A comparison of the levels of hydroxamic acids in Aegilops speltoides and a hexaploid wheat and effects on Rhopalosiphum padi behaviour and fecundity.

Hydroxamic acids (HAs) are plant secondary metabolites produced by certain cereals, which have been found to be toxic to pest aphids in artificial diet assays. Previous studies have shown that tetraploid and hexaploid wheat varieties, the leaf tissues of which contained higher levels of these compounds than used in artificial diets, did not reduce aphid settling or fecundity. This current study reports findings on a high HA producing B genome accession of the diploid ancestor of wheat, Aegilops speltoides. We found that this accession does have a negative impact on aphid host selection and substantially reduces nymph production. Whole leaf tissue assays showed very high levels of HAs, well in excess of the toxic level determined in the artificial diet assays. Extraction of the apoplast fluid (AF) from this accession showed that the HA level is much lower than that of the whole tissue, but is still close to the artificial diet toxic level. Furthermore the HA level in the AF increases in response to aphid feeding. These observations could explain why hexaploid wheat remains susceptible to aphids, despite having whole leaf tissue HA levels in excess of the toxic levels determined in artificial diets.

Short, natural, and extended photoperiod response in BC2F4 lines of bread wheat with different photoperiod-1 (Ppd-1) alleles.

Flowering is a critical period in the life cycle of flowering plant species, resulting in an irreversible commitment of significant resources. Wheat is photoperiod sensitive, flowering only when daylength surpasses a critical length; however, photoperiod insensitivity (PI) has been selected by plant breeders for >40 years to enhance yield in certain environments. Control of flowering time has been greatly facilitated by the development of molecular markers for the Photoperiod-1 (Ppd-1) homeoloci, on the group 2 chromosomes. In the current study, an allelic series of BC2F4 lines in the winter wheat cultivars 'Robigus' and 'Alchemy' was developed to elucidate the influence on flowering of eight gene variants from the B- and D-genomes of bread wheat and the A-genome of durum wheat. Allele effects were tested in short, natural, and extended photoperiods in the field and controlled environments. Across genetic background and treatment, the D-genome PI allele, Ppd-D1a, had a more potent effect on reducing flowering time than Ppd-B1a. However, there was significant donor allele effect for both Ppd-D1a and Ppd-B1a, suggesting the presence of linked modifier genes and/or additional sources of latent sensitivity. Development of Ppd-A1a BC2F4 lines derived from synthetic hexaploid wheat provided an opportunity to compare directly the flowering time effect of the A-genome allele from durum with the B- and D-genome variants from bread wheat for the first time. Analyses indicated that the reducing effect of Ppd-A1a is comparable with that of Ppd-D1a, confirming it as a useful alternative source of PI.

QTL analysis of an intervarietal set of substitution lines in Brassica napus: (i) Seed oil content and fatty acid composition.

Backcross breeding with marker-assisted selection was used to construct an intervarietal set of part chromosome substitution lines in Brassica napus, formed from a cross between two winter varieties of oilseed rape: Tapidor and Victor. A total of 22 lines from this substitution library were examined over a 3-year period, in a total of nine field trials, for seed oil fatty acid composition and seed oil content. Trialing of the substitution lines gave evidence for the existence of 13 quantitative trait loci (QTL). All 13 QTL affected fatty acid composition of the seed, and were distributed among linkage groups 1, 3, 6, 7, 8, 11, 13, 14, 18, and 19. Seven of these QTL, on linkage groups 3, 6, 8, 13, 14, 18, and 19, also affected total seed oil content. The positions of these QTL are compared to those in the published literature and with respect to erucic acid QTL previously identified in a backcross population of the same cross. The substitution line approach gives increased precision and sensitivity for QTL mapping compared to other methods.

Prediction of the performance of inbred lines derived from a population cross in autumn-sown onions (Allium cepa L.).

A design and model are presented to allow the prediction, in early generations, of the mean and distribution of recombinant inbred lines derived from a cross between two parental populations or partially inbred lines. The procedure has been tested in autumn-sown onions (in the UK) using a wide cross between the openpollinated Japanese cultivar, Senshyu, and a partially inbred line derived from the European cultivar, Rawska. The early generations used for prediction included the first self-pollinated generation of the two parental populations and the F3 generation produced from the hybrid population. The predictions were tested by reference to the field performance of a random array of inbred lines, which were produced by single-seed descent (SSD) and had been selfed for three generations. The early generations, used for prediction, and a sample of SSD lines were raised alongside each other in each of two seasons. Within each season, good agreement was found between the predicted and observed performance of the recombinant inbred lines for three characters - yield, quality and maturity. This is used as evidence of the validity of the genetical model and the assumptions made. The effects of genotype x environment interactions prevented predictions made in one season being reliably applied to those made in the other and, therefore, reduce the attraction of this type of prediction study to the plant breeder.

Performance of recombinant inbred lines in Brussels sprouts (Brassica oleracea var. gemmifera).

Performance of a random array of recombinant inbred lines derived by single seed descent from five different source populations of Brussels sprouts (Brassica oleracea var. gemmifera) is presented. A total of 2,356 lines were tested in trials during 1985 and 1986. Three of the source populations were derived from double crosses between F1 hybrids. These hybrids show a considerable heterotic advantage over their inbred parents for the most important agronomic traits. The recombinant inbred lines performed, on average, less well than the parental inbred material, indicating that additive x additive genie interactions may make a significant contribution to the performance of current inbred material. Nevertheless, the very large variation among the recombinant inbred lines permitted many lines to be identified which outperformed the best parental inbred for all traits. Two lines outperformed the reference F1 hybrid, Gower, for an index that included marketable yield and quality. Consideration was also given to the dangers of misinterpreting phenotypically based proportions. Accordingly, response equations were used to ascertain the real genetic progress that was made. Advance seemed small when compared with the large heterotic effect, which is consistent with the segregation of a large number of loci. The distribution of the recombinant inbred lines was compared to predictions made from early generation trials. There was broad agreement but significant discrepancies existed which, it is suggested, may arise from the effects of genotype-environment interactions.