The Anacardiaceae comprise some 400 species of trees and shrubs in 60 genera which provide edible fruits (e.g. Mangifera indica L., mango) and nuts (e.g. Anacardium occidentale L., cashew), tannin (e.g. Schinopsis lorentzii (Griseb.) Engl., quebracho), lacquers (e.g. Rhus verniciflua Stokes) and mastics (e.g. Pistacia lentiscus L.). The fruits are usually indehiscent drupes - but with important exceptions, e.g. cashew. The seeds have fleshy cotyledons and little or no endosperm and the seed covering structures are usually hard. For example, mango seeds are surrounded by a stony endocarp.
Seed storage characteristics appear to differ within the Anacardiaceae. Some species show orthodox seed storage behaviour: for example cashew; and seeds of Schinus spp. are maintained in the long-term seed store of the Wakehurst Place Gene Bank. But other species, of which the best known example is the mango, are reported to exhibit recalcitrant seed storage characteristics.
SEED DORMANCY AND GERMINATION
B.R. Atwater classifies seed morphology as non-endospermic seeds with axile foliar embryos contained within hard seed coats (see Table 17.2, Chapter 17). Consequently a major improvement to the proportion of seeds germinating can generally be achieved by scarification or removal of the seed covering structures. Detailed information on seed germination is provided for the genera Anacardium and Pistacia in this chapter. A limited number of other recommended germination test procedures is provided in Table 21.1 and the algorithm below may be helpful in developing suitable germination test procedures.
RBG Kew Wakehurst Place algorithm
In this algorithm the seed covering structures are chipped before any germination test is begun. The first step of the algorithm is to test one sample of the chipped seeds at a constant temperature of 21°C with light applied for 12h/d and a second sample in an alternating temperature regime of 23°/9°C (12h/12h) with light applied for 12h/d during the period spent at the upper temperature.
If neither regime promotes full germination then the second step of the algorithm is to test a further sample of chipped seeds in the more successful of the two regimes applied in the first step, but with 7 x 10-4 M GA3 co-applied to the germination test substrate.
TABLE 21.1 Summary of germination test recommendations for species within the Anacardiaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Harpephyllum caffrum Bernh. |
|
|
21d |
complete removal of seed covering structures |
Riley |
|
Mangifera indica L.
|
S |
25°-30°C |
28d |
light, continuous |
CHML |
|
|
|
21d |
complete removal of seed covering structures, then pre-soak, 24h |
Riley |
|
|
Rhus integrifolia Benth. & Hook. |
soil |
|
11d |
scarify, concentrated sulphuric acid, 4h |
Atwater |
|
Rhus ovata Wats. |
|
|
|
scarify, concentrated sulphuric acid, 3h, or drill a hole |
Atwater |
ANACARDIUM
|
A. occidentale L. |
cashew |
I. Evidence of dormancy
Seed dormancy per se in A. occidentale - an orthodox species (5,7) - has not been reported, but germination is often low and delayed (2,10).
II. Germination regimes for non-dormant seeds
-
III. Unsuccessful dormancy-breaking treatments
Constant temperatures: 10°C, 15°C (6)
Pre-soak: 2h (9); 6h (3)
Sodium bicarbonate: pre-applied, 2h, 5% (7)
Chloroform: pre-applied, 10+h (9)
Acetone: pre-applied, 10+h (9)
IV. Partly-successful dormancy-breaking treatments
Constant temperatures: 20°-40°C (6)
Pre-soak: 12-24h (3); 24,48h (5)
Sodium hydroxide: pre-applied, 2h, 1.6% (7)
Light: 12h/d, at 35°C (7)
V. Successful dormancy-breaking treatments
GA3: pre-applied, 48h, 100-500 ppm (8)
Chloroform: pre-applied, 2h (9)
Acetone: pre-applied, 2h (9)
Pre-soak: 24h (11)
VI. Comment
Slow imbibition of dry intact seeds is the main cause of delayed germination in cashew (9). The problem is greatest in the larger seeds (2,3,10). Pre-soaking for 1 or 2 days (3,5) or the removal of the waxy layer of the pericarp by treatment with chloroform or acetone (9) promote imbibition and thus reduce the time taken to germinate and increase the proportions of seeds germinating. Light (7) and gibberellins (8) are also reported to promote germination. If sand is used as the germination test medium it should be kept moist and well aerated (6); the seeds should be sown shallow with the concave side up or on one side, but not with the convex side up (1,3,4). The optimum constant temperature for germination is 35°C (6,7); germination at 30°C is similar to that at 35°C, but is substantially reduced at 40°C (6). It is suggested that the seeds be tested for germination in moist sand or between paper towels at about 32°C, that is between 30°-35°C, for at least 42 days, after pre-soaking for 24 hours.
