The Malvaceae comprise more than 1000 species of herbaceous plants, shrubs and trees within about 50 genera which provide fibres (e.g. Gossypium hirsutum L., cotton) and edible fruits (e.g. Hibiscus esculentus L., okra). The fruits are usually dry single-seeded schizocarps or capsules, but are sometimes berry-like. The seeds exhibit orthodox storage characteristics.
SEED DORMANCY AND GERMINATION
The seeds may possess an endosperm, but the major food storage organ is the cotyledons. The seed coats are often hard and the embryo can be slow to develop during germination. B.R. Atwater classifies seed morphology as non-endospermic seeds with axile foliar embryos within hard seed coats (see Table 17.2, Chapter 17). Consequently treatments to seed coats which overcome hardseededness generally promote germination (see Chapter 7, Volume I).
In addition dormancy per se (that is innate seed dormancy, see Chapter 5, Volume I) can also prevent germination. Secondary dormancy may be induced when the seeds are tested for germination at low temperatures. Dormancy is minimised if the seeds are tested in alternating temperature regimes. The presence of both hardseededness and innate seed dormancy is sometimes described as double dormancy (see Chapter 5, Volume I).
Detailed information on seed dormancy and seed germination for the genera Gossypium, Hibiscus (including synonyms within Abelmoschus and Trionum), and Urena is provided in this chapter. Recommendations for germination test procedures and dormancy-breaking treatments for other species are summarised in Table 46.1. In addition the algorithm below may be helpful in developing suitable germination test procedures for some accessions.
RBG Kew Wakehurst Place algorithm
The first step in the algorithm is to test seeds at constant temperatures of 11°C, 21°C and 31°C with light applied for 12h/d.
If the above regimes do not promote full germination then the second step in the algorithm is to chip a fresh sample of seeds and then test at the constant temperature regime which gave the greatest germination in step one: test at 21°C if no significant differences in germination were observed in step one. Imbibition injury (see Chapter 4, Volume I) may occur in malvaceous species, particularly where the seed coats have been chipped. Consequently it may advantageous to humidify (condition) the seeds after chipping the seed coats and before imbibition. Chapter 7, Volume I, provides details of a suitable humidification treatment.
If the second step of the algorithm does not result in full germination then the third step of the algorithm is to experiment with the above conditions and test fresh samples of seeds in darkness and/or in alternating temperature regimes. The alternating temperature regimes 20°/30°C (16h/8h) and 15°/35°C (16h/8h) are suggested. If a comparison of the results of steps one and two shows chipping to be beneficial, then chip (and possibly humidify) the seeds before testing in darkness and/or alternating temperatures.
If full germination has not been promoted, the fourth 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 Gossypium, Hibiscus and Urena and from Table 46.1.
TABLE 46.1 Summary of germination test recommendations for species within the Malvaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Abutilon x hybridum Hort. |
TP; BP |
20°/30°C; 20°C |
21d |
|
ISTA |
|
Abutilon theophrasti Medic.
|
TP; S |
3°/35°C |
7d |
pre-soak, 100°C, 0.5-1 min, or pre-chill, 2°-5°C, 2d |
Everson |
|
|
|
|
pre-soak, 70°C, 30s, or pre-dry, 95°C, 6 min |
Atwater |
|
|
Alcea rosea L. |
TP; BP |
20°/30°C; 20°C |
21d |
pierce, chip or file cotyledon end of testa |
ISTA |
|
BP |
20°C |
18d |
continue test for a further 5d if (reversible) hard |
AOSA |
|
|
|
|
|
seeds have begun to imbibe |
|
|
|
|
20°C |
21d |
remove calyx, clip hard seeds |
Atwater |
|
|
Althaea x hybrida Hort. |
TP; BP |
20°/30°C; 20°C |
21d |
pierce, chip or file cotyledon end of testa |
ISTA |
|
Althaea officinalis L. |
TP; BP |
20°/30°C; 20°C |
21d |
pierce, chip or file cotyledon end of testa |
ISTA |
|
Lavatera trimestris L.
