CHAPTER 31. CONVOLVULACEAE

The Convolvulaceae comprise roughly 1000 species of shrubs and herbaceous plants in about 50 genera. The most important genus is Ipomoea which provides edible roots (Ipomoea batatas (L.) Lam., sweet potato), leaf vegetables (e.g. Ipomoea eriocarpa R. Br.) and fodder (e.g. Ipomoea pes-caprae (L.) Sweet). The seeds show orthodox storage behaviour.

SEED DORMANCY AND GERMINATION

The major problem in seed germination tests of the Convolvulaceae is the presence of the seed coat which can delay or prevent imbibition: that is, hardseededness is a common problem. The seeds are non-endospermic, and 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 scarification and chipping treatments are useful in promoting germination. Detailed information on seed dormancy and germination is provided in this chapter for the genus Ipomoea and Table 31.1 provides a summary of germination test procedures and dormancy-breaking treatments for species in other genera. In addition the algorithm below may be helpful in developing germination test procedures for other species.

RBG Kew Wakehurst Place algorithm

The first step in the algorithm is to test several samples of seeds at constant temperatures of 11° to 26°C with light applied for 12h/d. Four constant temperature regimes at 5°C intervals are suggested.

If none of these constant temperature regimes is successful in promoting full germination then the second step of the algorithm is to pre-chill a further sample of seeds at 2° to 6°C for 8w and then test for germination in the most successful germination test regime determined in step one.

If the second step of the algorithm does not result in full germination then the third step is to chip a further sample of seeds and then test in the most successful regime determined in steps one and two. This may include a pre-chill treatment if the second step of the algorithm results in an appreciable increase in germination compared to step one.

TABLE 31.1 Summary of germination test recommendations for species within the Convolvulaceae

Species and Authority	Substrate	Temperature	Duration	Additional directions	Source
Convolvulus arvensis L.	TP; BP; S	20°/30°C	7d	scarify, concentrated sulphuric acid, 1h, rinse	Everson
				scarify, absolute alcohol, 20h, or file	Atwater
Convolvulus lanatus Vahl.				scarify, sulphuric acid, 30 min, or percussion, shake, 4h	Atwater
Convolvulus tricolor L.	TP; BP	20°/30°C; 20°C	14d	pierce, chip or file cotyledon end of testa	ISTA
		20°/30°C	14d	clip hard seeds	Atwater
Dichondra repens Forst. & G. Forst.	TP	20°/30°C	21d		ISTA
	BP	20°/30°C	28d	continue test for a further 5d if (reversible) hard seeds have begun to imbibe	AOSA
Pharbitis purpurea (Roth) Bojer	TP; BP; S	20°/30°C; 20°C	21d	pierce, chip or file cotyledon end of testa	ISTA
Quamoclit vulgaris Choisy	TP; BP; S	20°/30°C; 20°C	21d	pierce, chip or file cotyledon end of testa	ISTA

IPOMOEA

I. alba L.	moon flower
I. aquatica Forsk. [I. reptans Poir.]	water convolvulus, water spinach, kangkong
I. arborescence Don
I. batatas (L.) Lam. [Convolvulus batatas L.]	sweet potato
I. bederacea (L.) Jacq. var bederacea	ivyleaf morning glory
I. bederacea (L.) Jacq. var intergriuscula Gray	entireleaf morning glory
I. coccinea L.	scarlet morning glory
I. heptophylla (Rottb. & Willd.) Voigt	palmleaf morning glory
I. lacunosa L.	pitted or white morning glory
I. noctiflora L.
I. obscura Hassk.
I. purpurea Lam. [Convolvulus purpureus L.; Convolvulus major Hort.; Pharbitis purpurea Voigt]	common or tall morning glory
I. quamoclit L.	cypress vine
I. sinensis
I. trichocarpa Ell.
I. tricolor Cav. [I. rubro-caerulea Hook.; Pharbitis rubro-caerulea (Hook.) Choisy]
I. wrightii Gray	willow leaf morning glory

I. Evidence of dormancy

Whilst the production of viable seeds from sweet potato (I. batatas) clones - particularly those subject to repeated vegetative propagation - is difficult, e.g. (17,18,24), seed viability can be maintained in the long-term with, for example, no appreciable loss in viability over a 20 year period (13-15). Moreover, no problems have been encountered when raising plants from seeds in long-term storage (19,29).

Embryos extracted from sweet potato seeds have been reported to be non-dormant (4). However, seed germination can be severely restricted by hardseededness (1,4,13,15,21,23,24,26,28,30). Reported proportions of hard seeds in seed populations vary from around 50% (20,21) to 90 or 95% (23,28). The germination of seeds of other Ipomoea spp. can also be restricted by hardseededness (3,5-9,22,25,27). As far as possible the information is presented below according to species, but this has not been possible in all cases.

