The success of a plant breeding program depends upon the availability of useable genetic diversity. Such diversity may be enhanced depending on the type of hybridization strategy employed. Segregating progenies resulting from F2 populations, a double cross, and a top cross were compared for the amount of useable genetic diversity associated with six traits in durum wheat. The parental lines were three winter selections, H7092-11, H7092-52, and WD5, and two spring cultivars, WPB 881 and Altar 84. Traits evaluated were (1) plant height, (2) days to maturity, (3) harvest index, (4) kernel weight, (5) grain yield, and (6) pigment content. Analysis of the population mean values suggested the superiority of the F1 top cross for plant height, kernel weight, and grain yield. The F1 top cross progeny also had the highest genetic variability for grain yield. F2 population of the cross Altar 84 I H7092-52 gave the highest mean values for days to maturity and harvest index, and showed the highest genetic diversity for traits other than grain yield. The only population showing detectable genetic variance for pigment content was the F2 progeny of the single cross WPB 881 / H7092-11. When genetic diversity was detected, the double cross was approximately intermediate between the two F2 populations from which it was derived. Transgressive segregation was more frequent in the top cross population for grain yield, kernel weight, and plant height. No associations between grain yield and the other traits were noted for the F2 population of the single cross Altar 84 I H7092-52 and the top cross population. For the second F2 population (WPB 881 / H7092-11) and the double cross population, grain yield was found to be associated with harvest index and plant height. The only consistent relationship across all segregating generations was a negative correlation between plant height and harvest index. Based on the genetic diversity and the transgressive segregation observed, top crossing appears to be the more promising in improving grain yield in the experimental material investigated. For specific traits other than grain yield, it would appear that single crosses would be a more productive approach, however progress would depend on the specific parental combination. The double cross was inferior to the other crossing strategies for the traits measured. / Graduation date: 1991

1 v. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Agronomy, Waite Agricultural Institute, 1986

Typescript, etc.

Competition with weeds decreases crop yields globally. Some traits are known to confer a competitive advantage to spring bread wheat (Triticum aestivum L.), but complex relationships between the competitive traits makes breeding for competitive ability difficult. Prairie organic producers use spring wheat cultivars which have been bred for conventional management systems or heritage cultivars released before the widespread use of synthetic fertilizers and pesticides. Breeding spring wheat specifically for organic production has been suggested. The International Triticeae Mapping Initiative (ITMI) population was used to study the genetics of traits associated with competitive ability. Grain yield without weed competition and under experimentally sown cultivated oat competition exhibited similar heritability. Similar heritability estimates between competition treatments suggest that selection in a weed free environment can lead to improvements in a weedy environment, but some high yielding lines under competition would be eliminated during selection. Quantitative trait loci (QTL) analysis of the population found QTL associated with vigour, days to heading, anthesis, and maturity, and cultivated oat grain yield suppression on chromosome 5A. The genetic correlations support the idea that early maturity provides a competitive advantage in northern grain growing regions. To investigate the feasibility of organic wheat breeding we used a random population of 79 F6-derived recombinant inbred sister lines from a cross between the Canadian hard red spring wheat cultivar AC Barrie and the CIMMYT derived cultivar Attila. The population, including the parents, was grown on conventionally and organically managed land in 12 environments over three years. Six environments had detailed agronomic data and heritability estimates differed between systems for five of the 14 traits recorded. Direct selection in each management system (10% selection intensity) resulted in 50% or fewer lines selected in common for four of the traits. Over all 12 environments direct selection within management system resulted in three lines retained specific to each system. The results of the management studies suggest that selection differences occur across multi-location tests, and selection for grain yield in organic systems should be conducted within organic systems. However, data garnered from conventional yield trials does have some relevance towards breeding for organic environments. / Plant Science

No description available.

159 leaves : tables, graphs, photos ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1977) from the Dept. of Agronomy, University of Adelaide

Photocopy of typescript / v, 177 leaves, 6 leaves of plates : ill. (part col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.) Dept. of Agronomy, University of Adelaide, 1981

Please read the abstract in Chapter 6 of this document / Dissertation (MSc (Genetics))--University of Pretoria, 2000. / Genetics / unrestricted

"March, 2004" / Bibliography: leaves 204-229. / xv, 229 leaves : ill. (some col.), map (col.), photos (col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The outcome of the yield evaluation trials conducted in this study was the identification of the high-yielding and widely adapted line, RH912025, which was consequently released as the variety Tamaroi. Development of B tolerant lines, with a grain yield advantage when grown under high B conditions in the field, means durum production will be able to expand into the marginal areas where B toxicity occurs. Furthermore, by pyramiding genes for B tolerance and dough strength (i.e. subunit 2*) into Tamaroi, the result should be widely grown germplasm, with premium quality for the international market. --p. x. / Thesis (Ph.D.)--University of Adelaide, School of Agriculture and Wine, Discipline of Plant and Pest Science, 2005

Pre-harvest sprouting in wheat costs farmers millions of dollars every year. Pre-harvest sprouting tolerance (PST) has minimized this problem, but improvement of PST is still necessary. Synthetic hexaploid wheats (synthetics) have been used as sources of genes coding for many useful traits. Two studies evaluated the PST of a synthetic (Altar 84/Aegilops tauschii) and investigated its potential as a source of PST in crosses with wheat cultivars. The first study compared the synthetic with selected wheat checks for PST and with its parent Altar 84 for the germination response of these genotypes to controlled wetting treatments applied to field-grown intact spikes and threshed seed. Spikes were rolled in wet germination paper and the percentages of germinated seed were determined after seven days. Threshed seeds in Petri dishes were wetted with water and vegetative floral tissues (chaff) extracts. Germinating seeds were counted daily for 14 days. The synthetic was more tolerant than Altar 84 and was classified as moderately sensitive. The improved PST of the synthetic over Altar 84 was attributed to Aegilops tauschii. Seed dormancy and water-soluble substances in the chaff of the synthetic and other genotypes appeared to contribute to their PST. The second study used random inbred F��� lines obtained from single and backcrosses between the synthetic (red-seeded) and the sensitive wheat cultivars Opata F��� (red-seeded) and Bacanora 88 (white-seeded). Seed coat color and germination responses of the F5 lines subjected to a five-day spike wetting treatment were evaluated. Pre-harvest sprouting tolerance was moderately to highly inheritable and largely controlled by additive gene effects in the studied populations. An association between red seed coat color and PST was observed but white recombinant lines more tolerant than their sensitive parent were obtained. The synthetic can be used to improve wheats with red and white seed coats. The potential use of the synthetic as a PST source was discussed and a breeding strategy suggested. / Graduation date: 1999