|
TP; BP |
20°/30°C; 20°C |
21d |
pre-chill |
ISTA |
|
BP |
20°C |
21d |
continue test for a further 5d if (reversible) hard |
AOSA |
|
|
|
|
|
seeds have begun to imbibe |
AOSA |
|
|
Malope trifida Cav. |
TP; BP |
20°/30°C; 20°C |
14d |
pre-chill |
ISTA |
GOSSYPIUM
|
G. anomalum Wawra & Peyr. |
wild cotton |
|
G. arboreum L. [G. obtusifolium Roxb.; G.
Nanking Meyen; G. indicum Lam.] |
Ceylon cotton, Chinese cotton, tree cotton |
|
G. armourianum Kearney |
wild cotton |
|
G. barbadense L. [G. peruvianum Cav.; G.
vitifolium Lam.] |
sea-island cotton |
|
G. barbadense L. var darwinii Hutch. |
wild cotton |
|
G. herbaceum L. |
Levant cotton, asiatic cotton |
|
G. hirsutum L. [G. mexicanum Tod.] |
upland cotton |
|
G. hirsutum L. var marie-galante (Watt)
Hutch. |
tree cotton |
|
G. hirsutum L. x G. barbadense L. |
American-Egyptian cotton |
|
G. klotzschianum Anders. var davidsonii
Hutch. |
wild cotton |
|
G. raimondii Ulb. |
wild cotton |
|
G. thurberi Tod. |
wild cotton |
I. Evidence of dormancy
Standard germination tests on seeds of Gossypium spp. are often plagued by low, delayed and/or erratic germination with additional problems from fungi (1,8,9,12,16). Freshly harvested seeds and those dried below 10% moisture content are generally the more difficult to germinate since they are extremely sensitive to the conditions of the germination test (16). These germination test difficulties result from both dormancy and hardseededness.
At harvest seeds of the cultivated Gossypium spp. can show considerable dormancy, viz. G. barbadense (17), G. herbaceum (9), G. hirsutum (3-6,10-12,14,16,17) and G. hirsutum x G. barbadense (5). Dormancy is reported to be lost after 1 (6,11), 1-5 (5), 2-3 (10) or 24 months (15) after-ripening. In addition secondary dormancy may be induced at low germination test temperatures (7,15), under high salt concentrations (15), or if there is excess moisture during imbibition (16). In the latter case the reported secondary dormancy may be increased hardseededness in the population.
Hardseededness is induced in the majority of seeds of the cultivated Gossypium spp. when dried to 5 or 6% moisture content (16). In addition all wild forms of the cultivated spp. and most wild Gossypium spp. have impermeable seed coats at low moisture contents (3,14,17). In general the wild spp. have much thicker seed coats than the cultivated spp. (14) and consequently greater proportions of individual seeds of the former are hardseeded than the latter (17). Thus gene banks must assume that hardseededness is present in all cases and take steps to make the seed coats permeable, with more severe treatments being necessary for the wild spp. than for the cultivated spp.
II. Germination regimes for non-dormant seeds
Gossypium spp.
