Fitting and comparing seed germination models with a focus on the inverse normal distribution

Assessing the Effect of Diesel Fuel on the Seed Viability and Germination of Medicago sativa Using the Event-Time Model

The remediation of contaminated sites using plant-based techniques has gained increasing attention in recent decades. However, information on the effects of contaminant imbibition on seed viability and germination rates are often lacking in the literature. To this end, our research investigated, by means of an event-time model, the effect of diesel fuel imbibition on the seed viability and germination rate of Medicago sativa, a plant species with great potential for remediation of organic contaminants. The event-time model provided an accurate and biologically relevant method for analysing germination data. Our results reveal that the direct imbibition of diesel fuel by M. sativa seeds for ≤48 h, or their exposure to soil diesel fuel concentrations of 0-10 g/kg diesel fuel, affects their germination rates, as shown by increasing t50 values from 90.6 (±2.78) to 114.2 (±2.67) hours, without significantly affecting seed viability. On the other hand, diesel fuel imbibition of longer duration, or the exposure of M. sativa seeds to ≥20 g/kg diesel fuel-contaminated soils, leads to no further effect on time to seed emergence. Instead, these conditions compromise seed viability, resulting in a decrease in the proportion of germinated seeds from 0.91 (±0.03) in 10 g/kg diesel fuel contaminated soil to 0.84 (±0.04) and 0.70 (±0.05) in 20 and 30 g/kg diesel fuel-contaminated soils, respectively. The fact that low concentrations of diesel fuel and 0-48 h of direct imbibition delayed seed emergence without adversely affecting the percentage of viable seeds suggests that this inhibitory effect on germination at low diesel fuel exposure could be attributed more to physical constraints rather than biological damage on the seeds. The models used in this study provide an accurate and biologically relevant method for the analyses of germination data. This is vital since expensive germination experiments, be it in the field of toxicology or agriculture, deserve to be accurately analysed.

Genetic mapping of a barley leaf rust resistance gene Rph26 introgressed from Hordeum bulbosum

The quantitative barley leaf rust resistance gene, Rph26, was fine mapped within a H. bulbosum introgression on barley chromosome 1HL. This provides the tools for pyramiding with other resistance genes. A novel quantitative resistance gene, Rph26, effective against barley leaf rust (Puccinia hordei) was introgressed from Hordeum bulbosum into the barley (Hordeum vulgare) cultivar 'Emir'. The effect of Rph26 was to reduce the observed symptoms of leaf rust infection (uredinium number and infection type). In addition, this resistance also increased the fungal latency period and reduced the fungal biomass within infected leaves. The resulting introgression line 200A12, containing Rph26, was backcrossed to its barley parental cultivar 'Emir' to create an F₂ population focused on detecting interspecific recombination within the introgressed segment. A total of 1368 individuals from this F₂ population were genotyped with flanking markers at either end of the 1HL introgression, resulting in the identification of 19 genotypes, which had undergone interspecific recombination within the original introgression. F₃ seeds that were homozygous for the introgressions of reduced size were selected from each F₂ recombinant and were used for subsequent genotyping and phenotyping. Rph26 was genetically mapped to the proximal end of the introgressed segment located at the distal end of chromosome 1HL. Molecular markers closely linked to Rph26 were identified and will enable this disease resistance gene to be combined with other sources of quantitative resistance to maximize the effectiveness and durability of leaf rust resistance in barley breeding. Heterozygous genotypes containing a single copy of Rph26 had an intermediate phenotype when compared with the homozygous resistant and susceptible genotypes, indicating an incompletely dominant inheritance.

