Seed treatment and dormancy: Dormancy is the arrested development and reversible rest period of plant organs either of a seed or of any vegetative part. The formation of dormant structure is commonly associated with the suspension of metabolic, synthetic and morphogenetic activities that are associated with the minimum physiological and a minimum moisture content. During this period, there is very poor or total supension of respiration or rather anaerobic respiration with higher with higher respiration quotient.
Dormancy is due to lack or inactivity of hydrolytic enzymes. Gibberellins are the predominant germination agents found in the phase during the food reserve degradation stage. Cytokinis exert their influence later on the initiation of cell proliferation and expansion. Red light (660mu) promotes and blue specially far-red light (735 mu) inhibits gemination. Dormancy can be broken artificially by various special treatments which may be grouped into two groups.
(A). Physical Treatment
- Heat treatment at 40-45 °C for different duration.
- Low temp. treatment at 2-8 °C for 12-24 hour but seeds should be presoaked for 36 hours before ther are given the low temperature treatment.
- Alternate heating and cooling for several times.
- Alternate drying and wetting for several times.
- Exposure for 24 hours of water soaked seeds to red light for 1-2 hours at 15-25 °C temp.
- Dehusking or removal of seed coats (scarification) by rubbing to make it permeable to water.
(B). Chemicals Treatment
- Inorganic chemicals
(i). By acid treatment: Dilute solutions of HNO3, HCL or H2SO4 (0.1-05%) for different durations in minutes.
(ii). KNO3 (1-3%): Strongest and used for immediate dormancy break after harvesting: NH4NO3 (1-3%), H2O2, H3BO4, etc.
(iii). By gases: By increasing O2 concentration.
- Organic chemicals
(i). Non-hormonal: Thiourea, ascorbic acid.
(ii). Hormonal: GA3 (1-1000 ppm), commonly used hormone to break dormancy; Others are kinetin (1-100 ppm), ethylene (ethrel solution of 100-300).
Objectives of seed treatment
To protect from seed borne and soil borne diseases and insect pests damage.
To promote germination
To hasten nitrogen fixation capacity in case of pulses.
Treatment for diseases and insects control
(a). Physical treatment
(i). Hot water treatment: Seeds are kept on hot water at a certain temp. for certain period.
Later on, after cooling in cold water such seeds are dried in shade. This method is successful in controlling following diseases:
Loose smut of wheat (54 °C for 10 minutes).
Loose smut of barley (54 °C for 13 minutes).
Alternaria blight of wheat (38 °C for 10 minutes)
Leaf spot of til (54 °C for 1 hour).
(ii). Solar treatment: After soaking the seeds in water for some hours, seeds are dried in scorching sun in the month of May-June by keeping on cemented floor or metal sheet. This method is used to control loose smut of wheat and barley.
(b). Chemical treatment: Diferent fungicides e.g., Agrosan G. N., ceresan, captan, thiram etc., are used for the same.
(c). Biological treatment
Seed inoculation inlegumes: Before sowing the legumes crops in the new area, the legume seeds are to be innoculated with rhizobium culture.