BP; S: 20°/30°C (16h/8h); 25°C: 12d (ISTA)
BP; S: 20°/30°C (16h/8h): 12d (AOSA)
BP; S: 30°C: 8d (AOSA)
III. Unsuccessful dormancy-breaking treatments
G. hirsutum
Constant temperatures: 13°C (15)
Light: white, continuous (13); red, 1,4,8 min, after 8,12,16h dark imbibition (13)
Sodium chloride: co-applied, 9000 ppm, plus calcium chloride, 9000 ppm, at 25°C (15)
Scarification: mechanical, after acid delint (12)
IV. Partly-successful dormancy-breaking treatments
G. barbadense
Pre-soak: shake, drain, blot (7); 1h, after acid delint, then calcium chloride, co-applied, 10-5 M, at 15°C (8)
G. herbaceum
Pre-chill: 5°C, 71d (9)
G. hirsutum
Constant temperatures: 20°C, dark (1)
Alternating temperatures: 20°/30°C (16h/8h) (1); 18°/32°C (16h/8h, 8h/16h) (16); 13°/15°-21°C (16h/8h), after acid delint (2)
Pre-soak: shake, drain, blot (7); 1h, after acid delint, then calcium chloride, co-applied, 10-5 M, at 15°C (8)
Pre-dry: (11)
Ultrasonics: 90 kc/s, 30 min, germinate at 20°/30°C (16h/8h) (1)
Light: dark (13); far red, 4,8, min, after 8,12,16h dark imbibition (13)
V. Successful dormancy-breaking treatments
G. anomalum
Removal of seed covering structures: chip (14)
Pre-soak: hot water (14)
G. arboreum
Constant temperatures: 25°-30°C, after acid delint (7)
G. armourianum
Removal of seed covering structures: chip (14)
Pre-soak: hot water (14)
G. barbadense
Constant temperatures: 25°-30°C, after acid delint (7)
Alternating temperatures: 16°/21°C, 16°/27°C, 16°/30°C, 19°/21°C, 19°/27°C, 19°/30°C, 13°/27°C, 13°/30°C (16h/8h), after acid delint (2)
Pre-soak: 85°C, 1 min (17); 80°-90°C, 0.5-2 min (17); 1h, after acid delint, then calcium chloride, co-applied, 10-5 M, at 25°C (8)
G. barbadense var darwinii
Pre-soak: hot water (14)
Removal of seed covering structures: chip (14)
G. hirsutum
Constant temperatures: 20°C, 25°C, (16); 25°-30°C, after acid delint (7)
Alternating temperatures: 20°/30°C (16-18h/8-6h) (16); 15°/35°C (18h/6h) (16); 16°/21°C, 16°/27°C, 16°/30°C, 19°/21°C, 19°/27°C, 19°/30°C, 13°/27°C, 13°/30°C (16h/8h), after acid delint (2)
Pre-soak: 85°C, 1 min (17); 80°-90°C, 0.5-2 min (17); shake, drain, blot, germinate at 20°/30°C (16h/8h) (16); 1h, after acid delint, then calcium chloride, co-applied, 10-5 M, at 25°C (8)
Scarification: concentrated sulphuric acid, 5-8 min (12); ethanol (3); ether (3)
Removal of seed covering structures: seed coat (12); prick (3)
G. hirsutum var marie-galante, G. klotzschianum var davidsonii, G. raimondii
Pre-soak: hot water (14)
Removal of seed covering structures: chip (14)
G. thurberi
Pre-soak: hot water (14); 85°C, 1 min (17); 80°-90°C, 0.5-2 min (17)
VI. Comment
The term acid delint is used by many authors to describe a procedure which dissolves the lint and fuzz fibres of the seed coat and also removes other external contamination: it is frequently recommended as a means of seedling disease control (12). A typical treatment is 5 to 8 minutes immersion in sulphuric acid. Such treatments dissolve the cotton fibres and their basal cells, and in addition the epidermal and outer pigment layers of the seed coat are broken and distorted. The subsequent rate of imbibition (and hence germination) is increased, mainly due to closer contact between seeds and the germination test substratum in the absence of the fuzz. However, some accessions are damaged by acid delint treatments (12).
As an alternative to the acid delint treatment AOSA, ISTA (1976 Rules) and others (16) have recommended saturating the lint with moisture (pre-wetting) - by soaking and/or shaking the seeds in water or by subjecting seeds to a moist atmosphere using mist propagation equipment, with excess moisture being removed by the use of blotting paper. Whilst this increases the rate of imbibition (at least if the seeds are not hard), the germination of seeds of Gossypium spp. is very sensitive to excess moisture (8,12,16). Moreover, neither acid delinting nor pre-wetting can totally avoid the problem of hardseededness which, in seeds at 5% moisture content, is likely to be pronounced.