VII. References
1. Adams, B.R. (1975). Container production of cashew seedling rootstocks. Seed germination in beds as an alternative to direct sowing. Acta Horticulturae, 49, 99-108.
2. Auckland, A.K. (1961). The influence of seed quality on the early growth of cashew. Tropical Agriculture, Trinidad, 38, 57-67.
3. Ibikunle, B.O. and Komolafe, D.A. (1973). Some experiments on the germination of cashew nuts (Anacardium occidentale Linn.). Nigerian Journal of Science, 7, 19-29.
4. Rao, V.N.M., Rao, I.K.S. and Hassan, M.V. (1957). Studies on certain aspects of germination of seeds in cashew (Anacardium occidentale Linn.). Indian Journal of Agricultural Science, 27, 25-34.
5. Rao, V.N.M., Rao, I.K.S. and Hassan, M.V. (1957). Studies on seed viability in cashew. Indian Journal of Agricultural Science, 27, 289-294.
6. Rocchetti, G. and Panerai, L. (1968). [The effect of temperature on the germination of cashew nuts.] Rivista di Agricoltura Subtropicale e Tropicale, 62, 228-235.
7. Rocchetti, G. and Panerai, L. (1970). [Further studies on the germination of the cashew nut.] Rivista di Agricoltura Subtropicale e Tropicale, 64, 151-160.
8. Shanmugavelu, K.G. (1970). Effect of gibberellic acid on seed germination and development of seedlings of some tree plant species. Madras Agricultural Journal, 57, 311-314.
9. Subbaiah, C.C. (1982/1983). Effect of presoaking in organic solvents on seed germination and seedling growth of cashew. Scientia Horticulturae, 18, 137-142.
10. Turner, D.J. (1956). Some observations on the germination and grading of cashew nut. East African Agricultural Journal, 22, 35-39
11. Riley, J.M. (1981). Growing rare fruit from seed. California Rare Fruit Growers Yearbook, 13, 1-47.
PISTACIA
|
P. atlantica Desf. |
|
|
P. chinensis Bunge |
|
|
P. integerrima Ste. [P. khinjuk Stock] |
|
|
P. lentiscus L. |
|
|
P. terebinthus L. |
|
|
P. vera L. [P. trifolia L.; P.
narbonnencis L.] |
pistachio |
I. Evidence of dormancy
Seeds of Pistacia spp. can show considerable dormancy (1,2,3,4,6,12,13). After-ripening for 1.5 years is required to remove dormancy (8).
II. Germination regimes for non-dormant seeds
-
III. Unsuccessful dormancy-breaking treatments
P. atlantica
Pre-soak: 10°-13°C, 1-21d (1)
Scarification: sand paper (3)
P. chinensis
Pre-chill: 3°C, 10°C, 90d (5)
P. integerrima
Scarification: concentrated sulphuric acid, 30 min (13); sulphuric acid, 10%, 12,24h (12)
P. terebinthus
Pre-soak: 7d (2); 3°-6°C, 7d, with or without epicarp (2) GA3: pre-applied, 7d, 50, 500 ppm (2)
Scarification: sand paper (3); concentrated sulphuric acid, 30 min, with or without epicarp, then pre-soak, 24h (2); concentrated sulphuric acid, 2h, then pre-soak, 24h (3)
P. vera
Removal of seed covering structures: epicarp, then GA3, pre-applied, 1d, 10°-13°C, 10 ppm (1); endocarp (2); endocarp, then GA3, pre-applied, 7,15d, 50, 500 ppm (2); endocarp, then pre-soak, 3°-6°C, 7, 15d (2)
IV. Partly-successful dormancy-breaking treatments
P. atlantica
Pre-soak: 2-3h, then remove epicarp and endocarp (10)
GA3: pre-applied, 7-21d, 100 ppm, 10°-13°C (1)
Removal of seed covering structures: epicarp, then pre-soak, 10°-13°C, 3-21d (1); epicarp, then pre-chill, 10°-13°C, 3-21d (1); epicarp, then GA3, pre-applied, 3-21d, 10-1000 ppm, 10°-13°C (1)
