**4.1 Scarification**

Scarification is a technique used to break mechanical dormancy [75] which acts by impeding the perception of germination elicitors like water, light, temperature and

*Seed Dormancy: Induction, Maintenance and Seed Technology Approaches to Break Dormancy DOI: http://dx.doi.org/10.5772/intechopen.106153*

oxygen by the embryo. Scarification techniques used commonly include; mechanical, thermal, hot water and chemical scarification. This type of dormancy breaking has been documented in a number of families e.g. *Anacardiaceae*, *Arecaceae*, *Cornaceae*, *Elaeagnaceae*, *Empeteaceae*, *Juglandaceae*, *Meliaceae*, *Nyssaceae*, *Oleaceae*, *Rhamnaceae*, *Rosaceae* and *Santalaceae* [76].

#### *4.1.1 Mechanical scarification*

This method can be accomplished, by abrading the surface of the seed until the endosperm becomes visible, or by using a knife to scrap out the hair plug at the micropylar opening. This method gives the possibilities to bring the best of germination capacity of seeds, although its application is difficult for significant quantities of seeds. Mechanical scarification accelerates germination and some chemical treatments significantly increased germination speed of the mechanically scarified seeds [77].

#### *4.1.2 Thermal scarification*

Thermal scarification can be by dry heat or hot water on the other hand can be realized by subjecting seeds under a high and steady temperature of a given duration. In the case of oil palm, dormancy is only broken when seeds are exposed to a constant thermal scarification temperature of 40°C for 80 days [78].

#### *4.1.3 Hot water treatment*

This treatment involves soaking seeds in water at 40–100°C depending on the species and seed coat thickness, for a specific period of time or until the boiling water cools to room temperature [79]. A brief soak in 80°C water for 10 minute resulted to 91.26% germination of *Acacia catechu* while soaking in 100°C water for a period of 12min for *Elaeocarpus floribundus* gave 84% seed germination success rates [80]. Improvement of germination via soaking in hot water could be associated to weakening of seed coat. Such weakening probably occurs because lignins and pectins present on epidermal layer of the seed coat are dissolved, hence water and oxygen signals are perceived by the embryo [81].

#### *4.1.4 Acid scarification*

This method is recommended only for those seeds that are very hard to germinate, as damage to the embryo during the process can be high [82]. The treatment generally requires soaking seeds in 95% pure (1.84 specific gravity) sulfuric acid. The soaking duration is a factor of the degree of thickness of the pericarp of a given species. Once the soaking time elapses, acid is decanted, then seeds washed severally and dried [83]. The timing of this treatment is critical therefore the soaking period and the post soak washing have to be precisely controlled to avoid seed injury. The acid scarification can be applied either at room temperature or in a heated condition by soaking the seed in different concentrations of sulfuric acid for 10–30 min [79].

#### **4.2 Alternating soaking and drying in water**

This is the simplest treatment to give the seeds an early start in the germination process. It is also known as invigoration and its effects are not only on the activation of enzymes and mobilization of reserves in the aleorone layer [84], but also on the softening of hard seed coats and leaching out of chemical inhibitors. Aerated, coldwater soaking for 28 days at 11°C was found to be effective in breaking moderate dormancy and enhancing germination of *Pinus taeda* seeds [85]. Soaking and drying treatments can have varying effects on germination depending on the rate of drying, the species tested, and the duration of the soaking [86].