Consequently the following sequence of pre-germination test treatments is recommended for use in gene banks where seeds have been dried to low moisture contents: first scarify the seeds by chipping or sanding away a piece of the seed coat, or by piercing the seed coat with a needle; then humidify the seeds at ambient temperature and 95-100% relative humidity. A 24-48 hour humidification treatment for scarified seeds is sufficient to raise seed moisture content from around 6 to 12% moisture content (4). Provided seed moisture content is at or above 12% moisture content there should be no problems in the subsequent germination test (16). Seeds destined for field or glasshouse sowings should also be pre-treated as described.
Provided low temperatures are avoided - at which secondary dormancy may be induced (7,15) - full germination occurs over a fairly wide range of alternating and constant temperatures, viz. 20°/30°C (16h/8h), 15°/35°C (18h/6h), 20°C, 25°C (16). The major effect of seed dormancy appears to be one of delay to germination under such regimes rather than a failure to germinate (12). Thus it is suggested that the pre-treated seeds be tested for germination at the alternating temperature regime prescribed by AOSA/ISTA - 20°/30°C (16h/8h) - for at least 14 days.
VII. References
1. Andersen, A.M., Hart, J.R. and French, R.C. (1964). Comparison of germination techniques and conductivity tests of cotton seeds. Proceedings of the International Seed Testing Association, 29, 81-96.
2. Anderson, W.K. (1971). Emergence and early growth response of cotton to controlled temperature regimes. Cotton Growing Review, 48, 104-115.
3. Christiansen, M.N. and Moore, R.P. (1959). Seed coat structural differences that influence water uptake and seed quality in hard seed cotton. Agronomy Journal, 51, 582-584.
4. Christiansen, M.N., Moore, R.P. and Rhyne, C.L. (1960). Cotton seed quality preservation by a hard seed coat characteristic which restricts internal water uptake. Agronomy Journal, 52, 81-84.
5. Christidis, B.G. (1955). Dormancy in cotton seed. Agronomy Journal, 47, 400-403.
6. Hsi, D.C.H. and Reeder, H.M. (1953). Dormancy of upland and American-Egyptian cottonseed. Agronomy Journal, 45, 454.
7. Ludwig, C.A. (1932). The germination of cotton seed at low temperatures. Journal of Agricultural Research, 44, 367-380.
8. Powell, R.D. and Morgan, P.W. (1973). A test system for the germination of cotton seed. Cotton Growing Review, 50, 268-273.
9. Prathapasenan, G., Kamalavalli, D. and Pathak, C.H. (1966). Retarded rate of germination in Digvijay cotton. Journal of Maharaja Sayajirao University, Baroda, 15, 1-3. [From Field Crop Abstracts, 1972, 25, 2423.]
10. Purseglove, J.W. (1968). Malvaceae, pp. 333-376. In Tropical Crops. Dicotyledons Longmans, London.
11. Simpson, D.M. (1935). Dormancy and maturity of cotton seed. Journal of Agricultural Research, 50, 429-434.
12. Simpson, D.M., Adams, C.L. and Stone, G.M. (1940). Anatomical structure of the cotton seed coat as related to problems of germination. U.S.D.A. Technical Bulletin 734, pp. 1-23.
13. Singh, G. and Garg, O.P. (1971). Effect of red, far-red radiations on germination of cotton seed. Plant and Cell Physiology, Japan, 12, 411-415.
14. Stephens, S.G. (1958). Salt water tolerance of seeds of Gossypium species as a possible factor in seed dispersal. American Naturalist, 92, 83-92.
15. Taylor, R.M. and Lankford, M.K. (1972). Secondary dormancy in cotton. Crop Science, 12, 195-196.
16. Toole, E.H. and Drummond, P.L. (1924). The germination of cotton seed. Journal of Agricultural Research, 28, 285-292.
