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Literature review
They compared the activity of this synthesized butenolide with that of smoke water
dilutions and found a high similarity in the germination delivered by these two
compounds. Since this study, many experiments have been conducted using
butenolide. This compound has been shown to enhance germination in a similar way
to smoke water dilutions in many genera including Acacia, Eucomis and Dioscorea
(KULKARNI et al., 2006b; KULKARNI et al., 2006a; KULKARNI et al., 2007). In these
experiments a 10 −7 M butenolide solution was used.
2.8.5 Phytochromes and light quality
Photo-sensitive substances that are responsible for photoperiodic control of
germination, in some species, were first discovered in 1959 (COPELAND, 1976).
There are two photo-reversible forms of phytochrome in plants (COPELAND, 1976).
The first is PR phytochrome, which is sensitive to orange-red light (600-680 nm), and
the second is PF-R phytochrome, which is sensitive to far-red light (700-760 nm). In
most species the greatest promotion of germination occur after exposure to light in
the red area (660 to 700 nm) with a peak of germination often being observed at 670
nm (COPELAND, 1976). Wavelengths at 440 nm, above 700 nm and below 290 nm
are known to inhibit germination. No studies has shown an effect of wavelengths of
290 to 400 nm on germination (COPELAND, 1976)
2.8.6 Scarification
Mechanical scarification
To mechanically scarify seeds a small hole is made in the seed coat using a needle
or a scalpel or the whole seed coat is scarified with sandpaper or specialized
equipment (BASKIN & BASKIN, 1998).
Acid scarification
This is usually done by soaking seeds in concentrated sulphuric acid for a short
period of time after which they are rinsed several times with distilled water (BASKIN
& BASKIN, 1998). By using acid scarification, both the testa and the seed pores are
scarified (BASKIN & BASKIN, 1998).
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