Seed Germination and Seedling Emergence

The effects of temperature and other factors on the germination of fescue seeds have been studied since the mid 1900s (Kearns and Toole, 1939). Optimal temperatures for tall fescue seed germination, as established by the Association of Official Seed Analysts (AOAC), are 20°C (68°F) for 16 h and 30°C (86°F) for 8 h. When seeding tall fescue turf, a planting rate of 19 to 43 g/m2 (4-9 lb/1,000 ft2) or more is often recommended (Emmons, 1995). This planting rate range is much higher than that recommended for pasture plantings (Pinkerton, 1999) and results in approximately 1 to 2 seeds/cm2 (~7-16 or more seeds/in2).

Germination begins as water is absorbed by the seed. Simple carbohydrates are produced as enzymes split starch stored in the endosperm into its component sugars. These enzymes are produced in the aleurone layer in response to hormones (giberrellins) produced in the scutellum. The scutellum absorbs carbohydrates from the endosperm. Carbohydrates eventually are transmitted to other parts of the embryo. The coleorhiza swells as cells elongate and hairlike structures emerge, anchoring the embryo to the soil. The primary root (radicle) breaks through the coleorhiza and moves into the soil. At about the same time that the radicle protrudes from the coleorhiza, the coleoptile, a pointed protective sheath covering the emerging shoot, reaches the soil surface. The coleoptile is translucent because it does not accumulate significant chlorophyll or carotenoids, and it stops growing upon reaching the soil surface. The first leaf then elongates and pushes out through a pore at the tip of the coleoptile. Since the growing point of the seedling is located within the coleoptile, the second leaf also grows through it, rolled inside the first leaf. Each successive leaf grows upward from the growing point within an older, enclosing leaf. Photosynthesis begins when a leaf is exposed to sunlight, and soon the tall fescue seedling is entirely dependent on this critical photochemical reaction for energy. A tall fescue seedling may have both primary (seminal) and adventitious (secondary, nodal) roots. Adventitious roots develop from nodes at the base of the new shoot and eventually become the permanent root system supporting the plant.

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