Factors affecting germination of seed.

1. Water

• Water is absorbed initially by imbibition followed by absorption
• Imbibitional properties of seeds is found due to presence of colloidal materials which they contain especially protein and starch
• Seeds with impermeable seeds coats are to be soaked longer than those with permeable seeds coats
• But also, prolonged soaking may also adversely affect seed germination. For instance, soaking of barley seeds for 2-3 days decrease the rate of germination due to leaching out of metabolites

2. Temperature

• The optimum temperature required for seed germination shows variation from species to species
• The seeds of temperate plant relatively required low temperature as compared to tropical plants

3. Aeration

• Most seeds germinate at a oxygen level which is lower than the oxygen level present in the air
• But the oxygen requirement in germination phase of seeds is higher than the growing plants
• The high requirement of oxygen may due to presence of permeability barrier (seed coat)
• In general carbon dioxide reduces the percentage of germination

4. Light

• Germination of many seeds is affected by light, such seeds are called photoblastic seeds
• The seeds which germination is stimulated by light are called positive photblastic seeds

Example Amaranthus spp. , Nicotiania tobacum, Chenopodium spp.

• The seeds which germination is inhibited by light are called negative photoblastic seeds Example onion, lily etc
• Some seeds are irresponsive to light during germination Example tomato, cucumber etc.