17. Walhood, V.T. (1956). A method of reducing the hard seed problem in cotton. Agronomy Journal, 48, 141-142.
HIBISCUS
|
H. acetosella Welw. |
|
|
H. cannabinus L. |
kenaf, bimli, bimlipatum, jute, Deccan hemp |
|
H. coccineus Walt. |
|
|
H. esculentus L. [Abelmoschus esculentus (L.)
Moench] |
okra, lady's finger, gumbo, bhindi |
|
H. gossypinus Thunb. |
|
|
H. militaris Cav. |
|
|
H. moscheutos L. [H. oculiroseus
Britt.] |
|
|
H. mutabilis L. |
cotton rose, confederate rose |
|
H. pedunculatus L. |
|
|
H. sabdariffa L. |
roselle, Jamaican sorrel |
|
H. trionum L. [H. africanus Hort.; Trionum
trionum Woot. & Standl.] |
flower of an hour, shoo fly |
I. Evidence of dormancy
No reports of dormancy, hardseededness or other problems in germinating seeds of H. cannabinus and H. sabdariffa have been found in the literature. Apparently, most of the annual cultivated Hibiscus spp. produce few hard seeds (16), whereas hardseededness can be prevalent in seeds of the wild Hibiscus spp., viz. H. trionum (5,9,11,16), H. acetosella, H. gossypinus, H. militaris, H. pedunculatus, H. moscheutos, H. coccineus and H. mutabilis (16). Hardseededness can, however, be a problem for seeds of H. esculentus, causing slow and erratic germination (1,7,13): seeds of H. esculentus at 13% moisture content tend to show little or no hardseededness, but once the seeds have been dried to 4-6% moisture content hardseededness becomes prevalent (A). This suggests that hardseededness is a potential problem in seeds of all Hibiscus spp. dried to low moisture contents for long-term storage. In addition to hardseededness, seed dormancy is also a problem in germination tests of H. esculentus (A).
II. Germination regimes for non-dormant seeds
H. cannabinus
BP; S: 20°/30°C (16h/8h): 8d (ISTA)
BP: 20°/30°C (16h/8h): 8d (AOSA)
H. esculentus
BP; TP; S: 20°/30°C (16h/8h): 21d (ISTA)
BP: 20°/30°C (16h/8h): 14d (AOSA)
H. sabdariffa
Alternating temperatures: 25°/30°C, light, 24h/d, 16d (17)
H. trionum
TP; BP: 20°/30°C (16h/8h): 28d (ISTA)
Hibiscus spp.
BP: 20°/30°C (16h/8h): 21d (AOSA)
III. Unsuccessful dormancy-breaking treatments
H. esculentus
Warm stratification: 13°C, 10d, germinate at 15°/29°C (1)
Pre-soak: 12h (14); 24h, then 13°C, 10d, germinate at 15°/29°C (1); 38°-54°C, 3 min (4)
Scarification: concentrated sulphuric acid, 5-15 min (7); mechanical (4)
Acetone: pre-applied, 1h (14); pre-applied, 30 min, 95%, then 13°C, 10d, germinate at 15°/29°C (1); pre-applied, 20,40 min, 95% (2,4) Glycerine: pre-applied, 5-60 min, 5% (1)
H. pedunculatus
Scarification: concentrated sulphuric acid, 1-60 min (16)
H. trionum
Thiourea: co-applied, 0.25% (11)
IV. Partly-successful dormancy-breaking treatments
H. acetosella
Scarification: concentrated sulphuric acid, 1 min-8h (16)
H. coccineus
Scarification: concentrated sulphuric acid, 1-15 min, 2-8h (16)
H. esculentus
Pre-soak: 24h (10)
GA3: pre-applied, 12h, 100-400 ppm (12)
Indoleacetic acid: pre-applied, 12h, 10-40 ppm (12)
Napthaleneacetic acid: pre-applied, 12h, 5-30 ppm (12)
Sodium bicarbonate: pre-applied, 24h, 0.1 M (10)
Calcium phosphate: pre-applied, 24h, 0.1 M (10)
Scarification: concentrated sulphuric acid, 0.5-3h (3,4); concentrated sulphuric acid, 30,60 min (7); concentrated sulphuric acid, 60 min (14); sulphuric acid, 50%, 30 min (1,10,14); hydrochloric acid, 50%, 1h (14); concentrated nitric acid, 1h (14); nitric acid, 50%, 30 min (14); hydrochloric acid, 50%, 1h (14); buttermilk, 30,60 min (14); acetone, 95%, 20,40 min (3); acetone, 95%, 30 min (10); alcohol, 95%, 30 min (10); mechanical (13)
H. gossypinus, H. militaris, H. moscheutos, H. mutabilis
