Seed priming in field crops: potential benefits, adoption and challenges

Seed priming is a presowing technique in which seeds are moderately hydrated to the point where pregermination metabolic processes begin without actual germination. Seeds are then redried to near their actual weight for normal handling. Seeds can be soaked in tap water (hydropriming), aerated low-water potential solutions of polyethylene glycol or salt solutions (KNO3, KH2PO4, KCl, NaCl, CaCl2 or MgSO4; osmopriming), plant growth regulators, polyamines (hormonal priming), plant growth-promoting bacteria (biopriming), macro or micronutrients (nutripriming) or some plant-based natural extracts. Here, we review: (1) seed priming as a simple and effective approach for improving stand establishment, economic yields and tolerance to biotic and abiotic stresses in various crops by inducing a series of biochemical, physiological, molecular and subcellular changes in plants; (2) the tendency for seed priming to reduce the longevity of high-vigour seeds and improve the longevity of low-vigour seeds; (3) the advantages of physical methods of seed priming to enhance plant production over conventional methods based on the application of different chemical substances; (4) the various physical methods (e.g. magneto-priming and ionising radiation, including gamma rays, ultraviolet (UV) rays (UVA, UVC) and X-rays) available that are the most promising presowing seed treatments to improve crop productivity under stressful conditions; and (5) effective seed priming techniques for micronutrient delivery at planting in field crops. Seed priming as a cost-effective approach is being used for different crops and in different countries to improve yield, as a complementary strategy to grain biofortification and in genetically improved crop varieties to enhance their performance under stress conditions, including submergence and low phosphorus. Some of the challenges to the broad commercial adaption of seed priming include longevity of seeds after conventional types of priming under ambient storage conditions and a lack of studies on hermetic packaging materials for extended storage.