Estimation of outcrossing rate in landraces of tetraploid wheat (Triticum turgidum L.)

A study was undertaken to assess the amount of natural outbreeding in tetraploid wheat landraces of Ethiopian origin. The study consisted of two trials which were planted separately at two locations representing different environmental conditions for two consecutive seasons. The design employed was the randomized complete block with three replications. Two polymorphic loci, glume pubescence and awn condition were utilized as markers. The rate of outcrossing was based on the number of hybrids found in the recessive class of each marker. The overall level of outcrossing was higher in the pure stand trial than in the mixed stand trial. A higher rate of outcrossing occurred in the higher altitude area in the pure stand trial while the opposite was the case in the mixed stand trial. The average rate of outcrossing due to the marker loci was also different, with the long awn displaying more outbreeding tendency. Both locational and seasonal differences in the amount of outcrossing were observed. Generally, the study has revealed that there is a considerable amount of outbreeding in the landraces and that this genetic factor could play a role in preserving variation in the landrace populations. The level of outcrossing detected in this study could have a bearing on the maintenance of the genetic purity of diverse breeding lines being handled together in a breeding nursery and varietal purity in seed multiplication.     

Response to selection in F2 generations of winter wheat for resistance to head blight caused by Fusarium culmorum

Summary In a field trial, F₃ winter wheat lines from plants selected for Fusarium head blight resistance in F₂ generations of a set of crosses, composing a 10×10 half diallel, were tested with their parental lines for resistance to Fusarium culmorum. Selection responses averaged 3.7% on the head blight percentage scale and ranged from –22.0% to 27.1%. Realized heritabilities averaged 0.23 and ranged from 0 to 0.96. Significant transgression for resistance was observed which was suggested to be genetically fixed. It was estimated that resistant parents differed in one or two resistance genes. The possibility of accumulation of resistance genes was shown. The level of head blight resistance of the parental line appeared to be a good indicator of the potential resistance level of its crosses.     

Abortion of infection structures of wheat leaf rust in susceptible and partially resistant wheat genotypes

Summary Arrest of the growth of wheat leaf rust infection structures was studied with fluorescence microscopy in seedling leaves and flag leaves of the susceptible spring wheat genotypes Morocco and Kaspar and the partially resistant genotypes Westphal 12A and Akabozu. The percentages non-penetrants and substomatal vesicle abortion were low in all genotypes. In the partially resistant genotypes the percentage abortion of infection structures was higher than in the susceptible genotype Morocco. Aborted infection structures had formed one or two haustorial mother cells. In adult plants differences in the percentage aborted infection structures between susceptible and partially resistant genotypes were more pronounced than in seedlings. The so-called late abortion was not observed.     

Further Studies on the Restoration of Fertility in Triticum durum×T. timopheevi Hybrids

Twenty one F₁ hybrids involving three Triticum durum cultivars and eleven forms of T. timopheevi were backcrossed to their respective durum parents. Backcross fertility (BC₁ grain set) of these sterile hybrids improved with the rise in temperature at the time of pollination. A mean temperature of less than 20 °C results in poor seed set while higher mean temperatures around 24 °C result in increased seed set. It is suggested that a large number of backcross seeds can be produced by pollinating these hybrids late in the season, i.e., after 20th of March in northern India.     

The presence of three groups of Scalavatis and other hexaploid bread wheat plants contaminating durum wheat fields in Cyprus

Summary The mutual resemblance of 81 hexaploid wheat plants contaminating durum fields on Cyprus was investigated by determining their phenotypes of gliadins, glutenins and peroxidase. Three groups were generated by clustering programs. Group 1 consists of plants with ears resembling those of durum plants, plants of groups 2 and 3 have a bread wheat appearance. Suggestions on the origin of these three groups are made. Group 1 may derive from (back)crosses between hexaploid and durum plants since time immemorial. If so, the hexaploid plants would have served as donor of the D genomes, and durum plants as the recurrent parent. Groups 2 and 3 may derive from two introductions, either from two countries, or from the same country, but then in different periods.     