Scarification: concentrated sulphuric acid, 1 min-8h (16)
H. pedunculatus
Scarification: concentrated sulphuric acid, 2-8h (16)
H. trionum
Constant temperatures: 25°C, 30°C (9)
Removal of seed covering structures: seed coat (9)
V. Successful dormancy-breaking treatments
H. coccineus
Scarification: concentrated sulphuric acid, 30 min (16)
H. esculentus
Constant temperatures: 15°-35°C (6); 25°C, dark (8, 15)
Alternating temperatures: 15.5°/29°C, 15.5°/32°C (night/day) (1)
Pre-soak: 24h (1, 14)
Removal of seed covering structures: part of testa (7)
Scarification: concentrated sulphuric acid, 30 min (14); concentrated sulphuric acid, 3h (7); sulphuric acid, 50%, 1h (14); concentrated hydrochloric acid, 0.5, 1h (14); hydrochloric acid, 50%, 30 min (14); concentrated nitric acid, 30 min (14); nitric acid, 50%, 1h (14); acetone, 95%, 5 min (1); acetone, 30 min (14); alcohol, 95%, 5 min (1); alcohol, 0.5, 1h (14)
H. sabdariffa
Pre-soak: 24h (18)
H. trionum
Scarification: concentrated sulphuric acid, 20 min, germinate at 20°C/30°C (16h/8h) (5)
VI. Comment
Seed scarification is reported to be necessary to allow germination to occur in H. esculentus and the wild Hibiscus spp. (1-3,5,7,9,10, 13,14,16). The rules of the AOSA note that hard seeds may be present when seeds of the Hibiscus spp. cultivated as flowers are tested for germination and direct that germination tests be continued for an additional 5 days. Although hardseededness does not appear to be a major problem in H. cannabinus, it is possible that seeds dried to 5% moisture content for long-term storage may exhibit hardseededness. Acetone or sulphuric acid are commonly used in scarification treatments and are generally successful, but appropriate concentrations and treatment durations vary considerably between species and between accessions within a single genotype (3,4,16); with concentrated sulphuric acid 30 minute treatments are probably the most satisfactory (16), although 2 hour treatments are required for H. mutabilis and H. pedunculatus (16). In view of these differences and the difficulty in obtaining full germination with such treatments it is not suggested that gene banks acid scarify seeds of Hibiscus spp.
For H. esculentus 25°C is the most suitable constant temperature germination test regime (6,8,15), but - as with other species in which hardseededness is a problem - alternating temperature regimes are preferable to constant temperatures (1). It is suggested that the seeds be tested for germination under the ISTA/AOSA prescribed alternating temperature regime of 20°/30°C (16h/8h), and that these tests be inspected after 4 or 5 days and the non-imbibed seeds scarified by hand and then returned to the germination test. Where a high proportion of seeds with impermeable seed coats is expected, it is suggested that all seeds be scarified by hand and then humidified at 95 to 100% relative humidity for 24 hours prior to the germination test.
VII. References
1. Anderson, W.H., Carolus, R.L. and Watson, D.P. (1953). The germination of okra seed as influenced by treatment with acetone and alcohol. Proceedings of the American Society for Horticultural Science, 62, 427-432.
2. Edmond, J.B. and Drapala, W.J. (1958). The effect of temperature, sand and soil, and acetone on germination of okra seed. Proceedings of the American Society for Horticultural Science, 71, 428-434.
3. Edmond, J.B. and Drapala, W.J. (1959). The effect of temperature, immersion in acetone, and sulphuric acid on germination of five varieties of okra seed. Proceedings of the American Society for Horticultural Science, 74, 601-606.