Generalized logistic functions in modelling emergence of Brassica napus L

The objective of this study was to determine whether generalized logistic functions (Richards model with time shift) may be used to predict emergence of winter rapeseed (Brassica napus L.) after its seed treatment with plant extracts from Taraxacum officinale roots under controlled environment conditions. Emergence analyses were conducted for winter rape whose seeds were treated with a plant extract and for the non-treated seeds sown to the soil at the site of earlier point application of the extract. Curves were plotted for experimental data by minimizing the square sum of differences between the experimental data and the mathematical model. To evaluate model fit, the mean squared error was divided into four factors. Computing modelling efficiency coefficients were also introduced to enable complete analysis. Results of simulation research demonstrate that the determined parameters of curves (e.g. values of growth parameters, time shift or the upper limit of population) describing the number of seedlings in the function of time stayed compliant to the interpretation with regard to the biology of the analyzed processes. The proposed mathematical description based on generalized logistic functions showed extraordinary fit (r = 0.999) to the experimental data, which makes it highly useful in predictive control of rapeseed emergence. In addition, the study enabled concluding that plant extracts application to the soil allowed achieving a higher maximal emergence rate compared to the control sample. The application of the plant extracts increased the final population of rapeseed and significantly accelerated the occurrence of the maximal emergence rate.

Drying times of umbilical cords of dairy calves

OBJECTIVE

To determine the distribution of drying times of umbilical cords of dairy calves and to determine if cord dryness is a reliable indicator of age.

DESIGN

An observational study was undertaken in a spring calving herd in Victoria, of the umbilical cords of 188 calves (82 Friesian bulls, 82 Friesian heifers, 24 crossbreds).

PROCEDURE

Umbilical cords were examined daily, visually and by palpation, until the cord to the junction of the skin on the abdomen of the calf was dry, shrivelled and inflexible.

RESULTS

Drying times ranged from 1 to 8 days. By the fifth day of life, the umbilical cords of 96.7% of all calves, 97.5% Friesian heifer calves, 87.5% of Friesian bull calves and 100% of cross-bred calves were dry. If cord dryness only was used to select calves for sale, 91.3% of all calves, 86.4% of Friesian bull calves and 100% of cross bred calves could have been sold before their fifth day of life. If calves were selected on age only, 3.3% of all calves, 2.5% of Friesian heifer calves and 12.5% of Friesian bull calves would have been sold before their umbilical cord was dry.

CONCLUSION

The dairy industry cannot rely on cord dryness alone as an indicator of age for selection of calves for sale and transportation. Cord dryness is a poor indicator of age.

Comparative studies on salt tolerance of seedlings for one cultivar of puccinellia (Puccinellia ciliata) and two cultivars of tall wheatgrass (Thinopyrum ponticum)

Salt tolerances of 3 cultivars, Menemen puccinellia (Puccinellia ciliata Bor), Tyrrell and Dundas [tall wheatgrass, Thinopyrum ponticum (Podp.) Z. W. Liu and R. R. C. Wang], were compared with respect to their seed germination, adaptive responses to salt and waterlogging, seedling emergence, plant growth, shoot osmolality and mineral contents in a series of salt-stress experiments. An inverse normal distribution provided good fits for the time to seed germination. Under NaCl stress, 50% of the control (distilled water) seed germination rates of Menemen, Tyrrell and Dundas were achieved in 178.8, 300.9 and 296.8 mmol/L NaCl, respectively. Fifty percent of the control seedling emergence rates of these 3 cultivars were in 92.7, 107.2 and 113.5 mmol/L NaCl, respectively. The seed germination rates of these 3 cultivars under both salt and waterlogging stress were far lower than those germinated only under salt stress at the same salt level. Seed pretreatment by soaking seed in NaCl solutions greatly increased the seed germination rate under salt stress for Menemen and under both salt stress and waterlogging for Dundas. Tyrrell and Dundas were very similar in their tolerance to salt stress, and were significantly (P<0.05) more salt tolerant than Menemen in terms of seed germination and seedling emergence rate. Both shoot height and dry matter of these 3 cultivars were not statistically different among all salt stress levels during the seedling elongation period, indicating that the established plants of these 3 cultivars were very salt tolerant. The salt tolerance mechanisms of these 3 cultivars are possibly related to their abilities to maintain high osmolality in shoots by regulating high sodium and potassium contents, and reducing calcium deficiency under salt stress.