Dormancy caused by seed coat impermeability to water and gases can be broken by:

Question

Accepted Answer

The correct option is 2: Scarification

The problem describes a specific type of seed dormancy known as **physical dormancy**, which is caused by a hard, impermeable seed coat that physically prevents the uptake of water and/or oxygen (gases) necessary for the embryo to begin growth. The process designed to mechanically or chemically break this barrier is called **scarification**. The term comes from the action of "scarifying," which means to scratch, cut, or abrade the surface of the seed coat. In nature, this dormancy is often broken by microbial action, passage through an animal's digestive tract, or abrasive rubbing from soil and rocks. In agricultural and horticultural practices, scarification is performed artificially by methods such as rubbing the seeds with sandpaper, nicking the seed coat with a knife, or treating them with strong acid (chemical scarification) or boiling water (heat scarification) to weaken or rupture the tough outer layer. By making the seed coat permeable, the treatment allows water imbibition and gas exchange, thus successfully terminating the physical dormancy and leading to germination.

The incorrect option is 1: Stratification

Stratification is a process of pre-treating seeds with a prolonged period of **cold, moist conditions**, typically achieved by storing them in a refrigerator mixed with a damp medium like sand or peat moss. This treatment is primarily used to break **physiological dormancy**, which is caused by internal chemical inhibitors (like abscisic acid) within the seed embryo. Stratification allows the seed to degrade these inhibitors and synthesize growth promoters, mimicking the natural winter period required by many temperate species. Since the question specifically mentions seed coat impermeability, which is a physical barrier, simply providing cold and moisture (stratification) will not solve the issue of the water being blocked from entering the seed.

The incorrect option is 3: Vernalization

Vernalization is a process where plants are exposed to **low, non-freezing temperatures** over a period to **accelerate or induce flowering**. This response is mainly seen in biennial and winter annual plants, where a cold signal is necessary to complete the transition from vegetative growth to reproductive growth. The primary site of cold perception for vernalization is the apical meristem (shoot tips), not the seed coat. Therefore, while it involves cold treatment, its physiological purpose is entirely different from seed dormancy. Using vernalization to break seed coat impermeability would be ineffective as it addresses the wrong biological mechanism; the cold temperature does not physically alter the hard seed coat.

The incorrect option is 4: Abscisic acid treatment

Abscisic acid (ABA) is a crucial plant hormone that acts as a **growth inhibitor**, and its primary role concerning seeds is to **induce and maintain dormancy** by preventing precocious germination. High levels of ABA are a common cause of internal, or physiological, dormancy. Treating a seed with a high concentration of Abscisic acid would, therefore, be counterproductive to the goal of breaking dormancy. This treatment would either maintain the existing dormant state or induce dormancy in a non-dormant seed, making it the opposite of what is required for germination.