Genetic variation for carbon isotope discrimination in sunflower: Association with transpiration efficiency and evidence for cytoplasmic inheritance

Plants accumulate isotopes of carbon at different rates because of discrimination against C-13 relative to C-12. In plants that fix carbon by the C-3 pathway, the amount of discrimination correlates negatively with transpiration efficiency (TE) where TE is the amount of dry matter accumulated per unit water transpired. Therefore, carbon isotope discrimination (Delta) has become a useful tool for selecting genotypes with improved TE and performance in dry environments. Surveys of 161 sunflower (Helianthus spp.) genotypes of diverse origin revealed a large and unprecedented range of genetic variation for Delta (19.5-23.8parts per thousand). A strong negative genetic correlation (r(g)) between TE and Delta (r(g) = -0.87, P < 0.001) was observed in glasshouse studies. Gas exchange measurements of field grown plants indicated that Delta was strongly correlated with stomatal conductance to water vapor (g), (r(g) 0.64, P < 0.01), and the ratio of net assimilation rate (A) to g, (r(g) = 0.86, P < 0.001), an instantaneous measure of TE. Genotype CMSHA89MAX1 had the lowest TE (and highest Delta) of all genotypes tested in these studies and low yields in hybrid combination. Backcrossing studies showed that the TE of this genotype was due to an adverse effect of the MAX1 cytoplasm, which was inherited from the diploid perennial H. maximiliani Schrader. Overall, these studies suggested that there is an excellent opportunity for breeders to develop sunflower germplasm with improved TE. This can be achieved, in part, by avoiding cytoplasms such as the MAX1 cytoplasm.

Incidence of Stagonospora meliloti and Acrocalymma medicaginis in Lucerne crowns and roots in eastern Australia, and their comparative aggressiveness to Lucerne and inheritance of reaction to S. meliloti in lucerne

The research presented indicates that lucerne crown and root rot caused by Stagonospora meliloti is prevalent in southern New South Wales, whereas Acrocalymma medicaginis is the more commonly observed pathogen in Queensland. Although both pathogens cause reddening of internal root and crown tissue of lucerne, they can be distinguished by symptomatology. S. meliloti causes a diffuse red blotching of the internal tissue accompanied by the presence of an external lesion, whereas A. medicaginis causes red streaking at the extremity of wedge-shaped, dry-rotted tissue. Inoculation of propagules of a susceptible lucerne clone indicated that S. meliloti was the more aggressive pathogen. Although A. medicaginis does not cause leaf disease, there was a strong relationship between the leaf and root reaction of clones to S. meliloti. Inheritance of resistance to S. meliloti in lucerne appeared to be conditioned by a single dominant gene, based on segregations observed in S-1 and F-1 populations, but not in a backcross population from the same family where an excess of susceptible individuals (74% v. expected of 50%) was obtained in a cross of a resistant F-1 individual to the susceptible parent. Resistance appears to be highly heritable, however, and amenable to population improvement by breeding. A conclusion of the research is that breeding for resistance to S. meliloti for lucernes to be grown in southern Australia would appear to be a worthwhile objective. Presently, no highly resistant cultivars exist anywhere in the world.