Scarification: concentrated sulphuric acid, 1.5h, then pre-soak, 24h (3)
P. chinensis
Pre-chill: 0°C, 30-90d (5); 3°C, 30d (5); 5°C, 30,90d (5)
Pre-soak: 1-2h (7)
Removal of seed covering structures: epicarp, then pre-soak, 10°-13°C, 1-21d (1); epicarp, then GA3, pre-applied, 1-21d, 500 ppm, 10°-13°C (1)
P. integerrima
Pre-chill: 3°-5°C, 15,30,45d (12)
Pre-soak: 100°C, then cool (13)
GA3: pre-applied, 24h, 50, 100 ppm (4)
Vitamin B9: pre-applied, 24h, 50 ppm (4)
Scarification: sand paper (4); sulphuric acid, 10%, 6h (12); sulphuric acid, 10%, 6,12,24h, then pre-chill, 3°-5°C, 15,30,45d (12); concentrated sulphuric acid, 15 min (13); concentrated sulphuric acid, 5,10,20 min, then pre-chill, 3°-5°C, 15d (12); concentrated sulphuric acid, 5,10 min, then pre-chill, 3°-5°C, 45d (12); concentrated sulphuric acid, 10 min, then pre-chill, 3°-5°C, 30d (12)
P. terebinthus
Pre-soak: 3°-6°C, 15d, with or without epicarp (2)
GA3: pre-applied, 7,15d, 50, 500 ppm (2)
Removal of seed covering structures: epicarp, then pre-soak, 10°-13°C, 1-21d (1); epicarp, then GA3, pre-applied, 1-21d, 500 ppm, 10°-13°C (1)
Scarification: concentrated sulphuric acid, 1.5h, then pre-soak, 24h (3)
P. vera
Pre-soak: 3°-6°C, 7,15d (2)
GA3: pre-applied, 3,7,14,21d, 100 ppm, 10°-13°C (1); pre-applied, 7,15d, 50, 500 ppm (2)
Removal of seed covering structures: epicarp, then pre-soak, 10°-13°C, 3-21d (1); epicarp, then GA3, pre-applied, 1-21d, 100, 1000 ppm, 10°-13°C (1); epicarp, then GA3, pre-applied, 7-21d, 10 ppm, 10°-13°C (1); epicarp, split endocarp, then pre-soak, 10°-13°C, 1,3,7,21d (1); epicarp, split endocarp, then GA3, pre-applied, 1,3,7,21d, 10-1000 ppm, 10°-13°C (1); epicarp, split endocarp, then pre-chill, 10°-13°C, 3-21d (1)
V. Successful dormancy-breaking treatments
P. atlantica
Pre-soak: (14); 1-2h (7); 2-3h (6); 2-3h, then remove epicarp and endocarp, then pre-chill, 2°-3°C, 4w, germinate at 20°C (10) Removal of seed covering structures: epicarp, then pre-soak, 10°-13°C, 1d (1); epicarp, then GA3, pre-applied, 1d, 10-1000 ppm, 10°-13°C, germinate at 21°/32°C (night/day) (1)
P. chinensis
Pre-chill: 3°C, 5°C, 60d (5); 10°C, 30d (5)
Pre-soak: 2-3h (6)
Removal of seed covering structures: epicarp, then pre-soak (14)
P. Integerrima
Pre-soak: 2-3h (6)
Vitamin B9: pre-applied, 24h, 100, 150 ppm (4)
GA3: pre-applied, 24h, 150 ppm (4)
Scarification: sand paper, then vitamin B9, pre-applied, 24h, 50-150 ppm (4); concentrated sulphuric acid, 5,20 min, then pre-chill, 3°-5°C, 30d (12); concentrated sulphuric acid, 20 min, then pre-chill, 3°-5°C, 45d (12)
P. lentiscus
Pre-soak: 2-3h (6)
P. terebinthus
Pre-chill: 5°C, 6w, germinate at 21°C (7)
Pre-soak: 2-3h, then warm stratification, 22°C, 2w (6, 14); 2-3h, then remove epicarp and endocarp, then pre-chill, 2°-3°C, 4w, germinate at 20°C (10)
P. vera
Pre-soak: 5°C, 2w (6,7,14); 2d, then remove epicarp and endocarp (11); 2-3h, remove epicarp and endocarp, then pre-chill, 2°-3°C, 4w, germinate at 20°C (10)
Pre-wash: 1-2d, then warm stratification, 22°C, 2w (6)
Removal of seed covering structures: epicarp, split endocarp, then pre-soak, 10°-13°C, 14d (1); epicarp, split endocarp, then GA3, pre-applied, 14d, 10-1000 ppm, 10°-13°C (1)
Pistacia spp.
