The Piperaceae comprise over 1000 species of herbaceous plants, shrubs and sometimes climbers and trees some of which provide condiments (e.g. Piper nigrum L., pepper). The fruits are dry or fleshy small indehiscent berries and seed storage behaviour is orthodox (though longevity may be comparatively short).
SEED DORMANCY AND GERMINATION
The seeds are small with a minute embryo, copious perisperm and little endosperm. They may be dormant. Treatments to the seed coat and alternating temperatures may promote germination, but careful regulation of the light environment may be necessary for germination to occur (see Chapter 6, Volume I). Detailed information is provided for the genus Piper in this chapter.
PIPER
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P. auritum HBK |
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P. hispidum Sw. |
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P. nigrum L. |
pepper |
I. Evidence of dormancy
Evidence of dormancy in seeds of P. nigrum is not great. In nursery cultivation seeds germinate satisfactorily provided they are sown shallow (2), or on top of sand (3), or in the shade (1,3,4). Dormancy may be present in some lots, however, because the germination of over-ripe seeds is reported to be greater than the germination of less mature seeds (3).
Considerable dormancy can be exhibited in seeds of P. auritum and P. hispidum (2,6,7). For example, seeds of P. hispidum maintain imbibed at 25°C in the dark faíled to germinate within a year, but were subsequently capable of germinating if provided with sufficient stimulus (7).
II. Germination regimes for non-dormant seeds
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III. Unsuccessful dormancy-breaking treatments
P. auritum
Light: far red, 5 lux, at 25°C (6); dark, at 25°C (6)
P. hispidum
Light: dark, at 25°C (2,7); far red, 10 min (2,7); red, less than 20 min (7); red, 10 min/12h (7)
IV. Partly-successful dormancy-breaking treatments
P. hispidum
Light: red, 30-120 min, at 25°C (7); red, 10 min/6h, 10 min/8h (7)
V. Successful dormancy-breaking treatments
P. auritum
Light: red, low (immeasurable), at 25°C (6); white, 12h/d, at 25°C (6)
P. hispidum
Light: white, 12h/d, at 25°C (2,7); red, 6h, at 25°C (7); red, 2h/12h, 2h/8h, at 25°C (7); blue, at 25°C (2)
P. nigrum
Scarification: concentrated sulphuric acid, 2 min, low light (4)
VI. Comment
The above provides ample evidence that the quality and dosage of light received by seeds of Piper spp. markedly influences germination. Incidentally the indirect evidence summarised from observations of nursery bed sowings (1,3-5) emphasises that recommendations on the light environment should accompany samples of accessions destined for field sowings.
On the basis of the limited evidence presently available, it is suggested that seeds of Piper spp. be tested for germination at 25°C with red light applied, either for 2 hours in every 8-12 hours (7), or as recommended in Chapter 6. It is suggested that gene banks might investigate the response of seed germination to alternating temperatures - in a stimulatory light environment - in order to determine whether more suitable germination test regimes can be devised - particularly since alternating temperatures may be beneficial in increasing the permeability of seed coats, which are reported to be impermeable in P. nigrum (4).
VII. References
1. De Waard, P.W.F. and Zeven, A.C. (1969). Pepper. In Outline of perennial crops breeding in the tropics (eds. F.P. Ferwerda and F. Wit), pp. 409-426, Veenman and Zonen, Wageningen.
2. Ludlow Wiechers, B. and Vázquez-Yanes, C. (1976). [Germination of seeds of Piper hispidum under different light conditions.] In Investigaciones sobre la regeneracion de selvas altas en Vera Cruz, Mexico, pp. 263-278, Compania Editorial Continental, S.A.
3. Nuryani, Y. (1978). [Germination of black pepper seeds.] Pemberitaan, 31, 33-40.
4. Purseglove, J.W. (1968). Tropical Crops. Dicotyledons. Longman, London.
5. Singh, H.B. et al (1974). Black pepper (Piper nigrum). In Handbook of Plant Introduction in Tropical Crops, pp. 126-127. Plant Production and Protection Division, FAO, Rome.
6. Vázquez-Yanes, C. (1980). Light quality and seed germination in Cecropia obtusifolia and Piper auritum from a tropical rain forest in Mexico. Phyton, 38, 33-35.
7. Vázquez-Yanes, C. and Orozco-Segovia, A. (1982). Germination of the seeds of a tropical rain forest shrub, Piper hispidum Sw. (Piperaceae), under different light qualities. Phyton, 42, 143-149.
