The Amaranthaceae comprise about 500 species within 40 genera. The most important genus is Amaranthus which is cultivated for grain and as a leaf vegetable. The seeds show orthodox storage behaviour.
SEED DORMANCY AND GERMINATION
The fruits are usually surrounded by a persistent perianth. B.R. Atwater classifies seed morphology as endospermic seeds with peripheral linear embryos (see Table 17.1, Chapter 17). Light, alternating temperatures, pre-washing and removal of the seed covering structures can promote germination, but some care may be required in defining promotory treatments in detail. Detailed information on seed germination is provided for the genera Amaranthus and Celosia in this chapter. A limited number of other recommended germination test procedures is provided in Table 20.1 and the algorithm below may be helpful in developing suitable germination test procedures.
RBG Kew Wakehurst Place algorithm
The first step of the algorithm is to test three samples of the seeds at constant temperatures of 26°C, 31°C, and 36°C with light applied for 12h/d. If full germination has not been promoted and there is a trend in germination response to constant temperatures, then test further samples of seeds at more extreme constant temperatures. That is: if germination was greatest at 26°C then test at constant temperatures of 16°C and 21°C with light applied for 12h/d; but if germination was greatest at 36°C then test at a constant temperature of 41°C with light applied for 12h/d. If, however, germination was greatest at 31°C then go to the next step of the algorithm.
If full germination has not been promoted, the second step of the algorithm is to test a further sample of seeds in an alternating temperature regime of 33°/19°C (12h/12h) with light applied for 12h/d during the period spent at the upper temperature.
If full germination has not been promoted, the third step of the algorithm is to estimate viability using a tetrazolium test (see Chapter 11, Volume I).
If the result of the tetrazolium test indicates that the failure to achieve full germination is due to the presence of dead seeds and that one of the above regimes promoted the germination of all, or almost all, the viable seeds, then this regime is used for all subsequent germination tests. If, however, the result of the tetrazolium test indicates that dormancy has not been broken by the regimes applied so far in the algorithm, then experiment with modifications to the above regimes. Clues to possible satisfactory dormancy-breaking treatments and promotory germination test environments can be obtained from the information provided in this chapter for the genera Amaranthus and Celosia and from Table 20.1.
TABLE 20.1 Summary of germination test recommendations for species within the Amaranthaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Gomphrena globosa L. |
TP; BP |
20°/30°C; 20°C |
14d |
Potassium nitrate |
ISTA |
|
TP |
20°/30°C |
14d |
light, potassium nitrate |
AOSA |
|
|
|
20°/30°C' |
10d |
Light |
Atwater |
AMARANTHUS
|
A. albus L. |
tumble pigweed |
|
A. blitoides Wats. |
prostrate pigweed |
|
A. caudatus L. [A. paniculatus L.; A.
cruentis L.] |
grain amaranth, pigweed, love-lies-bleeding, tassel
flower |
|
A. graecizans L. |
tumbleweed, prostrate pigweed |
|
A. hybridus L. |
edible amaranth, smooth pigweed |
|
A. hypochondriacus L. |
|
|
A. lividus L. |
|
|
A. palmeri Wats. |
Palmer amaranth |
|
A. powellii Wats. |
Powell's pigweed |
|
A. retroflexus L. |
green amaranth, redroot pigweed |
|
A. spinosus L. |
spiny amaranth |
|
A. tricolor L. |
|
I. Evidence of dor mancy
Almost without exception seeds of Amaranthus spp. show considerable dormancy. This is possibly because the majority of references cited here concern seeds from weedy plants of Amaranthus spp. Only in a minority of papers has the dormancy of seeds from cultivated plants within the genus Amaranthus been investigated. Nevertheless it is clear that dormancy can also be considerable in seeds from cultivated plants - e.g. (16).
After-ripening treatment periods required to remove dormancy from the majority of seeds can be considerable: 180 days (4,22), 300 days (20) or as many as 4 years (28) for seeds of A. retroflexus; and 6 months for seeds of A. blitoides and A. graecizans (22).
