Novel genotypes of the subtropical grass Eragrostis curvula for the study of apomixis (diplospory)

The aim of this work was to obtain a series of genetically related lines of Eragrostis curvula with different ploidy levels and reproductive modes, which can be used for the discovery of genes associated to diplospory. E. curvula is a widely cultivated forage grass native to Southern Africa that reproduces naturally by obligate diplosporous apomixis (asexual reproduction by seeds) of the Antennaria type. In vitro culture of immature inflorescences of the apomictic cultivar Tanganyika led to the regeneration of a diploid plant with a particular morphology (plant UNST1122). Embryo sac analysis and progeny tests determined that plant UNST1122 reproduces by sexuality. UNST1122 was cloned by dividing its tillers and a R ₁ generation was obtained from seeds after open pollination among the diploid clones. A set of 500 seeds from a diploid R ₁ plant was treated with colchicine and two plants showing a duplicated chromosome number (2n = 4x = 40) were obtained (plants UNST1112 and UNST1131). Progeny tests using RAPDs indicated that these plants reproduce also by sexuality. The availability of sexual tetraploid genotypes of E. curvula will allow the production of hybrids with new interesting combinations of agronomic traits and the developing of mapping populations segregating for diplospory. Besides, these genetically related plants with different reproduction modes constitutes an excellent model for the identification of gen(es) involved in diplosporous apomixis by mRNA profiling as well as to study the genomic rearrangements and gene expression alterations associated to changes at ploidy levels.     

Risk characterisation and management of sewage sludge on agricultural land-implications for the environment and the food-chain

The disposal of sewage wastes may cause severe environmental problems as was graphically demonstrated with pollution on Sydney's ocean beaches in recent years. Sewage sludges contain valuable plant nutrients and organic matter which can improve the fertility and structure of the soil. However, human parasites, pathogenic micro-organisms and chemicals capable of causing soil contamination, phytotoxicity and residues in animal products may also be present. Although sewage sludge is frequently spread on agricultural land overseas, it is not common in Australia and most states do not have specific regulations to minimise risk and promote good practice. A sludge-to-land program began in the Sydney region in 1990. It follows guidelines written by NSW Agriculture to encourage beneficial agricultural use of sludge by adoption of environmentally sustainable practices. This article describes the major risks to the food-chain and the environment, which may be associated with applying sewage sludge to agricultural land. It summarises how the risks are managed, and where further research data are required.     

Bovine thyroglobulin gene polymorphisms and their association with sexual precocity in Guzerat bulls

Puberty is a stage of sexual development determined by the interaction of environmental factors and genetic mechanisms. Among them, thyroid function plays a key role in sexual development and spermatogenic function and is under the control of several genes, including the well‐described thyroglobulin gene (TG). Previous reports have shown genetic association between thyroid function and selected single nucleotide polymorphisms (SNPs) in taurine cattle. Therefore, the identification of genetic mechanisms involved in the regulation of this trait can assist with the selection for early pubertal bulls, thus improving genetic progress in livestock breeding. The aim of this study was to validate the association between TG SNPs and age at puberty in zebuine bulls. Three SNPs (rs110406764, rs109662686, rs109057985) were genotyped in 159 Guzerat animals using SEQUENOM technology. Results showed a significant association (p < .05) between the studied SNPs and puberty age, in agreement with our previous reports in a taurine breed. Interestingly, allele frequencies were different from those already reported, being GAT the most favourable allele for age at puberty in Guzerat (94.4 days lower). Overall, our findings corroborate previous reports and reinforce the importance of genetic influence in the regulation of sexual development and puberty through a thyroid pathway in zebuine cattle.     

A free-fall determination of the newtonian constant of gravity

Recent determinations of the Newtonian constant of gravity have produced values that differ by nearly 40 times their individual error estimates (more than 0.5%). In an attempt to help resolve this situation, an experiment that uses the gravity field of a one-half metric ton source mass to perturb the trajectory of a free-falling mass and laser interferometry to track the falling object was performed. This experiment does not suspend the test mass from a support system. It is therefore free of many systematic errors associated with supports. The measured value was G = (6.6873 +/- 0. 0094) x 10(-11) m3 kg-1 sec-2.     

