Methods of Breaking Seed Dormancy
Various methods have been used by seed scientist and technologists to break the dormancy of seed.
Simple and widely used methods are
Any treatment i.e. physical or chemical that weakness the seed coat, is known as scarification.
Scarification method is applied, when dormancy is imposed by hard seen coat e. g. in legumes- cajanus cajan, (tur), gram etc.
In this method there are various way to break hard seed coat such as:
Seeds are either rubbed on a sand paper manually. At the time of rubbing care should be taken that not to damage the axis of the seed e.g. Green gram & subabool.
When seed coat is too hard i.e. of woody nature, the seed coat has to be removing completely by breaking it. E.g. Rubber (Havea app) seed India teak wood seed.
Soaking treatment: Soaking hard seed coat in concentrated or diluted solution of sulphuric acid for 1 to 60 minutes, it remove seed coat impermeability. E. g. cotton seeds, India teak wood seeds etc.
B. Temperature Treatments:
When the dormancy is due to embryo factor i.e. the seed is incubating at low temp. (0- 5o C) over a substratum for 3 to 10 days placing it at optimum temp. Required for germination. E.g. mustard. – (Brassica campestrits)
Some seeds required a brief period of incubation (from a few hours to one to five days) at 40 to 50 oC before germinating at required temp. ( in this method care should be taken that moisture content of the seed is not more than 15% e.g. paddy (Oryza Sativa)
Hot water treatment is also an effective method of breaking hard- seed ness in legumes. In this method the seeds are soaked in water at 80oC temp. For 1 – 5 minutes (depending up on the type of seed) before putting for germination.
C. Light Treatments:
Same seeds do not germinate in dark thus it provides continuous or periodic exposure of light is essential e. g. Lettuce (Lactuca Sativa) required red light (660nm) or white light is essential for germination to occur.
D. Treatments with growth regulators & other Chemicals:
Endogenous dormancy may be due to presence of germination inhibitors. Application of low level of growth regulators (i.e. Gibberellins, Cytokinins and Ethylene etc) may break the seed dormancy.
Most widely used growth regulators are gibberellins and kinetics e.g. seeds of sorghum crop presoaking seed treatment with GA3 at the conc. Of 100 ppm have been used for breaking seed dormancy
Among other chemicals potassium nitrate (0.2%) and thio – urea (0.5 to 3%) are widely used for breaking seed dormancy in oat (Avena Sativa), barley (Hordeum vulgare), tomato (Lycopersicon spp).
(For prepare 100 ppm solution of GA3, weigh 100 mg of GA3 & dissolve in a few drops of alcohol and make up the final volume (1000 ml) by adding distilled water).
(50 ppm kinetin 5 mg dissolved in few drops of alkaline made with sodium hydroxide and makes the final volume 100ml it gives to final conc. Of 50 ppm)