II. Germination regimes for non-dormant seeds
A. caudatus, A. hybridus, A. hypochondriacus
TP: 20°/30°C (16h/8h); 20°C: 14d (ISTA)
A. retroflexus
Constant temperatures: 21°-42°C, 5d (8); 25°C in light, 12h/d, 2.3 x 10-3 W cm-2 (5); 35°C in light, 10d (9)
Amaranthus spp.
TP: 20°/30°C (16h/8h): 8d (AOSA)
Alternating temperatures: 20°/30°C (16h/8h) in light, 10d (1)
III. Unsuccessful dormancy-breaking treatments
A. albus
Constant temperatures: 29°-38°C (26)
Alternating temperatures: 20°/32°C, 22°/43°C (12h/12h) (26)
Potassium nitrate: co-applied, 1%, at 20°/30°C (12h/12h) (26)
Acetone: pre-applied, 1-20 min, germinate at 20°/30°C (12h/12h) (26)
Sodium hypochlorite: pre-applied, 1-5 min, germinate at 20°/30°C (12h/12h) (26)
Scarification: concentrated sulphuric acid, 4,8 min, germinate at 20°/30°C (12h/12h) (26)
Catechol: co-applied, 10-4-10-2 M, at 30°C in dark (13)
Pyrogallol: co-applied, 10-4, 10-3-10-2 M, at 30°C in dark (13)
Hydroxylamine hydrochloride: co-applied, 10-5, 5x10-5, 5x10-3 M, at 30°C in dark (13)
A. blitoides
Constant temperatures: 24°-30°C in light, 125 fc, or dark (17); 42°-44°C in dark (17); 25°C (22)
Pre-chill: 5°C, 6m (22)
A. caudatus
Constant temperatures: 40°C (19)
Pre-soak: (25)
Sodium azide: pre-applied, 10-3 M (25)
Ammonium hydroxide: pre-applied, 10-3 M (25)
Light: white, 2100 ergs cm-2 s-1, at 10°-20°C (19)
A. graecizans
Constant temperatures: 15°C, 20°C (22)
Alternating temperatures: 15°/28°C in light or dark (10)
Pre-chill: 5°C, 6m (22)
Potassium nitrate: co-applied, 0.125-1%, at 20°/30°C (12h/12h) (26)
Sodium hypochlorite: pre-applied, 1-20 min, germinate at 20°/30°C (12h/12h) (26)
Acetone: pre-applied, 1-20 min, germinate at 20°/30°C (12h/12h) (26)
Scarification: concentrated sulphuric acid, 2,8 min, germinate at 20°/30°C (12h/12h) (26)
A. hybridus
Constant temperatures: 29°-38°C (26)
Alternating temperatures: 15°/28°C in light or dark (10); 15°/13°C, 20°/15°C (day/night) in light, 15d (16); 19°/23°C, 20°/32°C, 22°/43°C (12h/12h) (26)
Potassium nitrate: co-applied, 0.125-1%, at 20°/30°C (12h/12h) (26)
Sodium hypochlorite: pre-applied, 1-5 min, germinate at 20°/30°C (12h/12h) (26)
Scarification: concentrated sulphuric acid, 2,4,8 min, germinate at 20°/30°C (12h/12h) (26)
A. palmeri
Constant temperatures: 29°-38°C (26)
Alternating temperatures: 19°/23°C, 20°/32°C, 22°/43°C (12h/12h) (26)
Potassium nitrate: co-applied, 0.125-1%, at 20°/30°C (12h/12h) (26)
Acetone: pre-applied, 2,20 min, germinate at 20°/30°C (12h/12h) (26)
Scarification: concentrated sulphuric acid, 2-8 min, germinate at 20°/30°C (12h/12h) (26)
A. retroflexus
Constant temperatures: 15°C in light, 12h/d, 2.3x10-3 W cm-2 (5); 15°-30°C, dark, 7d (28); 20°C (2,3,4); 20°C, 25°C, 30°C, dark or light, red, 5 min after 3d (35); 25°C, 30°C, 14d, dark (6); 29°-38°C (26); 30°C, dark (21); 30°C (31)
Alternating temperatures: 19°/23°C, 20°/32°C, 22°/43°C (12h/12h) (26)
Pre-chill: 5°C, 6m (22)
Warm stratification: 15°C, germinate at 35°C, both in light, 12h/d, 2.3x10-3 W cm-2 (5); 20°C, 35°C, 3d, dark, then 20°-30°C, dark (35)
