The Tiliaceae comprise about 400 species of trees, shrubs and, rarely, herbaceous plants within more than 35 genera, some of which provide fibres (e.g. Cephalonema polyandrum K. Schum.). The fruits are capsules, berries or drupes and the seeds show orthodox storage behaviour. For example, Corchorus fructicosus is maintained in the long-term seed store at the Wakehurst Place Gene Bank. Incidentally, comments that seeds of certain Corchorus spp. should not be stored at moisture contents below 10% are erroneous and result from researchers confounding hardseededness (see below) with loss in viability.
SEED DORMANCY AND GERMINATION
Hardseededness is likely to be the most prevalent problem in germination tests, but can be avoided by suitable treatments to the seed covering structures (e.g. chipping off a part of the seed coat). Comparatively high temperatures are required for germination tests. Detailed information on seed dormancy and germination is provided in this chapter for the genus Corchorus. A summary of recommended germination test procedures and dormancy-breaking treatments for other species is provided in Table 70.1. In addition the algorithm below may be helpful in developing suitable germination test procedures.
RBG Kew Wakehurst Place algorithm
The first step in the algorithm is to test seeds at constant temperatures of 31°C and 36°C with light applied for 12h/d.
If the first step of the algorithm does not result in full germination then the second step is to chip the seed coats of a further sample of seeds and then test for germination at the constant temperature regime which resulted in the greater proportion of seeds germinating in step one. If there was no significant difference between the results at the two temperatures then test the chipped seeds at 31°C.
If the second step of the algorithm does not result in full germination then the third step is to co-apply 7 x 10-4 M GA3 to the germination test substrate and test a further sample of seeds at the most appropriate regime determined from a comparison of the results of steps one and two. This will include a requirement to chip the seeds if hard seeds are present in the accession.
TABLE 70.1 Summary of germination test recommendations for species within the Tiliaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Muntingia calabura L. |
|
|
21d |
pre-soak, 24h, then warm stratification |
Riley |
|
Tilia cordata Mill. |
S |
20°/30°C |
28d |
pre-chill, 3°-5°C, 6-9m |
ISTA |
|
Tilia platyphyllos Scop. |
S |
20°/30°C |
28d |
pre-chill, 3°-5°C, 6-9m |
ISTA |
|
Tilia spp. |
|
|
|
scarify, concentrated sulphuric acid, or soak in hot water,
70°C, 5 times G&R |
|
CORCHORUS
|
C. aestuans L. [C. acutangulus Lam.] |
|
|
C. capsularis L. |
white jute, jute |
|
C. depressus C. Chr. [C. antichorus
Raeusch.] |
|
|
C. mello |
|
|
C. olitorius L. |
tossa jute, nalta jute, jews-mallow |
|
C. trilocularis L. |
|
I. Evidence of dormancy
With the exception of a requirement for light (see Comment) there is no direct evidence of dormancy being a problem when germinating seeds of Corchorus spp., but seeds of the wild Corchorus spp. C. aestuans, C. depressus, and C. trilocularis can be hardseeded (4,10).
II. Germination regimes for non-dormant seeds
C. capsularis, C. olitorius
TP; S: 30°C: 5d (ISTA)
Constant temperatures: 30°C, light (3,8,9)
III. Unsuccessful dormancy-breaking treatments
C. aestuans
Constant temperatures: 30°C, light, continuous, 1000 lux (10)
Scarification: sulphuric acid (4); alcohol (4)
Pre-soak: 24h (4)
C. capsularis
GA3: pre-applied, 0.01, 0.1% (1)
Indoleacetic acid: pre-applied, 0.01, 0.1% (1)
C. depressus
Scarification: sulphuric acid (4); alcohol (4)
Pre-soak: 24h (4)
C. mello
2,4-Dichlorophenoxyacetic acid: pre-applied, 3,6h, 10, 20, 40 ppm (2)
C. olitorius
GA3: pre-applied, 0.01, 0.1% (1); co-applied, 50, 100 ppm (7)
Indoleacetic acid: pre-applied, 0.01, 0.1% (1)
C. trilocularis
Scarification: sulphuric acid (4); alcohol (4)
Pre-soak: 24h (4)
IV. Partly-successful dormancy-breaking treatments
C. aestuans