II. Germination regimes for non-dormant seeds

I. alba

BP: 20°/30°C (16h/8h): 21d (AOSA)

I. aquatica

BP; S: 30°C: 10d (ISTA)

I. noctiflora

BP; TP; S: 20°/30°C (16h/8h); 20°C: 21d (ISTA)

I. quamoclit

BP: 20°/30°C (16h/8h): 14d (AOSA)

I. tricolor

BP; TP; S: 20°/30°C (16h/8h); 20°C: 21d (ISTA)

Ipomoea spp.

BP: 20°/30°C (16h/8h); 20°C: 14d (AOSA)

III. Unsuccessful dormancy-breaking treatments

I. batatas

Scarification: sulphuric acid, 50%, 2,7,10 min (26); concentrated sulphuric acid, 2,5 min (26); mechanical, crack outer seedcoat with pliers (26)

I. bederacea var bederacea

Constant temperatures: 40°C (6)

Alternating temperatures: 15°/10°C (day/night) (27)

Light: to intact seeds (27)

I. coccinea

Scarification: concentrated sulphuric acid, 60 min, germinate at 5°C, 45°C, 50°C (7,9)

I. lacunosa

Constant temperatures: 40°C (6)

I. obscura

Scarification: concentrated sulphuric acid, 60 min, germinate at 5°C, 45°C, 50°C (8)

I. purpurea

Abscisic acid: co-applied, 10^-3 M (10)

Naphthaleneacetic acid: co-applied, 10^-2 -10^-7 M (10)

Mannitol: co-applied, 3x10^-1 M (11)

Light: far red, 4h, 23°C (11)

IV. Partly-successful dormancy-breaking treatments

I. aquatica

Alternating temperatures: 30°/25°C, 25°/20°C (day/night) on top of filter papers (12); 20°/15°C, 15°/13°C (day/night) on top of filter papers or in soil (12)

I. arborescence

Scarification: concentrated sulphuric acid, 3-15 min (22)

I. batatas

Scarification: concentrated sulphuric acid, 20-60 min (1,30); concentrated sulphuric acid, 10 min (26,28); sulphuric acid, 50%, 20 min (26); concentrated sulphuric acid, 15-60 min (20); rub, 3-4 min, medium emery cloth (26); emery paper (23).

I. bederacea var bederacea

Constant temperatures: 20°C, 25°C, 30°C, 40°C, scarified seeds, concentrated sulphuric acid, 1h (6)

Alternating temperatues: 20°/30°C (16h/8h), intact seeds (6); 20°/30°C (12h/12h), scarified seeds, concentrated sulphuric acid, 1h (6); 32°/27°C (day/night), scarified seeds (27)

Light: at 32°/27°C (day/night), scarified seeds (27)

I. bederacea var intergriuscula

Alternating temperatures: 20°/30°C (16h/8h), intact seeds (6)

Scarification: concentrated sulphuric acid, 30 min, germinate at 16°C (3); concentrated sulphuric acid, 60 min, germinate at 40°C (6)

I. coccinea

Scarification: concentrated sulphuric acid, 30-105 min (7); concentrated sulphuric acid, 30-120 min (9); concentrated sulphuric acid, 60 min, germinate at 10°-40°C (9)

I. heptophylla

Scarification: concentrated sulphuric acid, 30,45 min (7)

I. lacunosa

Alternating temperatures: 20°/30°C (16h/8h), intact seeds (6)

Scarification: concentrated sulphuric acid, 30 min (7)

I. obscura

Scarification: concentrated sulphuric acid, 30 min, germinate at 10°-40°C (8); concentrated sulphuric acid, 60 min, germinate at 10°C, 40°C (8)

I. purpurea

Constant temperatures: 15°C, 35°C (2)

Light: fluorescent, at 23°C (11); red, 1,2h (11); infra red, 5s (10)

CA₃: co-applied, 10^-4 M (10, 11)

Thiourea: co-applied, 10^-4 M (10)

Kinetin: co-applied, 10^-4 M (10)

Mannitol: co-applied, 3x10^-1 M, at 23°C in red or white light (11)

I. sinensis

Alternating temperatures: 14.5°/28°C (night/day) in light or dark (5)

I. trichocarpa, I. wrightii

Scarification: concentrated sulphuric acid, 30 min, germinate at 16°C (3)

Ipomoea spp.