Abscisic acid: co-applied, 10-4M, at 23°C in dark (15)
Potassium nitrate: co-applied, 0.125-1%, at 20°/30°C (12h/12h) (26)
Acetone: pre-applied, 1-20 min, germinate at 20°/30°C (12h/12h) (26)
Sodium hypochlorite: pre-applied, 1-20 min, germinate at 20°/30°C (12h/12h) (26)
Scarification: concentrated sulphuric acid, 4,8 min, germinate at 20°/30°C (12h/12h) (26)
A. spinosus
Constant temperatures: 29°-38°C (26)
Alternating temperatures: 19°/23°C, 20°/32°C, 22°/43°C (12h/12h) (26)
Potassium nitrate: co-applied, 0.125-1%, at 20°/30°C (12h/12h) (26)
Acetone: pre-applied, 1-20 min, germinate at 20°/30°C (12h/12h) (26)
Sodium hypochlorite: pre-applied, 1-20 min, germinate at 20°/30°C (12h/12h) (26)
Scarification: concentrated sulphuric acid, 4,8 min, germinate at 20°/30°C (12h/12h) (26)
IV. Partly-successful dormancy-breaking treatments
A. albus
Alternating temperatures: 19°/23°C (12h/12h) (26); 20°/30°C, 20°/35°C (16h/8h) in dark (14)
Light: red, 5 min, 1.9x10-4 W cm-2, after 24h dark (34)
Ethylene: co-applied, 1-100 ppm, at 30°C in dark (34); co-applied, 1, 10 ppm, at 30°C in red light, 5 min, 1.9x10-4 W cm-2, after 24h dark (34)
Potassium nitrate: co-applied, 10-2 M, at 30°C in dark (12); co-applied, 0.125-0.5%, at 20°/30°C (12h/12h) (26)
Sodium nitrite: co-applied, 10-3 M, at 30°C in dark (12)
Ammonium chloride: co-applied, 10-2 M, at 30°C in dark (12)
Potassium cyanide: co-applied, 10-4 M, at 30°C in dark (12)
Potassium azide: co-applied, 10-5 M, at 30°C in dark (12)
Pyrogallol: co-applied, 3x10-4 M, at 30°C in dark (13)
Hydroxylamine hydrochloride: co-applied, 10-4-10-3 M, at 30°C in dark (13)
Thiourea: co-applied, 10-3-10-2 M, at 30°C in dark (13)
Sodium hypochlorite: pre-applied, 20 min, germinate at 20°/30°C (12h/12h) (26)
Scarification: concentrated sulphuric acid, 2 min, germinate at 20°/30°C (12h/12h) (26)
A. blitoides
Constant temperatures: 30°-37°C in dark (17); 40°-44°C in light, continuous, 125 fc, or dark (17)
Warm stratification: 14°C, 6m (22)
Removal of seed covering structures: then germinate at 25°C (22)
A. caudatus
GA3: co-applied, 10-100 mg/l (19)
Thiourea: co-applied, 0.25%, at 27°C in light (23)
Potassium cyanide: pre-applied, 10-3 M (25)
A. graecizans
Constant temperatures: 25°-35°C (22)
Warm stratification: 14°C, 6m (22)
Removal of seed covering structures: then germinate at 15°-35°C (22)
Scarification: concentrated sulphuric acid, 4 min, germinate at 20°/30°C (12h/12h) (26)
A. hybridus
Alternating temperatures: 30°/25°C (day/night) in light, 15d (16); 20°/15°C (day/night) in dark, 15d (16); 15°/13°C (day/night) in dark, 15d (16); 25°/20°C (day/night) in light or dark, 15d (16)
Light: dark, at 25°/20°C, 20°/15°C (day/night), 15d (16); 2h, after 60-150h imbibition in dark (7)
Potassium nitrate: co-applied, 0.2%, at 24°C (7)
Acetone: pre-applied, 1-20 min, germinate at 20°/30°C (12h/12h) (26)
Sodium hypochlorite: pre-applied, 20 min, germinate at 20°/30°C (12h/12h) (26)
A. lividus
Alternating temperatures: 20°/30°C (32)
A. palmeri