Pre-soak: 15°-17°C, 24h (8); warm, 24h, then warm stratification, 1-2w (9)
VI. Comment
Pistacia spp. show orthodox seed storage characteristics (1,6,7,14). The seeds can be tested for germination on top of paper, between paper or in sand (4, 12). Non-dormant seeds germinate well at 21°C or below, poorly at 27°C, whilst no seeds germinate at 33°C (7) - with the exception of seeds of P. terebinthus which germinate well at 27°C (7). Consequently it has been suggested that non-dormant seeds of Pistacia spp. be tested for germination at a constant temperature of 20°C, between moist paper towels (7,10).
The seed covering structures can, however, represent a formidable barrier to embryo growth: the epicarp (the soft outer hull) can inhibit germination (6), and the endocarp can reduce the rate of imbibition (3); removal or careful scarification of these covering structures can promote germination (3,4,6,10,11,12,13,14), but removal of the endocarp can also damage seeds, reducing the proportion which germinates (2). Warm stratification (6,9), pre-soaking (1,2,6,7,14), or pre-chilling treatments (1,5,7,10,12) can be promotory, but soaking for more than 21 days reduces germination (1). Treatment with gibberellins can be promotory, particularly where the seeds have first been scarified (1,2,4). A 10 minute scarification treatment with concentrated sulphuric acid appears to be safe and can be combined with advantage with subsequent gibberellin or pre-chilling treatments (12).
It is suggested that dormant seeds of Pistacia spp. be pre-treated as follows before the germination test. Scarify the seed: either by hand, by first removing the epicarp and then chipping the endocarp or rubbing it with sandpaper, or by a 10 minute treatment in concentrated sulphuric acid followed by through rinsing in running water. Then pre-treat the seeds with GA3 at 500-1000 ppm for 24 hours, followed by a 2 to 4 week pre-chill at 3°-5°C. Test the seeds for germination as already described for non-dormant seeds: the test duration should be at least 6 weeks (2).
VII. References
1. Ayfer, M. and Serr, E.F. (1961). Effects of gibberellin and other factors on seed germination and early growth in Pistacia species. Proceedings of the American Society for Horticultural Science, 77, 308-315.
2. Casini, E. and Conticini, L. (1979). [The germinability of seeds of Pistacia vera and Pistacia terebinthus.] Rivista di Agricoltura Subtropicale e Tropicale, 73, 233-240.
3. Crane, J.C. and Forde, H.I. (1974). Improved Pistacia seed germination. California Agriculture, 28, 8-9.
4. Dahab, A.M.A., Shafiq, Y. and Al-Kinany, A. (1975). Effects of gibberellic acid, B-nine and scarification on the germination of seeds of Pistacia khinjuk Stock. Mesopotamia Journal of Agriculture, 10, 13-19.
5. Hartmann, H.T. (1967). Effects of various treatments on seed germination of several tree species. Plant Propagator, 12, 10-12.
6. Joley, L.E. (1960). Experiences with propagation of the genus Pistacia. Proceedings of the Plant Propagators' Society, 10, 287-292.
7. Joley, L.E. and Opitz, K.W. (1971). Further experiences with propagation of Pistacia. Combined Proceedings of the International Plant Propagators' Society, 21, 67-76.
8. Kravchenko, V.I. (1961). [The effect of the duration of pistachio seed storage on their germinating power in the ground.] Izvest. Akad. Nauk Turkmen SSR Ser. Biol. Nauk, 5, 83-87. (From Biological Abstracts, 1963, 42, 7667.)
9. Lemaistre, J. (1959). Le pistachier. Etude bibliographique. Fruits, 2, 57-77.
10. Maggs, D.H. (1973). The pistachio as an Australian crop. Journal of the Australian Institute of Agricultural Science, 39, 10-17.
11. Nimadzhanova, K.N., Abdurakhmanov, N.A. and Rafieva, M.G. (1977). [The effect of seed covers on the germination of some nut crops.] Subtropicheskie Kul'tury, 1/2, 129-132. (From Horticultural Abstracts, 1978, 48, 7017.)
12. Shafiq, Y. and Kettaneh, M.S. (1971). The effect of stratification, sulphuric acid and combination treatments on germination percentage of seeds of wild pistacia (Pistacia khinjuk). Mesopotamia Journal of Agriculture, 7, 37-43.
13. Sheikh, M.I. (1979). Tree seeds respond to acid scarification. Pakistan Journal of Forestry, 29, 253-254.
14. Whitehouse, W.E. (1957). The pistachio nut. A new crop for the Western United States. Economic Botany, 11, 281-321.
15. Riley, J.M. (1981). Growing rare fruit from seed. California Rare Fruit Growers Yearbook, 13, 1-47.