Scarification: mechanical (25)

V. Successful dormancy-breaking treatments

I. aquatica

Alternating temperatures: 25°/20°C, 30°/25°C (day/night) in soil (12); 30°/25°C, 25°/20°C (day/night) on top of filter papers (12)

I. batatas

Scarification: concentrated sulphuric acid (4, 14); concentrated sulphuric acid, 45 min (20,24); concentrated sulphuric acid, 20 min (26); concentrated sulphuric acid, 20 min, germinate at 30°C, then prick seedcoats of non-imbibed seeds (15); mechanical (4); emery wheel, 1750 rpm (20)

Removal of seed covering structures: part of seed cost (23); clip (24); file (26)

I. bederacea var bederacea

Alternating temperatures: 20°/30°C (16h/8h), then prick non-germinated seeds (6)

Scarification: concentrated sulphuric acid, 30 min, germinate at 16°-32°C (3); concentrated sulphuric acid, 1h, germinate at 35°C (6)

I. bederacea var intergriuscula

Alternating temperatures: 20°/30°C (16h/8h), then prick non-germinated seeds (6)

Scarification: concentrated sulphuric acid, 30 min, germinate at 16°-32°C (3); concentrated sulphuric acid, 1h, germinate at 20°/30°C (12h/12h), 20°C, 25°C, 30°C, 35°C (6)

I. coccinea

Scarification: concentrated sulphuric acid, 3h (9); concentrated sulphuric acid 4,6h (7)

Removal of seed covering structures: prick (7,9)

I. heptophylla

Scarification: concentrated sulphuric acid, 1-6h (7) Removal of seed covering structures: prick (7)

I. lacunosa

Alternating temperatures: 20°/30°C (16h/8h), then prick non-germinated seeds (6)

Scarification: concentrated sulphuric acid, 30 min, germinate at 16°-32°C (3); concentrated sulphuric acid, 1h, germinate at 20°/30°C (12/12h), or 20°-40°C (6); concentrated sulphuric acid, 45 min-6h (7)

Removal of seed covering structures: prick (7)

I. noctiflora

Pierce, chip or file off fragment of testa (ISTA)

I. obscura

Scarification: concentrated sulphuric acid, 45-180 min (8); concentrated sulphuric acid, 60 min, germinate at 15°-35°C (8) Removal of seed covering structures: prick (8)

I. purpurea

Pierce, chip or file off fragment of testa (ISTA)

Constant temperatures: 20°-30°C (2)

Scarification: concentrated sulphuric acid, 30 min, germinate at 16°-32°C (3)

Pre-soak: 70°C, 10 min (10)

Ultrasonics: 20 kc/s, 2 min (10)

I. quamoclit

Pierce, chip or file off fragment of testa (ISTA)

Scarification: concentrated sulphuric acid, 30 min, germinate at 16°-32°C (3)

I. trichocarpa

Scarification: concentrated sulphuric acid, 30 min, germinate at 16°-32°C (3)

I. tricolor

Pierce, chip or file off fragment of testa (ISTA)

I. wrightii

Scarification: concentrated sulphuric acid, 30 min, germinate at 16°-32°C (3)

VI. Comment

Imbibed seeds of Ipomoea spp. will germinate over a wide range of constant and alternating temperatures: those prescribed by ISTA/AOSA are suitable, and there may be some advantage in testing in the alternating temperature regime 20°/30°C (16h/8h) since this may help in removing hardseededness. Germination can be promoted by light (11,12,27), and thus it is recommended that light be applied to germination tests. Mechanical methods of removing hardseededness are preferred. For germination tests it is probably simplest to prick, with a needle, the seed coats of all impermeable seeds remaining after 4 or 5 days in test. If some form of acid scarification is deemed essential, e.g. for field sowings, then a 10 minute treatment with concentrated sulphuric acid is suggested. This is unlikely to render all seeds permeable (26,28), but longer treatments may be damaging to some seeds (20).

VII. References

1. Abramides, E., Pereira, A.S. and Monteiro, D.A. (1977). [Scarification of seeds of sweet potato (Ipomoea batatas (L.) Lam.) with sulphuric acid.] Ciencia e Cultura, 29, 7. (From Seed Abstracts, 1978, 1, 1983.)

2. Cole, A.W. and Coats, G.E. (1973). Tall morning glory germination response to herbicides and temperature. Weed Science, 21, 443-446.

3. Crowley, R.H. and Buchanan, G.A. (1980). Responses of Ipomoea spp. and smallflower morning glory (Jacquemontia tamnifolia) to temperature and osmotic stresses. Weed Science, 28, 76-82.