The inheritance of host plant effect on latency period of wheat leaf rust in spring wheat. I: Estimation of gene action and number of effective factors in F1, F2 and backcross generations

Summary Crosses were made between the highly susceptible Little Club and the partially resistant cultivars Westphal 12A, Akabozu and BH 1146 to obtain F1, F2 and backcross generations. Latency period (LP) was determined in plants inoculated at the young flag leaf stage with a monospore culture of race Flamingo of wheat leaf rust. Broad sense heritability of LP in the F2 averaged 0.8. The genes showed partial to almost complete recessive inheritance. Scaling tests indicated that additive gene action was the most important factor in the inheritance of partial resistance. The tests showed that there were no indications for additive x additive, additive x dominance or dominance x dominance interactions. The number of effective factors was estimated as one or two for Akabozu, three or more for Westphal 12A, and two or three for BH 1146. BH 1146 also possessed a (semi-)dominant gene for a lower infection type which was temperature sensitive in its expression. The genes of the various parents had unequal effect on LP.     

The effect of transfers of alien genes for leaf rust resistance on the agronomic and quality characteristics of wheat

Summary Nine transfers of leaf rust (Puccinia recondita Rob. ex Desm.) resistance to wheat (Triticum aestivum L.) from Agropyron elongatum Host. Beauv., Triticum speltoides Tausch and rye (Secale cereale L.) were backcrossed up to 10 times to commercial wheat cultivars. The objective was to study the effect of the transfers on agronomic and quality characters and to make them available in desirable genetic backgrounds. The results varied greatly for different transfers. In four cases no promising material was obtained even after nine backcrosses. However, for the remaining five transfers material with potential as a new cultivar was obtained.     

The relationships of hardening period and the expression of frost resistance in chromosome substitution lines of wheat

Summary The highly frost resistant wheat variety Cheyenne (donor) and the poorly frost resistant variety Chinese Spring (recipient) were frozen at –9° C and –11° C at various stages of hardening, as were a number of substitution lines of these two varieties (CS/Ch 3A, CS/Ch 5A, CS/Ch 7A, CS/Ch 2B, CS/Ch 4B, CS/Ch 5B, CS/Ch 4D, CS/Ch 5D). Chromosomes 5A, 5B, 5D, 4B and 7A of Cheyenne increased the frost resistance of the recipient variety to varying extents. However, the frost resistance changed not only as a function of the different chromosomes, but also as a function of the duration of hardening, indicating that genes responsible for frost resistance are expressed differently during different phases of the hardening process.     

Diallel analysis of resistance to Septoria tritici isolates in durum wheat

Summary All crosses, except for reciprocals, were made among ten cultivars originating from crop improvement programs in North Africa and the Middle East. The entries varied widely in reaction to Septoria tritici. F₁ and F₂ progenies of the crosses were evaluated using eight S. tritici isolates from seven countries in the Mediterranean area. Thus, sixteen separate combining ability analyses were excecuted. General combining ability (GCA) was the major component of variation, although specific combining ability (SCA) was present in most cases. Additive variance thus appears to be of predominant importance. Nevertheless, non-additive variance may interfere when line selection in a breeding program is practiced. While differing greatly among cultivars, specific GCA effects for each cultivar separately were of similar magnitude for all isolates. Ranking statistics determined that cultivars were ranked in similar order for both means and specific GCA effects independent of the isolate used. Different isolates may therefore interact with similar or identical genetically controlled mechanisms in a particular cultivar. This could indicate the absence of differential gene-for-gene relationships and suggests that isolates vary in aggressiveness rather than in virulence.     

Chromosome constitution in G2 and G3 progenies of 6x-triticale × T. turgidum L. hybrids

Summary Rye chromosome constitution and stability in a series of plants of G2 and G3 generations obtained after the cross between hexaploid triticale and durum wheat (F1: 2n=5x=35; genomes AA BB R) are studied using the zymogram phenotype expression for the following isozyme marker genes: Mdh-2c1 (1R), Cpx-c2 (2R), Got-3-c1 (3R), Pgm-c1 (4R), Est-c6 (6R), Got-2-c1 (6R), Acph-c1 (7R) and Got-1-c1 (7R). The results were corroborated using C-banding in a sample of the plant population studied and make clear the utility of biochemical methods in quick cytogenetic analysis. From the results, a different rate of transmission for each rye chromosome is inferred.