Acetone: pre-applied, 1 min, germinate at 20°/30°C (12h/12h) (26)
Sodium hypochlorite; pre-applied, 1-20 min, germinate at 20°/30°C (12h/12h) (26)
A. powellii
Alternating temperatures: 30°/18°C, light/dark (day/night), 100d (11)
A. retroflexus
Constant temperatures: 25°-28°C (35); 30°C (3,4); 35°C (31); 35°C, dark (6); 35°C, 40°C, dark, 7d (28)
Alternating temperatures: 23°/35°C (12h/12h) (31); 25°/8°C (18h/6h) (24)
Pre-chill: 5°C, 3d, germinate at 30°C in dark (20,21); 5°-20°C, 3-15d, germinate at 35°C (35)
Warm stratification: 14°C, 6m (22); 15°C, 7d, germinate at 30°C (30); 25°C, 8-31d, germinate at 35°C (30); 40°C, dark, 1,5d, germinate at 35°C, dark (29)
Light: dark (24); white, 2x10-5, 3x10-5 mol m-2 s-1, 1,5d, at 35°C (29); fluorescent, 5x10-5 mol m-2 s-1, at 30°C, 35°C (28); fluorescent, 5 min, 4x103 ergs cm-2 s-1, after 24h imbibition at 30°C in dark, germinate at 30°C in dark (20); red, 5 min (4); red, 6x10-4 W cm-2, 5 min, after 3d at 35°C in dark, germinate at 35°C in dark (33); red, 1.5x10-11-1.7x10-9 mol cm-2 s-1, after 24-140h in dark at 35°C (36); red, 3.5x10-10-1.4x10-9 mol cm-2 s-1, after 96h in dark at 35°C (36)
Ethylene: co-applied, 0.00001-0.1%, at 30°C in dark (6); co-applied, 1-100 ppm, at 30°C in dark, 7d (28); co-applied, 0.001%, at 35°C in light, continuous, 2x10-5-3x10-5 mol m-2 s-1 (29); co-applied, 0.001%, at 35°C in dark (29); co-applied, 0.51, 51 cm3 m-3, at 30°C, after 8-31d at 30°C (30); co-applied, 0.51 cm3 m-3, at 35°C, after 8-31d at 25°C (30); co-applied, 51 cm3 m-3, at 35°C, after 8,16d at 25°C (30); co-applied, 0.05-51 cm3 m-3, at 23°/35°C (12h/12h) (31); co-applied, 1, 10 ppm, at 30°C in dark or red light, 5 min, 1.9x10-4 W cm-2, after 24h dark (34)
GA3: co-applied, 2.6x10-5 M, at 30°C (3); co-applied, 2.6x10-5 M (4)
Scarification: abrasive sand, 4-9w (8); concentrated sulphuric acid, 2-3 min (8); concentrated sulphuric acid, 2 min, germinate at 20°/30°C (12h/12h) (26)
Ultrasonics: 20 kc/s, 1 min, germinate at 23°C in dark (15) 2-Chloroethyl phosphonic acid: co-applied, 10 ppm, at 23°C in dark (15)
Napthaleneacetic acid: co-applied, 10-6 M, at 23°C in dark (15)
A. spinosus
Light: red, 5 min, 1.9x10-4 W cm-2, after 24h dark (34)
Ethylene: co-applied, 1-100 ppm, at 30°C, in dark or red light, 5 min, 1.9x10-4 W cm-2, after 24h dark (34)
Scarification: concentrated sulphuric acid, 2 min, germinate at 20°/30°C (12h/12h) (26)
A. tricolor
Constant temperatures: 30°C in light (27)
V. Successful dormancy-breaking treatments
A. albus
Ethylene: co-applied, 100 ppm, at 30°C in red light, 5 min, 1.9x10-4 W cm-2, after 24h dark (34)
Hydroxylamine hydrochloride: co-applied, 3.2x10-3 M, at 30°C in dark (12)
A. blitoides
Constant temperatures: 30°-37°C in continuous light, 125 fc (17); 30°-37°C, 48h dark, then light, 5 min, 125 fc, then dark (17)
A. caudatus
Pre-chill, Potassium nitrate (ISTA)
Constant temperatures: 10°-40°C, dark (19); 25°-40°C in white light, 2100 ergs cm-2 s-1 (19)
Alternating temperatures: 15°/28°C in light (10)
A. hybridus, A. hypochondriacus
