Reasons for seeds failed

                                                                             

Several reasons have been proposed to be responsible for the death of seed that includes:

• Breakdown in the mechanisms triggering germination hormones in general and especially and cytokinins are said to breakdown with deterioration. When these were added to highly deteriorated seed, improvement in germination was noticed; experimentally rapeseed exposed to ethylene produced normal seedlings                                                                                              
• Accumulation of toxic compounds, Hormones like abscisic acid and coumarin are said to accumulate in deteriorated seeds these are known to inhibit germination                                             
• Starvation of meristematic cells, During respiration, energy exhaustion takes place especially at growing points. Seeds lose the capacity to convert ADP  to ATP                                                     
• The inability of the ribosome to dissociate, Protein synthesis is a very essential step prior to germination. Polyribosomes must dissociate before being attached to RNA prior to the accumulation of protein reserves that can take place. In deteriorated seed, these ribosomes  fail  to dissociate                                                                                                                                          
• Enzyme degradation and inactivation, Enzymes such as catalase, dehydrogenase and glutamic acid decarboxylase are reported to decline with the ageing process                                                      
• Other factors such as genetic degradation and fungal invasion have been suggested as direct causes of deterioration                                                                                                                                                                                                                                                                                     Practical causes of deterioration.                                                                                                  a) Environment conditions and field management prior to harvest: This pose the greatest threat to the quality of seed and its longevity. One seed deterioration begins in the field nothing can be done to improve the situation.                                                                                                                                                                                                                                                               b) Abuse and mechanical damage during harvesting, processing, and handling.                                                                                                                                                                                       c) Temperature and humidity: High temperatures and humidity are other major causes of seed deterioration. Here relative humidity plays a great role in seed deterioration, both in the field and storage.                                                                                                                                                                                                                                                                                                 d) Time: Imposes the greatest unforeseen threat. With time any living material has a beginning and ending point.                                                                                                                                                                                                                                                                      Seed germination, viable seeds start to germinate when provided with appropriate conditions of moisture, temperature, and oxygen and in some cases light. However, not every seed brought into contact with good germination conditions will germinate. If such a seed is not dead, it is dormant. Dormancy is induced by any morphological or physiological barrier, which prevents germination.  The germination processes are divided into three phases:                                                                1) Imbitions phase                                                                                                                            2) Saturation phase (lag period)                                                                                                      3) Growth phase                                                                                            
• Imbibition(phase 1), The seed, first imbibe water, the tissues swell and the seed coat becomes soft and elastic. When the seeds imbibe water, various substances -gasses, salts, sugar- are driven out and their uptake increases. Oxygen is necessary for the breakdown of food reserve.                
• Saturation (phase 11), During this phase, preparation for germination takes place whereby mobilization of food reserves starts after the onset of germination. The reserve food is mainly meant for the growth of the seedling.                                                                                                                                                                             
• Growth( phase 111), The swelling of the seed by imbitions causes the testa to split open easing growth. Depending on the species, visible germination can occur several hours or days after imbibition phase.                                                                                                                               During germination the primary root pierces the seed coat and elongates rapidly, root hairs are usually abundant from the earliest stages. Later secondary roots are produced and the development of the shoot system follows.