Thermographic selection of effective catalysts from an encoded polymer-bound library

A general method is introduced for the rapid and simultaneous evaluation of each member of large encoded catalyst libraries for the ability to catalyze a reaction in solution. The procedure was used to select active catalysts from a library of potential polymer-bound multifunctional catalysts. From approximately 7000 beads screened (3150 distinct catalysts), 23 beads were selected for catalysis of an acylation reaction. Kinetic experiments indicate that the most strongly selected beads are also the most efficient catalysts.     

Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 1. Patterns of seasonal development

Abstract

AIM: To describe the seasonal pattern of development of third-stage infective larvae (L3) from eggs of Teladorsagia (=Ostertagia) circumcincta, Trichostrongylus colubriformis and Haemonchus contortus on pasture in the North Island of New Zealand.

METHODS: Sheep faeces containing known numbers of eggs of all three nematode species were deposited on, or buried in, pasture plots at three sites, viz coastal Manawatu, Upper Hutt Valley, and East Cape hill country. Development was measured by recovering L3 from faeces, herbage and soil 28–31 days after deposition on 13–18 occasions, between January 2005 and July 2006. Analysis of the number of larvae recovered used a mixed model including number of eggs deposited, weight of faeces recovered (an assumed indicator of earthworm activity), site, contamination date, and position of deposited faeces, i.e. on the surface or buried.

RESULTS: There was a significant effect of contamination date on development of all three species, with maximum numbers ofL3 developing between late spring (November) and early autumn (March), and minimum numbers in June and July. There were large differences between species, with H. contortus exhibiting a long period (April to October) where development was close to zero, whereas T. circumcincta developed to some extent all year round. Development of T. colubriformis was intermediate between the other two species.

Burying faeces containing nematode eggs increased the number of L3 recovered compared with surface deposition (p≤0.001), although there were a small number of exceptions involving only T. colubriformis. The weight of faeces recovered at harvest, which was assumed to be an indication of earthworm activity, was correlated with the number of L3 recovered for all species (p<0.001). In a separate analysis, earthworms were assumed tohave been active if <5 g faeces remained at harvest. Where this occurred, the number of L3 of T. colubriformis and T.circumcincta recovered was reduced by 56% and 58%, respectively (p<0.001).

CONCLUSIONS: A marked seasonal pattern of development was observed for all three species, with the most larvae developing in spring-early autumn and the least in winter. This seasonal pattern was most pronounced in H. contortus and least obvious in T. circumcincta. Burying faeces containing eggs generally resulted in more L3 being recovered, whilst the apparent activity of earthworms resulted in fewer larvae being recovered.     

Calm Temperament Improves Reproductive Performance of Beef Cows

Profitability of a beef operation is determined by the proportion of cows attaining pregnancy early in the breeding season and those that are pregnant at the end of breeding season. Many factors, including temperament, contribute to those reproductive parameters. The objective of this study was to evaluate effects of temperament on reproductive performance of beef cows. In Experiment 1, Angus and Angus‐cross beef cows (n = 1546) from eight locations were assigned a body condition score (BCS; 1 = emaciated; 9 = obese) and chute exit and gait score (1 = slow exit, walk; calm temperament; 2 = jump, trot or run; excitable temperament). Cows were grouped with bulls (1 : 25 to 1 : 30; with satisfactory breeding potential and free of venereal disease) for an 85‐day breeding season. Pregnancy status and stage of gestation were determined (transrectal palpation) 35 days after the end of the breeding season. Controlling for BCS (p < 0.01) and handling facility (p < 0.0001) and handling facility by temperament score interaction (p < 0.001), breeding season pregnancy rate was lower in excited versus calm cows [88.6% (798/901) vs 94.1% (607/645); p < 0.001]. Cows with an excitable temperament took 24 more days to become pregnant compared to calm cows (median days to pregnancy, 35 vs 59 days; p < 0.0001). In Experiment 2, Angus and Angus‐cross beef cows (n = 1407) from 8 locations were assigned scores for body condition and chute exit and gait (as described in Experiment 1) and assigned to bulls (breeding sound and free of venereal disease; 1 : 25 to 1 : 30) for 85 days. Pregnancy status was determined by transrectal palpation at 2 and 6 months after the onset of the breeding season. Controlling for BCS (p < 0.05), pregnancy loss was higher in excited versus calm cows [5.5% (36/651) vs 3.2% (20/623), p < 0.0001]. In conclusion, beef cows with an excitable temperament had significantly lower reproductive performance than calmer cows. The modified two‐point chute exit–gait scoring method was repeatable and identified cattle with an excitable temperament.