a. Water:
Water is a basic requirement for germination. It is essential for enzyme
activation, breakdown, translocation and use of reserve storage materials.
b. Oxygen:
atmospheric air is composed of 79.9 % Nitrogen, 20% oxygen and 0.03 % carbon
dioxide. Oxygen is required for germination of most of species. If
CO2 concentration is higher than 0.03 % it retards germination. Respiration
increases sharply during seed germination. Since respiration is essentially
an oxidative process, an adequate supply of oxygen is a must.
c. Temperature:
Seed germination is a complex process involving many individual reactions and
phases, each of which is affected by temperature. The effect on
germination can be expressed in terms of cordial temperature i.e., minimum,
optimum and maximum temperature. The optimum temperature for most of the seeds
is between 15 to 30 0C. maximum temperature is between 30 to 400C.
Some species will germinate even at freezing point also ex. Alpine
d. Light:
Some species required light for seed germination. Both light intensity
(lux) and light quality (colour and wavelength) influence seed germination
e.
Soil factor:
Soil structure, soil texture and soil temperature influences on seed germination
a. Impermeability of seed coat to water: due to seed coat structure, which is hard enough to
restrict the entry of moisture into the seeds, thereby preventing seed
germination. Ex: Malvaceae, Leguminoseae, Lilaceae
b. Impermeability of seed coat to gases; is related to the insufficient intake of oxygen by seeds due
to impermeability of seed structure enclosing embryo. Ex: Graminaceae, fruit
crops & forest trees
c. Mechanical resistances of seed coat: growth of embryo is checked due to extremely hard
seed/fruit structure such as seed coat, endosperm per carp etc., Ex: Acacia
species.
d. Inhibitors present in seed coat/endosperm: biochemical substances present in seed coat or endosperm
block the germination of embryo.