4. Edmond, J.B. and Drapala, W.J. (1960). Studies of the germination of okra seed. Mississipi Agricultural Experiment Station Technical Bulletin, 47, 1-15.
5. 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.
6. Harrington, J.F. (1963). The effect of temperature on the germination of several kinds of vegetable seeds. Proceedings of the 16th International Horticultural Congress, 2, 435-441.
7. Johnston, A. (1949). The germination of malvaceous seeds. Tropical Agriculture, Trinidad, 26, 63.
8. Manohar, M.S. (1969). Pod development and germination of bhindi (Abelmoschus esculentus). Experimental Agriculture, 5, 249-255.
9. Martin, J.N. (1943). Germination studies of the seeds of some common weeds. Proceedings of the Iowa Academy of Science, 50, 221-22 8.
10. Medina, P.V.L., Medina, R.M.T. and Shimoya, C. (1972). [Okra seedcoat anatomy and the use of chemicals to hasten germination.] Revista Ceres, 19, 385-394. (From Horticultural Abstracts, 1974, 44, 475.)
11. 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.
12. Omran, A.F., El-Bakry, A.M. and Gawish, R.A. (1980). Effect of soaking seeds in some growth regulator solutions on the growth, chemical constituents and yield of okra. Seed Science and Technology, 8, 161-168.
13. Rose, D.H. (1915). A study of delayed germination in economic seeds. Botanical Gazette, 59, 425-444.
14. Singh, K. and Singh, A. (1969). Effect of various chemicals on the germination of some hard-coated vegetable seeds. Journal of Research, Ludhiana, 6, 801-807.
15. Solanki, S.S., Singh, R.D. and Yadav, J.P. (1980). Studies on the temperature and media relations and coefficient velocity of germination of vegetable seeds. II. Summer squash (Cucurbita pepo L.) and okra (Abelmoschus esculentus (L.) Moench.). Progressive Horticulture, 12, 59-65.
16. Tachibana, Y. (1961). [Studies in Hibiscus. IV. Further studies on the method of promoting seed germination.] Journal of the Japanese Society for Horticultural Science, 30, 183-188.
17. Chin, H.F., Hor, Y.L. and Mohd Lassim, M.B. (1984). Identification of recalcitrant seeds. Seed Science and Technology, 12, 429-436.
18. Riley, J.M. (1981). Growing rare fruit from seed. California Rare Fruit Growers Yearbook, 13, 1-47.
URENA
U. lobata L. aramina fibre, Congo jute
I. Evidence of dormancy
Germination of seeds of U. lobata is slow, erratic and low (1,4-8). Field sowings take 2-3 months to germinate (1). Hardseededness is reported to be the cause of these problems (4-8).
II. Germination regimes for non-dormant seeds
Constant temperatures: 30°C in light (2,3,9,10)
Alternating temperatures: 20°/30°C (night/day) (7)
III. Unsuccessful dormancy-breaking treatments
Pre-chill: 5°-10°C, 3d (4)
Pre-soak: 12h (4); 12-48h, then pre-chill, -10°C, 6h (7); 36,48h, then pre-chill, -10°C, 2h (7)
Ethanol: pre-applied, 2,3h, 95% (7); pre-applied, 5 min-3h, 95%, to dehulled seeds (7)
Ethyl ether: pre-applied, 5 min-3h, 1.5% (7); pre-applied, 5 min-3h, 1.5%, to dehulled seeds (7)
Scarification: concentrated sulphuric acid, 5-15 min, 12,24h (7)
Removal of seed covering structures: dehull, then concentrated sulphuric acid scarification, 2 min (7); dehull, then concentrated sulphuric acid scarification, 5,6h, then pre-soak, 48h (6)