4. Edmond, J.B. and Ammerman, G.R. (1971). Sweet potatoes: production, processing, marketing, 26 pp. The AVI Publishing Company Inc., Westport, Connecticut.

5. Fenner, M. (1980). Germination tests on thirty-two East African weed species. Weed Research, 20, 135-138.

6. Gomes, L.F., Chandler, J.M. and Vaughan, C.E. (1978). Aspects of germination, emergence, and seed production of three Ipomoea taxa. Weed Science, 26, 245-248.

7. Hardcastle, W.S. (1978). Enhancement of Ipomoea seed germination. Proceedings of the 31st Annual Meeting of the Southern Weed Science Society, 280-281.

8. Hardcastle, W.S. (1978). The influence of temperature and acid scarification duration on Ipomoea obscura Hassk. seed germination. Weed Research, 18, 89-91.

9. Hardcastle, W.S. (1978). Influence of temperature and acid scarification duration on scarlet morning glory (Ipomoea coccinea) seed germination. Weed Science, 26, 261-263.

10. Holm, R.E. and Miller, M.R. (1972). Weed seed germination responses to chemical and physical treatments. Weed Science, 20, 150-153.

11. Holm, R.E. and Miller, M.R. (1972). Hormonal control of weed seed germination. Weed Science, 20, 209-211.

12. Huang, H. (1981). [Effects of temperature on germination, growth and dry matter contents of two tropical vegetable with high nutritive value - edible amaranth and water convolvulus.] Memoirs of the College of Agriculture, National Taiwan University, 21, 88-105.

13. Jones, A. (1980). Sweet potato. In Hybridization of Crop Plants (eds. W.R. Fehr and H.H.adley), pp. 645-655. American Society of Agronomy Inc., Madison, Wisconsin.

14. Jones, A. and Dukes, P.D. (1981). Viability of stored sweet potato seed. HortScience, 16, 287-288.

15. Jones, A. and Dukes, P.D. (1982). Longevity of stored seed of sweet potato. HortScience, 17, 756-757.

16. Jones, A., Dukes, P.D. and Cuthbert, F.D. Jr. (1977). Pesticides increase true seed production of sweet potato. HortScience, 12, 165-167.

17. Jones, A. and Jackson, C.R. (1968). Fungi from floral parts of sweet potato (Ipomoea batatas (L.) Lam.). HortScience, 3, 76-77.

18. Martin, F.W. and Cabanillas, E. (1966). Post-pollen-germination barriers to seed set in sweet potato. Euphytica, 15, 404-411.

19. Martin, F.W. and Jones, A. (1971). Flowering and fertility changes in six generations of open pollinated sweet potatoes. Journal of the American Society for Horticultural Science, 96, 493-495.

20. Martin, J.A. Jr. (1946). Germination of sweet potato seed as affected by methods of scarification. Proceedings of the American Society for Horticultural Science, 47, 387-390.

21. Miller, J.C. (1937). Inducing the sweet potato to bloom and set seed. Journal of Heredity, 28, 347-349.

22. Nalawadi, U.G., Elengovan, R., Gowda, J.V.N. and Sulladmath, U.V. (1978). Acid scarification improves germination in Ipomoea arborescens Don. Current Research, 7, 104.

23. Nunes, W. De O. (1968). [Improvement of sweet potato. 2. Harvest of fruit and germination of seed.] Pesquisa Agropecuaria Brasileira, 3, 263-266.

24. Purseglove, J.W. (1968). Convulvulaceae. In Tropical Crops. Dicotyledons, pp. 78-88. Longmans, London.

25. Rose, D.H. (1915). A study of delayed germination in economic seeds. Botanical Gazette, 59, 425-444.

26. Steinbauer, C.E. (1937). Methods of scarifying sweet potato seed. Proceedings of the American Society for Horticultural Science, 35, 706-608.

27. Thullen, R.J. and Keeley, P.E. (1982). The effects of some environmental conditions on the germination of black nightshade and ivyleaf morning glory. Proceedings of the Western Society of Weed Science, 35, 76-82.

28. Venkataratnam, L. and Satyanarayanamurthy, K. (1953). A simple method of germinating sweet potato seeds. Current Science, 22, 29.

29. Yen, D.E. (1974). The sweet potato and Oceania, pp. 235-237. Bishop Museum Press, Honolulu, Hawaii, Bulletin 236.

30. Monteiro, D.A., Castro, J.L. and Abramides, E. (1977). [Scarification of sweet potato seeds in concentrated sulphuric acid.] Instituto Agronomico (Sáo Paulo), Boletim Técnico, No. 42, 6 pp.