Seed enhancement-Definition Seed invigoration or seed enhancements are “post-harvest” treatments to improve germination and seedling growth or help in the provision of seeds and other materials required at the time of sowing. (Taylor et al., 1998)
Seed enhancements -objectives Improve germination/seedling growth through manipulation of seed vigor or physiological status Hydration trts (priming, steeping, hardening, pregermination). Chemicals to trigger stress tolerance. Antioxidants Facilitate seed planting (pelleting, coating, encrusting). Deliver materials needed at sowing (e.g. nutrients, inoculants).
Cont…… Remove weak or dead seeds using nontraditional ‘upgrading’ techniques (density, color sorting etc). Better adaptation to less than optimum conditions crops can compete more effectively with stresses and weed. ‘Tagging’ of seeds with visible pigments or other Materials for traceability and identity Preservation.
Why Treat Seeds? Higher yield Often pays for itself Improved crop quality A safeguard against disease Pest protection with lower environmental impact A smart way to apply anti-pest products Smooth machinery operation Easier handling
Seed Enhancement Priming Thermal treatment Coating / pelleting Hydropriming Dry heat treatment Pre-sowing Chilling Osmopriming Matripriming Humidification Osmohardening Hormonal priming On farm priming Hardening
Thermal Treatments Heat Treatments Control the external and internal seed-borne pathogens, including fungi, bacteria, viruses, and nematodes (Nakagawa 1989; Fourest et al., 1990). Break the dormancy of seeds (Zhang, 1990; Dadlani and Seshu, 1990).
Cont….. B. Pre-sowing chilling Also called cold stratification. Cold treatment releases the dormancy and enhance plant tolerance to salt stress. The beneficial effects of cold stratification could be attributed to ionic homeostasis and hormonal balance (Sharma and Kumar, 1999; Iqbal and Ashraf, 2007, 2010)
Seed priming: (A simple low cost solution) Seeds are hydrated in a controlled manner to provide enough water to initiate the metabolic processes of germination, but not enough to allow germination to be completed.” Improvements in germination speed and/or uniformity common with primed seed lots.
Hydropriming Seed soaking in tap water (with or without aeration) and re-drying to original weight (Soon et al., 2000, Farooqet al., 2006). No chemical is used. Environmently safe
On-Farm Seed Priming Farmers can prime their own seeds. Seeds are soaked in clean water, usually overnight (about 8-12 hours). After soaking, the water is drained off and the seeds are surface-dried by placing them on a cloth or plastic sheet on the ground for 15 to 30 minutes.
Soaking Period Recommended safe limits tested in over 100 farm trials (with only minor differences depending on variety and country) include: Rice: 24 hours Wheat and Barley: 12 hours Upland Rice and Maize: 16 to 18 hours Sorghum and Pearl Millet: 10 hours Chickpea and Mungbean: 8 hours
B. Hardening Repeated soaking of seeds in (aerated) water and re-drying. This hydration-dehydration cycle may be repeated twice, thrice and so on (Lee and Kim, 2000, Farooqet al. 2004).
Osmopriming (osmoconditioning) Seeds are incubated in well aerated solutions with a low water potential, and afterwards washed and dried. PEG is preferred osmoticum due to large molecular size and inert form which precludes it from being taken up by the embryo.
Halopriming Soaking of seeds in salt solutions was proposed as alternative to priming which enhanced germination and increase seedling emergence uniformity under adverse environmental conditions. Commonly using salts are NaCl, KNO3, CaCl2.
Hormonal priming Soaking of seeds in an appropriate concentration of hormones (GA, Auxin, Kinetin, Salicylic acid) before radicle protrusion.
Matrix priming (Matriconditioning) “Incubation of seeds in a solid, insoluble matrix (vermiculite, diatomaceous earth) with a limited amount of water.” Solid matrix carriers e.g. Micro CellE®, Celite, Press mud, Jute mat, Peat soil, compost
Seed Priming Effects on Germination Rates Seed priming generally reduces the time to radicle emergence and the spread in time over which germination occurs.
Coating Application of materials to the seed surface, often containing seed protectants such as fungicides. A major advantage of film coating is reduced loss of active material from the seed during seed transport and handling.
Seed Pelleting Inert materials are added to change seed size and shape for improved plant ability.” Used to round out small or irregular shaped seed, or to make small seeds larger – improves singulation and speed of sowing.
Cont…… Seed in rotating drum is wetted, and blends of powdered materials (e.g. chalk, clays, perlite, lime, peat, talc) plus water-attracting or hydrophobic materials are progressively added, along with more water, until desired pellet wt or size increase is achieved. Wet-coated seed then dried with air, usually in separate equipment.
Encrusting Addition of a small amount of material to a seed to enable accurate mechanical seed metering. Encrustment is most often used on crops that benefit from seed singulation but don’t require post-emergence thinning. Encrusting adds more weight to the finished product than film coating and significantly less weight than pelleting. Apply a minimum amount of filler materials and binders, whist still increasing the size of the seed, and filling out any irregular shapes and surfaces.
Pelleting vs. Encrusting Encrusting (aka ‘minipelleting’ or ‘coating’) applies less material,So the original seed shape is still(more or less) visible. When the added material is slight, the product may appear similar to film coated seed. Seed pelleting and encrusting techniques were commercially developed in the past 40-50 years, using techniques from confectionery and pharmaceutical industries.
Pre-germination Some seed enhancement technologies permit early germination to occur prior to sowing. Sprouted seeds are suspended in a gel, and sown by extrusion. Fluid drilling is one of these techniques
Cont…… Fully imbibed seeds germinated to point of visible radicles, then sorted and gradually dried to induce desiccation tolerance. Can produce damp pre-germ seeds with storage life of a few weeks at ambient temps, or dry pre-germseed (viable for a few months). Commercially available at present for high-value flower seeds only (e.g. Impatiens, pansy)(Halmer, 2006)
Conclusion Improve seed sowing, germination and seedling growth by altering the physiological state of the seed. Improve vigor or the physiological state of the seed by enhancing uniformity of germination. Enhance disease resistance in seeds. Enhance seed vigor and modify seed emergence capabilities. The seeds pelleted with different chemicals recorded significantly higher growth parameters over unpelletedseeds. Precise placement on the target . Minimum toxicant used. Minimum environmental impact . Minimum wildlife and other organism exposure.