The causes and consequences of variation in silicon accumulation among wheat landraces

Silicon (Si) has long been regarded as a beneficial element for plants and is associated with improved stress tolerance. However, species vary in their ability to accumulate Si, which impacts on the benefits conferred from applying Si fertiliser in agriculture. Si accumulation likely also varies among genotypes within a species, but this possibility has not yet been extensively investigated. Wheat is an important staple food crop and known Si accumulator. In this study, significant differences in Si accumulation between wheat landraces were identified, allowing for the classification of high and low Si accumulating landraces. Whether the responses to varying levels of external Si, damage, osmotic stress, and drought varied between these two categories was then investigated. Overall, this study highlights the importance of considering genotypic variation when examining the potential effects of applying Si fertiliser in agriculture. Significant differences in Si accumulation between wheat landraces were found at all levels of Si availability (Chapter 2). These differences were partially attributed to differences in transpiration rate and were not correlated with genetic differences or variation in putative Si transporter gene expression. Si did not affect spine density, but there was a negative correlation between Si accumulation and growth (Chapter 2). In Chapter 3, repeated damage caused a localised increase in Si concentration only in damaged leaves, although damage did not affect the density of silicified spines. The localised increase in Si was comparable among all landraces and required a minimum of two damage events. The expression of jasmonic acid-related genes was unaffected by Si. In Chapter 4, Si caused a small increase in osmotic stress tolerance for both high and low Si accumulating landraces. However, Si did not significantly improve growth or yield during drought for any landrace. Osmotic stress decreased Si accumulation for all landraces whereas drought increased it.