Pre-sowing seed treatment - A shotgun approach to improve germination, plant growth, and crop yield under saline and non-saline conditions

Rapid seed germination and stand establishment are critical factors to crop production under salt-stress conditions. In many crop species, seed germination and early seedling growth are the most sensitive stages to salinity stress. Salinity may delay the onset, reduce the rate, and increase the dispersion of germination events, leading to reductions in plant growth and final crop yield. The adverse effects of salt-stress can be alleviated by various measures, including seed priming (a.k.a. pre-sowing seed treatment). The general purpose of seed priming is to partially hydrate the seed to a point where germination processes are begun but not completed. Most priming treatments involve imbibing seed with restricted amounts of water to allow sufficient hydration and advancement of metabolic processes but preventing germination or loss of desiccation tolerance. Treated seeds are usually redried before use, but they would exhibit rapid germination when re-imbibed under normal or stress conditions. Various seed priming techniques have been developed, including hydropriming (soaking in water), halopriming (soaking in inorganic salt solutions), osmopriming (soaking in solutions of different organic osmotica), thermopriming (treatment of seed with low or high temperatures), solid matrix priming (treatment of seed with solid matrices), and biopriming (hydration using biological compounds). Each treatment has advantages and disadvantages and may have varying effects depending upon plant species, stage of plant development, concentration/dose of priming agent, and incubation period. In this article, we review, evaluate, and compare effects of various methods of seed priming in improving germination of different plant species under saline and non-saline conditions. We also discuss the known metabolic and ultra-structural changes that occur during seed priming and subsequent germination. To maximize the utility of various seed priming techniques, factors affecting their efficiency must be examined and potential benefits and drawbacks determined. For example, quality of the seed before treatment, concentration/dose of priming agent, time period for priming, and storage quality of the seed following priming treatment must be carefully determined. Furthermore, such assessments must be based on large-scale experiments if seed priming is to be used for large-scale field planting. A better understanding of the metabolic events that take place in the seed during priming and subsequent germination will improve the effective application of this technology. The incorporation of advanced molecular biology techniques in seed research is vital to the understanding and integration of multiple metabolic processes that can lead to enhanced seed germination, and consequently to improved stand establishment and crop yield under saline and non-saline conditions. (c) 2005, Elsevier Inc.