those derived from early generation yield testing. Significant linear correlation between visual rating of F3 and F6 yields with actual yields revealed that it is possible to identify promising lines of cowpea visually.

Comparison of frequency distributions of doubled haploid and single seed descent lines in barley

Both doubled haploid (DH) and single seed descent (SSD) methods were used to derive homozygous lines from two crosses of barley. The frequency distributions of grain yield, heading date, and plant height of the DH and SSD lines were compared by the Mann-Whitney U test, Kolmogorov-Smirnov twosample test and Wald-Wolfowitz runs test. It was found that the DH lines distributed in the same manner as the SSD lines with respect to the three characters. The results indicated that although the SSD method had more opportunity for recombination than the DH method, it did not produce a sample of recombinants which differed significantly from the DH sample; thus both methods were equally efficient for use in deriving homozygous lines from F1 hybrids in a relatively short time.

Linkage and the Synthesis of Better Genotypes in Self‐fertilizing Species1

The basic task of the breeder of self‐fertilized species is the aggregation of superior alleles in a single pure line or cultivar. This study focused on the model problem of collecting into one line all the favorable alleles present in one or the other of any pair of pure lines. Background theory and simulation data are presented. The breeding procedure investigated involved intra‐line selection during the formation of single seed descent lines from an F2, followed by selection among the derived lines. We also considered recurrent use of the procedure; two selected lines from one cycle being crossed to provide the F2 base for the next cycle. Simulation was used to investigate the effect of genetic linkage on response to selection as reflected by probabilities of fixation of favorable alleles. As was to be expected, our data show that those probabilities are decreased by repulsion but increased by coupling linkages among the superior alleles. It follows that the impact of linkage depends on the way in which the superior alleles present in one parent line but not in the other are distributed among and within linkage groups. Assuming this to be random, our results indicate that, when parent lines are about equal in genetic value, the balance between repulsion and coupling will be such that linkage will have little effect on the average probability of fixation. However when one parent line is substantially better than the other, there will be more coupling linkage and the average probability of fixation will be increased. Nevertheless the average genetic value of selected lines will be less than or, at best, little above the level of the superior parent lineWe conclude that the full genetic potential of a two line gene pool is not likely to be achieved by the selection system described. Two systems believed superior to the one on which this study was focused are discussed. Both require increases in the proportion of seed produced by cross‐pollination but this may be justified by the associated potential for genetic improvement.

Breeding Progress in Tomato with Pedigree Selection and Single Seed Descent1

Abstract Estimation of breeding progress in 9 tomato populations subject to 4 generations of pedigree selection revealed significant generation differences for 5 of 12 variables measured. Cross effects were of greater magnitude than generation effects with response to pedigree selection measurable only for highly heritable characters. Mean value of lines derived from 2 or 3 generations of pedigree selection followed by single seed descent (SSD) to F6 or F7 were similar to their corresponding pedigree lines and approximately 50% of SSD lines derived following selection to F4 surpassed pedigree lines in weighted value. Early generation pedigree selection to F4 followed by selection among F6 SSD derived lines appears to be the most rapid and effective means of sampling variability in segregating populations.