Pre-chill, Potassium nitrate (ISTA)
A. powellii
Alternating temperatures: 30°/18°C (day/night) in dark, 7d, then light/dark (day/night), 34d (11)
A. retroflexus
Constant temperatures: 35°C (2)
Alternating temperatures: 30°/18°C, light/dark (day/night), 100d (11); 30°/18°C (day/night) in dark, 7d, then light/dark (day/night), 34d (11)
Warm stratification: 20°C, 35°C, 3d, dark, then red light, 5 min, then 35°C in dark (35); 25°C, 4d, dark, then 35°C in light, continuous, 2x10-5-3x10-5 mol m-2 s-1, with ethylene, co-applied, 0.001% (29)
Light: red, 6x10-4 W cm-2, 5 min, after 24h at 35°C in dark, germinate at 35°C in dark (33); red, 2.8x10-9, 4x10-9, 5.6x10-9 mol cm-2 s-1, after 96h at 35°C in dark (36)
Pre-dry: 3h-3d (2)
Ethylene: co-applied, 51 cm3 m-3 at 35°C, after 24,31d at 25°C (30); co-applied, 51 cm3 m-3 at 40°C, after 7d at 25°C, 30°C (30); co-applied, 100 ppm, at 30°C in dark or red light, 5 min, 1.9x10-4 W cm-2, after 24h dark (34)
GA3: co-applied, 10-2 M, at 23°C, dark (15)
Thiourea: co-applied, 10-2 M, at 23°C, dark (15)
Pre-soak: 40°C, 2h, germinate at 23°C, dark (15)
Amaranthus spp.
Light (AOSA)
VI. Comment
Comparatively few treatments have been reported which are able to break the dormancy of all seeds within accessions of Amaranthus spp. Light is a factor of critical importance. At first sight the literature may appear confusing, since the effect of light on germination has been reported as both stimulatory (2,4,7,11,17,18,29,32,33) and inhibitory (16,19,24). Inhibitory action occurs when the light is of the wrong wavelength - for example, far red (19) - or the dosage is too high. To obtain the maximum promotion from light additional parameters are important: these include temperature, the timing of the light application, and - more occasionally - the presence of other dormancy-breaking agents.
At constant temperatures, high temperatures are required for the germination of dormant seeds: above 30°C (18), 30°-37°C (17), 35°C (22), 35°-40°C (28), or 40°C (14). Alternating temperatures can promote germination: 20°/35°C (16h/8h) is reported to be superior to 20°/30°C (16h/8h) - the AOSA prescribed regime - whilst both are better than high constant temperatures (14); 30°/25°C (day/night) is superior to 25°/20°C, 20°/15°C, or 15°/30°C (day/night) (16); 25°/8°C (18h/6h) is reported to be better than constant temperatures between 25° and 28°C (24); and 23°/35°C (12h/12h) is superior to constant temperatures of 30°C or 35°C (31), but to obtain maximum promotion the initial imbibition temperature should be 23°C, not 35°C - that is 23°/35°C, not 35°/23°C (31). However, neither constant nor alternating temperatures alone can be regarded as satisfactory. For example, testing dormant seeds from five Amaranthus spp. at constant temperatures between 29°C and 38°C, or alternating temperatures of 19°/23°C, 20°/32°C or 22°/43°C in the dark resulted in no more than 10% germination in any one environment, with no significant difference in germination between the various germination test regimes (26).