IV. Partly-successful dormancy-breaking treatments
Removal of seed covering structures: carpel (7); carpel, then pre-soak, 1,2d (6,8)
Pre-soak: 12,24h, then pre-chill, -10°C, 2h (7)
Ethanol: pre-applied, 4h, 95% (4); pre-applied, 5 min-1h, 95% (7)
Formol: pre-applied, 2h, 40% (4)
Acetone: pre-applied, 4h, 95% (4)
Sodium hypochlorite: pre-applied, 24h, 1% (4)
Potassium nitrate: pre-applied, 12h, 0.2% (4); co-applied, 0.3% (4)
Scarification: nitric acid, 10-2 N, 10 min (4); concentrated hydrochloric acid, 15 min (4); concentrated sulphuric acid, 0.5-2h (7); concentrated sulphuric acid, 5 min-1.5h, 4-6h, then pre-soak, 48h (6); sulphuric acid, 0.1%, 12h (4); mechanical, 1425-1725 rpm, 10s (4); concentrated sulphuric acid, 30 min, germinate at 20°C, 25°C, 35°C, 20°/30°C, 20°/35°C (16h/8h), dark or light, 8h/d, 4d (2)
Removal of seed covering structures: small part of testa, germinate at 21°/31°C (night/day) (5); dehull, then concentrated sulphuric acid scarification, 0.5-2h (7); dehull, then concentrated sulphuric acid scarification, 5-30 min, 1.5-4h, then pre-soak, 48h (6)
Light: 5 min (4)
Pre-dry: 90°C, 2h (4); 90°/2°C (2h/2h) (4)
V. Successful dormancy-breaking treatments
Pre-soak: 100°C, then 30°C, 40 min (4)
Scarification: concentrated sulphuric acid, 30 min, then pre-wash, 10 min, germinate at 30°C, light, 8h/d (2,3,4,9,10); concentrated sulphuric acid, 3,4h (7); concentrated sulphuric acid, 2,3h, then pre-soak, 48h (6)
Removal of seed covering structures: dehull, then concentrated sulphuric acid scarification, 1h, then pre-soak, 48h (6)
VI. Comment
It is suggested that the carpel (hull) be removed from seeds, a small portion of the testa be removed or scarified by hand, and the seeds then tested for germination in an alternating temperature regime of 20°/30°C (16h/8h) in light.
VII. References
1. Crane, J.C. and Acuna, J.B. (1945). Effect of planting rate on fiber yield of Urena lobata L. as compared with kenaf, Hibiscus cannabinus L. Journal of the American Society of Agronomy, 37, 245-250.
2. Figueiredo, F.J.C. and Popinigis, F. (1978). Temperature de germinaçáo para sementes de malva (Urena lobata L.). EMBRAPA/ CPATU, Comunicado Tecnico No. 14, 20 pp.
3. Figueiredo, F.J.C. and Popinigis, F. (1978). Substrato de germinaçáo para sementes de malva (Urena lobata L.). EMBRAPA/CPATU, Comunicado Tecnico No. 18, 10 pp.
4. Figueiredo, F.J.C. and Popinigis, F. (1979). Superaçáo da dormencia de sementes de malva. Revista Brasileira de Sementes, 1, 1-13.
5. Harris, P.J.C. (1981). Seed viability, dormancy, and field emergence of Urena lobata L. in Sierra Leone. Tropical Agriculture, 58, 205-213.
6. Horn, C.L. and Colon, J.E.N. (1942). Acid scarification of the seed of two cuban fiber plants. Journal of the American Society of Agronomy, 34, 1137-1138.
7. Juillet, A. (1952). Etude de la germination d'Urena lobata. Agronomie Tropicale, 7, 487-507.
8. Kirby, R.H. (1963). Vegetable fibres: Botany, cultivation and utilization, Leonard Hill, London.
9. Figueiredo, F.J.C. and Popinigis, F. (1980). Substrato de germinaçáo para sementes de malva. Revista Brasileira de Sementes, 2, 11-17.
10. Figueiredo, F.J.C. and Popinigis, F. (1980). Duraçáo de teste de germinaçáo do sementes de malva. Revista Brasileira de Sementes, 2, 53-57.
