Seeds are, with most species of agricultural interest, the main mechanism of reproduction. Seeds consist of an embryo and reserve compounds (carbohydrates, proteins, lipids), both surrounded by seed coatings. However, this general structure varies among the different species mainly in relation to the type and proportion of the reserve compounds and the characteristics of the seminal coatings.
The seeds, once their development on the mother plant has been completed, remain in a state of «rest» until favorable conditions for germination occur. This state can be determined by the existence of unfavorable environmental conditions or by the existence of factors that act from the seed itself, preventing its germination. In the first case it is said that the seed is in a state of quiescence and in the second case that the seed is dormant. The imbibition of quiescent seeds, under optimal conditions of temperature, oxygenation, and illumination, sets in motion a set of physiological mechanisms that allow their germination and the subsequent development of the seedling.
Germination begins with the entry of water into the seed (imbibition) and ends with the beginning of radicle elongation. Under laboratory conditions, the subsequent rupture of the seed coat by the radicle is the event used to consider that germination has taken place (physiological criterion). However, under field conditions, germination is not considered to be complete until the emergence and development of a normal seedling occurs (agronomic criterion).
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