At high constant temperatures the germination of dormant seeds is promoted by only a very short duration light treatment, for example in A. blitoides (17) and A. retroflexus (18). As little as 45-60 seconds can be sufficient to promote the germination of the majority of dormant seeds - for example, promoting germination from 25% to 92% (17). However, the timing of the light treatment in relation to the start of imbibition is critical: in A. hybridus the maximum promotion is reported after 80-150 hours (7); in A. blitoides after 48 hours (17); and in A. retroflexus after 96 hours (36). Moreover, the response to light can be considerably increased in the presence of other dormancy-breaking agents - particularly potassium nitrate (7). Although the above times appear to vary - probably due to differences of irradiance reaching the seeds (36) - once the maximum sensitivity to light has been achieved during imbibition, delaying the light treatment does not reduce the germination of seeds of Amaranthus spp. (7,18).
Given the wide differences in the level of seed dormancy between accessions within the genus Amaranthus it is difficult to make precise recommendations. Nevertheless, the following regime is tentatively suggested: imbibe seeds in the dark at 35°C for four days with 0.2% potassium nitrate co-applied; expose briefly to red light - 1x10-9 mol cm-2 is probably sufficient (36). Although one exposure is probably satisfactory, it might be worthwhile to provide this daily in case some individual seeds require a longer period of imbibition before they reach maximum sensitivity to light. It is likely that an alternating temperature regime would be preferable to a constant temperature of 35°C; 20°-25°/35°C (12h/12h) is suggested, again with potassium nitrate and red light as described above, but this must be regarded as untested as yet. Finally, if it is difficult to provide a suitable light environment it is worth noting that pre-chill treatments can reduce the need for light in subsequent germination tests (35); try 14 days at 3°-5°C and then transfer to 35°C in the dark for the germination test.
VII. References
1. Atwater, B.R. (1980). Germination, dormancy and morphology of the seeds of herbaceous ornamental plants. Seed Science and Technology, 8, 523-573.
2. Barton, L.V. (1962). The germination of wed seeds. Weeds, 10, 174-182.
3. Chadoeuf-Hannel, R. and Barralis, G. (1982). Comportement germinatif des graines d'Amaranthus retroflexus L. récoltées dans les conditions naturelles. Weed Research, 22, 361-369.
4. Chadoeuf-Hannel, R. and Barralis, G. (1983). Evolution de l'aptitude à germer des graines d'Amaranthus retroflexus L. récoltées dans différentes conditions, au cours de leur conservation. Weed Research, 23, 109-117.
5. Chakrabarti, A.G. (1977). Effects of temperature shift on weed seed germination. Castanea, 42, 279-285.
6. Egley, G.H. (1980). Stimulation of common cocklebur (Xanthium pensylvanicum) and redroot pigweed (Amaranthus retroflexus) seed germination by injections of ethylene into soil. Journal for Weed Science, 28, 510-514.
7. Engelhardt, M., Vicente, M. and Silberschmindt, K. (1962). Ação da luz e do nitrato de potàssio sôbre a germinacao de sementes de "Amarantus hybridus" L. Revista Brasileira Biologia, 22, 1-7.
8. Evans, C.R. (1922). Effect of temperature on germination of Amaranthus retroflexus. Botanical Gazette, 73, 213-225.
9. Everson, L. (1949). Preliminary studies to establish laboratory methods for the germination of weed seed. Proceedings of the Association of Official Seed Analysts, 39, 84-89.
10. Fenner, M. (1980). Germination tests on thirty-two East African weed species. Weed Research, 20, 135-138.
11. Frost, R.A. and Cavers, P.B. (1975). The ecology of pigweeds (Amaranthus) in Ontario. I. Interspecific and intraspecific variation in seed germination among local collections of A. powellii and A. retroflexus. Canadian Journal of Botany, 53, 1276-1284.
