Magnesium applications to growth medium and foliage affect the starch distribution, increase the grain size and improve the seed germination in wheat

Magnesium (Mg) has diverse functions in plants and plays a critical role in carbohydrate partitioning between source and sink tissues. There is, however, limited information available about the effects of Mg deficiency on grain starch accumulation, yield formation and seed quality in terms of seed germination and seedling establishment in wheat. In a solution culture experiment, bread wheat (Triticum aestivum) was grown to maturity with low or adequate Mg under greenhouse conditions, and a post-anthesis foliar Mg application was tested on low-Mg plants. The effects of these Mg treatments on i) yield parameters, ii) distribution of starch among sink and source organs, iii) tissue concentrations of Mg and other minerals and iv) seed germination and seedling development were investigated. Low Mg supply did not affect the vegetative biomass production; but substantially reduced the grain yield. Post-anthesis foliar Mg spray significantly minimized yield losses caused by Mg deficiency. Decreases in grain yield by Mg deficiency were due to decreases in individual seed weight rather than seed number per spike. Low Mg depressed the grain and root starch levels, while increasing the leaf starch. Foliar Mg spray largely reversed these effects of Mg deficiency. Seeds obtained from low-Mg plants exhibited severe impairments in germination and seedling establishment. These seed quality traits were also greatly improved by foliar Mg application to maternal plants. Magnesium deficiency reduces grain yield in wheat mainly by limiting the carbohydrate supply to developing seeds and thus by decreasing the seed weight. Since vegetative growth is far less affected than yield formation, Mg deficiency may remain latent until seed-filling. Therefore, foliar Mg application appears to be a promising tool to alleviate Mg deficiency during seed-filling and minimize its impact on yield and seed quality.