Measuring Germination: The Radicand Germination Index. & A Biostimulant Seed Treatment: Mechanism and Optimization.
Application of seed treatments to enhance crop performance is an important practice in agriculture. Seed treatments are commonly applied to protect seeds from harmful pathogens, to provide mycorrhizae, or rhizobia bacteria. However, seed treatments may act as stimulants to germination and growth, which is a potential avenue for improving crop establishment and yield. In this thesis, we established treatment guidelines for spraying application of a biostimulant H2O2-FeSO4 catalytic seed treatment for alfalfa, hybrid bromegrass, carrot, sainfoin and wheat. To accurately assess the germination stimulating effects of the catalytic seed treatment, we explored various ways of quantifying germination, and surveyed the literature to determine typical practices. Ultimately, we discovered that the standard practices for the reporting of germination data are woefully inadequate, and lead to changes in germination speed, or uniformity being overlooked. The result of this inadequacy is that many papers may overlook significant trends in the data, thereby producing false negative results, due to their inability to differentiate between germination profiles. To remedy this issue, we developed the Radicand Germination Index (RGI), which accounts for germination speed, capacity, and uniformity, and can successfully differentiate between a representative array of germination profiles. Using RGI, and Arabidopsis mutants we explored the mechanisms which underlie the germination and growth stimulating properties of the seed treatment and identified the Abscisic Acid 8’- Hydroxylase gene CYP707A2, and de-novo synthesis of H2O2 through NADPH oxidase as key mechanisms driving the germination and enhanced lateral root growth responses to treatment. Furthermore, enhanced oxygen availability and nitric oxide production (NO) were identified as additional probable factors that underlie the treatment’s biostimulant properties. It was also discovered that the method of treatment application has a dramatic impact on its efficacy; with the effect size for sprayed seeds being reduced compared to soaked. A corollary of this is that the spraying experiments, designed based on the previously reported effect sizes determined by soaking, had insufficient samples to detect the effect of treatment applied by spraying. Thus, due to this failure in experiment design, the discussion of the results from spraying experiments focused primarily on effect sizes and trends, rather than significance.
Radicand Germination Index, RGI, Germination, Biostimulant Seed Treatment, Catalytic Seed Treatment
Master of Science (M.Sc.)