12. Hendricks, S.B. and Taylorson, R.B. (1974). Promotion of seed germination by nitrate, nitrite, hydroxylamine and ammonium salts. Plant Physiology, 54, 304-309.
13. Hendricks, S.B. and Taylorson, R.B. (1975). Breaking of seed dormancy by catalase inhibition. Proceedings of the National Academy of Science, USA, 72, 306-309.
14. Hendricks, S.B. and Taylorson, R.B. (1976). Variation in germination and amino acid leakage of seeds with temperature related to membrane phase change. Plant Physiology, 58, 7-11.
15. Holm, R.E. and Miller, M.R. (1972). Weed seed germination responses to chemical and physical treatments. Weed Science, 20, 150-153.
16. Huang, H. (1981). [Effects of temperature on germination, growth and dry matter contents of two tropical vegetables with high nutritive value - edible amaranth and water convolvulus.] Memoirs of the College of Agriculture, National Taiwan University, 21, 88-105.
17. Kadman-Zahavi, A. (1955). The effect of light and temperature on the germination of Amaranthus blitoides seeds. Bulletin of the Research Council of Israel, 4, 370-374.
18. Kadman-Zahavi, A. (1960). Effect of short and continuous illumination on the germination of Amaranthus retroflexus seeds. Bulletin of the Research Council of Israel, Series D, 9, 1-20.
19. Kendrick, R.E. and Frankland, B. (1969). Photocontrol of germination in Amaranthus caudatus. Planta, 85, 326-339.
20. Kigel, J., Gibly, A. and Negbi, M. (1979). Seed germination in Amaranthus retroflexus L. as affected by the photoperiod and age during flower induction of the parent plants. Journal of Experimental Botany, 30, 997-1002.
21. Kigel, J., Ofir, M. and Koller, D. (1977). Control of the germination responses of Amaranthus retroflexus L. seeds by their parental photothermal environment. Journal of Experimental Botany, 28, 1125-1136.
22. Martin, J.N. (1943). Germination studies of the seeds of some common weeds. Proceedings of the Iowa Academy of Science, 50, 221-2 28.
23. Moursi, M.A., Rizk, T.Y. and El-Deepah, H.R. (1977). Weed seed germination responses to some chemical treatments. Egyptian Journal of Agronomy, 2, 197-209.
24. Popova, D. (1979). [Effect of light at constant and variable temperature conditions on the germination of green amaranth (Amaranthus retroflexus L.) and barnyard grass (Echinochloa crusgalli L.) seeds.] Plant Science, Sofia, 16, 39-48.
25. Roberts, E.H. (1964). The distribution of oxidation-reduction enzymes and the effects of respiratory inhibitors and oxidising agents on dormancy in rice seed. Physiologia Plantarum, 17, 14-29.
26. Santelmann, P.W. and Evetts, L. (1971). Germination and herbicide susceptibility of six pigweed species. Weed Science, 19, 51-54.
27. Sakanishi, Y. (1957). Studies on the germination behavior of some annual and biennial flower seeds. Bulletin of the University of Osaka Prefecture, Series B, 7, 23-28.
28. Schonbeck, M.W. and Egley, G.H. (1980). Redroot pigweed (Amaranthus retroflexus) seed germination responses to afterripening, temperature, ethylene, and some other environmental factors. Weed Science, 28, 543-548.
29. Schonbeck, M.W. and Egley, G.H. (1981). Phase-sequence of redroot pigweed seed germination responses to ethylene and other stimuli. Plant Physiology, 68, 175-179.
30. Schonbeck, M.W. and Egley, G.H. (1981). Changes in sensitivity of Amaranthus retroflexus L. seeds to ethylene during preincubation. I. Constant temperatures. Plant, Cell and Environment, 4, 229-235.
31. Schonbeck, M.W. and Egley, G.H. (1981). Changes in sensitivity of Amaranthus retroflexus L. seeds to ethylene during preincubation. II. Effects of alternating temperature and burial in soil. Plant, Cell and Environment, 4, 237-242.