Scarification: sand paper, germinate in direct sunlight or shade (4)
Pre-dry: 70°C, 3-5d (10); 80°C, 2-5d (10); 90°C, 1-5d (10); 100°C, 2-4d (10); 110°C, 1-3d (10)
C. capsularis
Constant temperatures: 25°C, light (8); 25°C (9); 20°C, 25°C, light or dark (3)
Alternating temperatures: 20°/30°C (16h/8h) (9); 20°/30°C, 20°/35°C (16h/8h), light or dark (3)
GA3: co-applied, 200 ppm (6)
Potassium nitrate: pre-applied, 0.01, 0.1% (1)
Thiourea: pre-applied, 0.01, 0.1% (1)
C. depressus
Scarification: sandpaper, germinate in direct sunlight or shade (4)
C. mello
Colchicine: pre-applied, 3,6h, 20 ppm (2)
C. olitorius
Constant temperatures: 15°-41°C, light, 12h/d (5); 25°C in light, 8h/d (8); 25°C (9)
Alternating temperatures: 21°/31°C, 21°/41°C, 15°/41°C, 31°/41°C (12h/12h), light, 12h/d (5); 20°/30°C (16h/8h) (9)
GA3: co-applied, 200 ppm (6)
Indoleacetic acid: co-applied, 50, 100 ppm (7)
Kinetin: co-applied, 50 ppm (7)
Potassium nitrate: pre-applied, 0.01, 0.1% (1)
Thiourea: pre-applied, 0.01, 0.1% (1)
C. trilocularis
Scarification: sand paper, germinate in direct sunlight or shade (4)
V. Successful dormancy-breaking treatments
C. capsularis
Constant temperatures: 30°C, light (3,8,9); 35°C (9)
Alternating temperatures: 25°
C. mello
GA3: pre-applied, 3,6h, 50-200 ppm, at 30°C (2)
Colchicine: pre-applied, 3,6h, 5-10 ppm, at 30°C (2)
C. olitorius
Constant temperatures: 30°C, light (3,8,9); 35°C (9)
Alternating temperatures: 25°/35°C (16h/8h) (9)
VI. Comment
The most suitable seed germination test regime for Corchorus spp. appears to be a constant temperature of 30°C (2,3,5,8,9), as prescribed by ISTA. Alternating temperature regimes are, apparently, not superior to constant temperature germination test regimes (3,9), and may indeed be inferior in 40 day tests (5). Light is required for germination (3-5), although the effect may be only marginal. Consequently it is suggested that gene banks test seeds of Corchorus spp. for germination at 30°C with light applied for 8 hours per day. Hardseededness is likely to be a problem for some accessions, particularly those of the wild Corchorus spp. (4,10). It is suggested that the seed coats of non-imbibed seeds be scarified or pricked with a needle after 4 or 5 days in test, and the test continued for at least a further 5 days.
VII. References
1. Chakraverty, R.K. (1975). Germination, viability and seedling growth in two species of Corchorus. Science and Culture, 41, 393-395.
2. Fahmy, R. (1974). Soaking jute seeds in different concentrations of gibberellic acid, 2,4-D and colchicine and its effect on germination and organic compounds formed in the seedlings. Biochemie and Physiologie der Pflanzen, 165, 141-148.
3. Figueirêdo, F.J.C., Carvalho, J.E.U. De., Oliveira, R.P. De. and Frazâo, D.A.C. (1980). [Temperature and light in the germination of jute seeds.] Boletim de Pesquisa, Centro de Pesquisa Agropecuaria do Trópico Umido, 4, 1-16.
4. Islam, A.S. and Khan, M.I. (1957). Studies on the seed germination of Corchorus spp. Biologia, 3, 165-167.
5. Okusanya, O.T. (1979). Quantitative analysis of the effects of photoperiod, temperature, salinity and soil types on the germination and growth of Corchorus olitorius. Oikos, 33, 444-450.
6. Rahman, A. (1978). Effects of gibberellic acid on the germination of Corchorus capsularis and Corchorus olitorius. Bangladesh Journal of Scientific and Industrial Research, 13, 243-246.
7. Rizk, T.K., Fayed, M.T. and El-Deepah, H.R. (1978). Effect of some promoters on weed seed germination. Research Bulletin of the Faculty of Agriculture, Ain Shams University, 818, 1-30.
8. Singh, A., Karna, I. and Verma, K. (1972). Germination methods for jute seed. Proceedings of the International Seed Testing Association, 37, 793-796.
9. Verma, M.M. and Arora, N. (1978). Further studies on seed testing procedures for jute (Corchorus capsularis and C. olitorius seeds. Seed Research, 6, 151-157.
10. Chawan, D.D. and Sen, D.N. (1973). Diversity in germination behaviour and high temperature tolerance in the seeds of Corchorus aestuans Linn. Annals of Arid Zone, 12, 23-32.
