Germination Data Analysis by Time-to-Event Approaches

San Diego Thornmint (Acanthomintha ilicifolia) Populations Differ in Growth and Reproductive Responses to Differential Water Availability: Evidence from a Common Garden Experiment

The responses of rare plants to environmental stressors will determine their potential to adapt to a rapidly changing climate. We used a common garden approach to evaluate how six populations of the annual San Diego thornmint (Acanthomintha ilicifolia Lamiaceae; listed as endangered in the state of California and as threatened by the US Fish and Wildlife Service) from across the species range respond in terms of growth (biomass, height, and width) and reproduction (seed production, floral production, and next generation seed viability) to experimental differences in water availability. We found a significant irrigation-by-population interaction on the aboveground growth, wherein the differences in the magnitude and direction of treatment did not correlate directly with climate variables in natural populations. With respect to reproduction, the low-irrigation treatment produced more seeds per plant, more reproductive individuals, and a larger proportion of viable seed in most, but not all, populations. The seed production and the effect of irrigation on seed production correlated positively with rainfall at wild source populations. These results suggest that Acanthomintha ilicifolia responds to water limitation by creating more and higher-quality seed, and that plants locally adapted to a higher annual rainfall show a greater plasticity to differences in water availability than plants adapted to a lower annual rainfall, a finding that can inform the in situ demographic management and ex situ collection strategy for Acanthomintha ilicifolia and other rare California annuals.

A successive time-to-event model of phyllochron dynamics for hypothesis testing: application to the analysis of genetic and environmental effects in maize

BACKGROUND

The time between the appearance of successive leaves, or phyllochron, characterizes the vegetative development of annual plants. Hypothesis testing models, which allow the comparison of phyllochrons between genetic groups and/or environmental conditions, are usually based on regression of thermal time on the number of leaves; most of the time a constant leaf appearance rate is assumed. However regression models ignore auto-correlation of the leaf number process and may lead to biased testing procedures. Moreover, the hypothesis of constant leaf appearance rate may be too restrictive.

METHODS

We propose a stochastic process model in which emergence of new leaves is considered to result from successive time-to-events. This model provides a flexible and more accurate modeling as well as unbiased testing procedures. It was applied to an original maize dataset collected in the field over three years on plants originating from two divergent selection experiments for flowering time in two maize inbred lines.

RESULTS AND CONCLUSION

We showed that the main differences in phyllochron were not observed between selection populations but rather between ancestral lines, years of experimentation and leaf ranks. Our results highlight a strong departure from the assumption of a constant leaf appearance rate over a season which could be related to climate variations, even if the impact of individual climate variables could not be clearly determined.

Effect of Microalgal Extracts from Chlorella vulgaris and Scenedesmus quadricauda on Germination of Beta vulgaris Seeds

Sugar beet (Beta vulgaris subsp. vulgaris) is a commercially important biennial root crop, providing about 20% of the world's annual sugar production. Seed quality is crucial for adequate plant growth and production. The productivity of sugar beet is often limited by heterogeneous germination in the field. In order to improve the sugar beet germination process, the effect of different concentrations of microalgal extracts from Chlorella vulgaris or Scenedesmus quadricauda was investigated by calculating several indices useful to evaluate the germination performance. Moreover, root morphological analysis was performed by using WinRHIZO software. B. vulgaris seeds were soaked with five different concentrations (from 0.1 to 10 mg C_org/L) of the microalgal extracts, considering the amount of organic carbon (C_org) in each extract. Our results show that these microalgal extracts exert a positive effect on sugar beet germination, by increasing efficiency and regularity of this critical process for B. vulgaris seeds. The best results, in terms of germination indices as well as root morphological traits, were reached by using C. vulgaris extract at the concentrations C2 (1 mg C_org/L) and C3 (2 mg C_org/L).