32. Takabayashi, M. and Nakayama, K. (1981). [The seasonal change in seed dormancy of main upland weeds.] Weed Research, Japan, 26, 249-253.
33. Taylorson, R.B. (1970). Changes in dormancy and viability of weed seeds in soils. Weed Science, 18, 265-269.
34. Taylorson, R.B. (1979). Response of weed seeds to ethylene and related hydrocarbons. Weed Science, 27, 7-10.
35. Taylorson, R.B. and Hendricks, S.B. (1969). Action of phytochrome during pre-chilling of Amaranthus retroflexus L. seeds. Plant Physiology, 44, 821-825.
36. Taylorson, R.B. and Hendricks, S.B. (1971). Changes in phytochrome expressed by germination of Amaranthus retroflexus L. seeds. Plant Physiology, 47, 619-622.
CELOSIA
|
C. argentea L. |
|
|
C. cristata L. [C. argentea L. var
cristata (L.) Kuntze] |
cockscomb |
I. Evidence of dormancy
Seeds of Celosia spp. exhibit dormancy (2,3), even after 70 or 80 days' storage at 30°C (3).
II. Germination regimes for non-dormant seeds
C. argentea
TP: 20°/30°C (16h/8h); 20°C: 14d (ISTA)
TP: 20°/30°C (16h/8h): 28d (AOSA)
C. cristata
TP: 20°/30°C (16h/8h): 28d (AOSA)
III. Unsuccessful dormancy-breaking treatments
C. cristata
Constant temperatures: 15°C, 21°C, light, 12h/d, 80-100 W cm-2 (2); 20°C in light or dark (3)
Alternating temperatures: 41°/15°C (day/night) in light, 12h/d, 80-100 W cm-2 (2)
IV. Partly-successful dormancy-breaking treatments
C. argentea
Constant temperatures: 28°C in light, continuous, 1000 lux (4)
C. cristata
Constant temperatures: 30°C in light or dark (3); 31°C, 41°C, light, 12h/d, 80-100 W cm-2, 25d (2)
Alternating temperatures: 33°/21°C (day/night), light, 12,24h/d, 80-100 W cm-2, 30d (2); 31°/21°C, 41°/21°C, 41°/31°C (day/night) in light, 12h/d, 80-100 W cm-2, 25d (2) Light: (3)
V. Successful dormancy-breaking treatments
C. argentea
Pre-chill (ISTA)
Light (AOSA)
Alternating temperatures: 20°/30°C (16h/8h) in light, 10d (1)
C. cristata
Light (AOSA)
VI. Comment
High temperatures and light promote the germination of dormant seeds of Celosia spp. (2,3). An alternating temperature regime of 31°/21°C is better than 41°/21°C, 41°/31°C or 41°/15°C (day/night) (2), and better than constant temperatures between 15° and 41°C (2). If it is not possible to provide an alternating temperature regime then 30°C or 31°C is the most suitable constant temperature for germination tests within this range (2,3). At 31°/21°C some germination occurs after 15 days in test (2). Consequently it is suggested that AOSA rules, rather than ISTA rules, be followed since the former prescribe a longer test duration. In addition AOSA directions indicate that the seeds are sensitive to drying - presumably because secondary dormancy is induced - and so germination test substrata should be checked regularly and re-wetted if necessary.
VII. References
1. Atwater, B.R. (1980). Germination, dormancy and morphology of the seeds of herbaceous ornamental plants. Seed Science and Technology, 8, 523-573.
2. Okusanya, O.T. (1980). Germination and growth of Celosia cristata L., under various light and temperature regimes. American Journal of Botany, 67, 854-858.
3. Sakanishi, Y. (1957). Studies on the germination behavior of some annual and biennial flower seeds. Bulletin of the University of Osaka Prefecture, Series B, 7, 23-28.
4. Bansal, R.P. and Sen, D.N. (1981). Differential germination behavior in seeds of the Indian Arid Zone. Folia Geobotanika et Phytotaxonomica, 16, 317-330.
