The Pedaliaceae comprise about 60 species of herbaceous plants within 16 genera and are closely related to Scrophulariaceae and Martyniaceae. Two species are cultivated for their edible (oily) seeds, viz: Sesamum indicum L., sesame; and Ceratotheca sesamoides Endl. The fruits are either capsules or hard indehiscent nuts. Seed storage behaviour is orthodox.
SEED DORMANCY AND GERMINATION
The seeds are non-endospermic, possess linear embryos and flattened cotyledons, and can be dormant. Part of the problems associated with germination tests are caused by the seed coat. Seed coat removal and treatment of the seeds with gibberellins tends to promote germination.
Detailed information is provided for the genus Sesamum in this chapter. For developing suitable techniques for other species, RBG Kew Wakehurst Place suggests, as a first step, testing seeds at a constant temperature of 26°C with light applied for 12h/d (but see comment for Sesamum). If this does not lead to satisfactory germination then experiment with further treatments. Clues to suitable further treatments can be obtained from the information provided for Sesamum in this chapter.
SESAMUM
|
S. indicum L. [S. orientale L.] |
sesame, simsim, beniseed, gingelly, till |
I. Evidence of dormancy
Sesame seeds may exhibit dormancy (1-4). Six months after-ripening results in loss of dormancy (1). The position of capsules on the plant and the degree of maturity affect dormancy (4). Seeds from wild collections tend to show deeper dormancy (3), apparently failing to germinate due to impermeable seed coats (3).
II. Germination regimes for non-dormant seeds
TP: 20°/30°C (16h/8h): 6d (AOSA,ISTA)
III. Unsuccessful dormancy-breaking treatments
Indolebutyric acid: co-applied, 100 ppm, at 26°C in light, 16h (2); co-applied, 500 ppm, at 26°C in light, continuous or 16h, or dark (2)
Coumarin: co-applied, 500 ppm (2)
IV. Partly-successful dormancy-breaking treatments
Pre-soak: 48h (1)
GA3: pre-applied, 48h, 1000 ppm (1); co-applied, 0.5-500 ppm, at 26°C in light, 16h (2)
Indolebutyric acid: co-applied, 0.5-50 ppm, at 26°C in light, 16h (2); co-applied, 100 ppm, in light, continuous, or dark (2)
Coumarin: co-applied, 0.5-100 ppm, at 26°C in light, 16h (2) 2,4-Dichlorophenoxyacetic acid: co-applied, 0.5-10, 100, 500 ppm, at 26°C in light, 16h (2)
V. Successful dormancy-breaking treatments
GA3: pre-applied, 48h, 100-500 ppm (1); co-applied, 0.5-500 ppm, at 26°C in light, continuous, or dark (2)
Indolebutyric acid: co-applied, 0.5-50 ppm, at 26°C in light, continuous, or dark (2)
Coumarin: co-applied, 0.5-100 ppm, at 26°C in light, continuous, or dark (2)
2,4-Dichlorophenoxyacetic acid: co-applied, 0.5-500 ppm, at 26°C in light, continuous, or dark (2)
VI. Comment
The observation that continuous light or continuous dark are both more promotory than a single 16 hour light treatment (2) is surprising. Nevertheless the implication for gene banks is clear: sesame seeds should be tested for germination in the dark. An alternating temperature regime of 20°/30°C (16h/8h) as prescribed by ISTA/AOSA is satisfactory for non-dormant fresh and aged seeds (A), but a further stimulus is required for dormant seeds. Of the four successful dormancy-breaking agents listed above gibberellic acid is the most satisfactory - since it promotes germination over the widest range of conditions (2). Pre-application - 48 hours, 500 ppm is suggested - may be preferable to co-application - 10, or possibly, 50, ppm is suggested - since considerable promotion of germination is provided by pre-soak treatments alone (2).
VII. References
1. Ashri, A. and Palevitch, D. (1979). Seed dormancy in sesame (S. indicum) and the effect of gibberellic acid. Experimental Agriculture, 15, 81-83.
2. Chatterji, U.N., Sankhla, N. and Baxi, D. (1966). Preliminary studies on the effects of certain growth substances on germination of Sesamum indicum Linn. seeds. Indian Agriculturists, 10, 46-56.
3. Richharia, R.H. and Dhodapkar, D.R. (1940). Delayed germination in sesame, Sesamum indicum. Indian Journal of Agricultural Science 10, 93-95.
4. Sheelavantar, M.N., Ramanagouda, P. and Krishnamurthy, K. (1974). Causes for low germination in sesamum variety C-50. Current Research, 3, 89-90.
