From seed to seedling - damping-off tolerance in Spinacia oleracea L

Abstract

Table of contents Chapter 1. General introduction Chapter 2. Sensitivity of spinach seed germination to moisture is driven by oxygen availability and influenced by seed size and pericarp Chapter 3. Evaluation of damping-off tolerance in spinach cultivars in field soils and in a standardised lab assay with Pythium ultimum Chapter 4. Rate of seedling emergence is not the only driver of pre-emergence damping-off tolerance in spinach Chapter 5. Higher seed maturity levels, darker pericarp, and smaller seed size relate to improved damping-off tolerance in spinach Chapter 6. General discussion Bibliography Summary Samenvatting Acknowledgements Biography Training and education statement General introductionChapter 1General introduction | 17 reflectance from the spinach seed pericarp has been shown to be a good marker for the presence of fungal infection of those seeds (Olesen et al., 2011). In addition, chlorophyll fluorescence (CF) of a seed can be measured by emitting light onto the seed at 450 or 660 nm and measuring excitation from the seed at 730 nm. CF has been demonstrated to be a good marker for the maturity level of seeds of many plant species, with an inverse correlation with germination (Jalink et al., 1998). Also, for sugar beet and spinach seeds, where CF is measured from the pericarp instead of the seed coat, CF correlated negatively with germination (Deleuran et al., 2013;Boelt et al., 2018). In this study, spectral and fluorescence measurements in addition to morphological measurements of spinach seeds are performed and, for the first time, related to damping-off tolerance. Chapter 2Uniform seedling emergence is crucial for economically viable spinach (Spinacia oleracea L.) production. However, non-uniform seed germination occurs due to variation in moisture sensitivity among and within spinach seed lots. To test moisture sensitivity, we developed a floating germination system with fixed distances between the water table and germination papers, so that moisture levels were standardised. We tested germination performance of different cultivar seed lots, with one seed lot fractionated into different seed sizes, and of seeds with an intact, open, or removed pericarp. At high moisture level, smaller seeds germinated better than larger seeds, and seeds without a pericarp or with an open pericarp germinated better than intact seeds. The pericarp of smaller seeds was relatively thinner than the pericarp of larger seeds. A lower temperature or increased oxygen level resulted in improved germination of differently-sized seeds at a high moisture level. In conclusion, the sensitivity of spinach seed germination to moisture is influenced by seed size, hence pericarp thickness and intactness, and is driven by oxygen availability to the seed embryo. To determine the full germination potential of spinach seed lots, we recommend a standardised low moisture level in addition to a temperature of 15 to 20°C.

Designing a Seed Health Strategy for Organic Cropping Systems, Based on a Dynamic Perspective on Seed and Plant Health

“…Although the effect may depend on the crop, the pathogen pressure and other field conditions, this demonstrated the potential advantage of high vigour seeds for farming. A study with spinach (Spinacia oleracea) seeds showed that smaller seeds with a thinner pericarp are less sensitive to high soil moisture conditions that limit oxygen diffusion [34], whereas less mature spinach seeds are more sensitive to the soil borne pathogen Pythium ultimum [35]. In the frame of the LIVESEED project we studied the effect of vigour on biotic stress tolerance using carrot seeds and the pathogen Alternaria radicina, which can cause seedling 'damping-off' by infecting and damaging the root system.…”