Inheritance of proportionate dwarfism in Angus cattle

Objective To determine the mode of inheritance of congenital proportionate dwarfism in Angus and Angus crossbred cattle, initially detected in two commercial beef herds in northern New South Wales. Design Matings of normal carrier sires to unrelated cows of diverse breeds, and of one carrier sire to his unaffected daughters. An unrelated Piedmontese bull was also mated to unaffected daughters of the carrier sires. Procedure Two carrier Angus bulls and nine unaffected daughters, all of whom were completely indistinguishable from normal animals, were purchased for controlled breeding studies under known nutritional and disease conditions. Affected and carrier individuals were examined for the presence of obvious chromosomal abnormalities. Results Angus dwarfism has been successfully reproduced under controlled experimental conditions over successive years using unrelated dams and is undoubtedly heritable. The high frequency of occurrence of affected individuals (23/61 = 0.38 +/- .06) among the progeny of matings of the Angus sires to unrelated females of diverse breeding is not compatible with recessive inheritance, because of the negligible frequency of proportionate dwarfism in the breeds of the dams. Both paternal and maternal transmission of the defect was demonstrated, so that imprinting in the strict sense of a gene that is only expressed when received from the male parent appears not to be involved. Tested individuals showed no evidence of gross chromosomal abnormality. Dominant autosomal inheritance with incomplete penetrance was indicated by the lack of expression of the defective gene in the two Angus sires and in three unaffected daughters who produced dwarf calves from matings to the Piedmontese bull. Conclusions The mode of inheritance is that of a single autosomal dominant gene with a penetrance coefficient of 0.75 +/- 0.12, estimated from the observed incidence of 23/61 affected offspring of the two carrier Angus bulls mated to unrelated dams. Simple genetic models involving either (i) an unstable mutant which changes at high frequency to the expressed dominant dwarfing allele during gametogenesis, or (ii) a dominant allele with penetrance determined by an unlinked modifying locus, are shown to be compatible with the experimental data. Both models indicate that penetrance of the dwarfing gene may possibly be higher in matings involving carrier daughters of the two Angus bulls.

Transpiration efficiency in a segregating population of sunflower: Inheritance, correlation with other traits and association with hybrid grain yield

Plants incorporate isotopes of carbon into their tissue at different rates because of discrimination against 13C relative to 12C during photosynthesis. This difference in discrimination has been negatively correlated with transpiration efficiency (TE) in many C3 species and so, carbon isotope discrimination (Δ) of leaf tissues has been proposed as a potential tool for selecting genotypes with improved performance under water limited conditions. The relationship between Δ and TE in sunflower has been described previously using diverse genotypes, but this relationship has not been investigated with material selected from a segregating population. In this study, the TE of twenty recombinant inbred lines from a population (HAR4 x SA52) segregating for Δ was evaluated in a rainout shelter experiment. A strong negative genetic correlation between TE and Δ was observed (rg = -0.58), confirming previous studies of sunflower with unrelated lines. In addition, TE was strongly correlated to plant height at the final harvest (rg = 0.64) and TDW (rg = 0.58), and moderately correlated to SLW (rg = 0.46) and SPAD (rg = 0.21) but not leaf number (rg = 0.02). Estimates of narrow sense heritability of TE and Δ were very high (0.82 and 0.77, respectively) suggesting that selection for these traits could occur in early generations of segregating populations. Grain yield evaluations under field conditions of hybrids contrasting for Δ showed that low Δ (high TE) hybrids had a yield advantage between 22-35% in dry environments where the yield was less than 2t/ha. While this level of yield advantage may not be realized in commercial breeding programs, computer simulations suggest that 10-15% yield improvements may be possible. Low Δ material selected from the population HAR4 x SA52 has been distributed to private seed companies for further evaluation.

Genetics of ocular disease Part 1: Basic concepts: cells, chromosomes and inheritance

This series of articles describes the basic elements of genetics necessary to understand the new advances and the impact these advances will have on the study and treatment of ocular disease. The first article describes the patterns of inheritance of human characteristics, how they are transmitted between the generations and the structure of chromosomes.

Genetics of ocular disease Part 3: Patterns of inheritance of ocular disease

The objective of this article is to describe the patterns of inheritance exhibited in the human populations and to illustrate them with examples drawn from a variety of ocular diseases.

Access Rights Inheritance in Information Systems Controlled by Metadata

All information systems have to be protected. As the number of information objects and the number of users increase the task of information system’s protection becomes more difficult. One of the most difficult problems is access rights assignment. This paper describes the graph model of access rights inheritance. This model takes into account relations and dependences between different objects and between different users. The model can be implemented in the information systems controlled by the metadata, describing information objects and connections between them, such as the systems based on CASE-technology METAS.