The Passifloraceae comprise more than 500 species of herbaceous or woody plants within 12 genera which provide edible fruits (e.g. Passiflora edulis Sims, passion fruit). The fruits are capsules or berries and the seeds show orthodox storage behaviour.
SEED DORMANCY AND GERMINATION
The seeds have a fleshy aril (an outer covering of the seed attached to the funiculus, see Chapter 3, Volume I) and may show considerable dormancy. B.R. Atwater classifies seed morphology as non-endospermic seeds with axile foliar embryos within woody seed coats and an inner semi-permeable layer (see Table 17.2, Chapter 17). Treatments to the seed covering structures and alternating temperatures tend to promote germination.
Detailed information on seed germination procedures and dormancy-breaking treatments are provided for the genus Passiflora in this chapter. 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 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 the above regime does not promote full germination then the second step in the algorithm is to co-apply 7 x 10-4 M GA3 in the germination test substrate and test a fresh sample of seeds in the alternating temperature regime specified in step one.
PASSIFLORA
|
P. edulis Sims |
passion fruit, granadilla |
|
P. ligularis Juss. |
sweet grandilla |
|
P. maliformis |
|
|
P. quadrangularis L. |
giant granadilla |
I. Evidence of dormancy
Difficulties in the germination of seeds of the above orthodox species (1) can occur as a result of seed dormancy (3).
II. Germination regimes for non-dormant seeds
P. edulis
Alternating temperatures: 20°/30°C (16h/8h), 6w (5)
III. Unsuccessful dormancy-breaking treatments
P. edulis
Constant temperatures: 20°C, 30°C (3)
GA3: co-applied (3)
Pre-soak: 24h (3)
Cytase: (3)
IV. Partly-successful dormancy-breaking treatments
P. edulis
Alternating temperatures: 20°/30°C (12h/12h) (3)
Scarification: sand paper (3); sulphuric acid, 75%, 6h (3)
Removal of seed covering structures: chip (3); crack seed coats (3); crack, seed coats, germinate at 20°/30°C (12h/12h) (3); crack seed coats, then GA3, co-applied (3)
P. ligularis
Scarification: sandpaper, germinate at 20°/30°C (12h/12h) (3)
P. maliformis
Constant temperatures: 30°C (3)
Alternating temperatures: 20°/30°C (12h/12h) (3)
V. Successful dormancy-breaking treatments
P. edulis
Scarification: file (2); sandpaper (2)
Passiflora spp.
Pre-soak: 24h (4)
VI. Comment
The germination of dormant seeds of Passiflora spp. requires scarification and alternating temperatures (3). It is suggested that the seeds be scarified with sand paper and then tested for germination on top of filter papers at an alternating temperature of 20°/30°C (16h/8h) for 6 weeks.
VII. References
1. Costa, C.F. Da, Oliveira, E.L.P.G. De and Lellis, W.T. (1974). [Persistence of the germinating capacity of passion fruit seeds.] Boletim do Instituto Biológico da Bahia, 13, 76-84. (From Horticultural Abstracts, 1976, 46, 649.)
2. Kuhne, F.A. (1968). Cultivation of granadillas. Farming in South Africa, 43, 29-32.
3. Morley-Bunker, M.J.S. (1980). Seed coat dormancy in Passiflora species. Annual Journal of the Royal New Zealand Institute of Horticulture, 8, 72-84.
4. Riley, J.M. (1981). Growing rare fruit from seed. California Rare Fruit Growers Yearbook, 13, 1-47.
5. Thai, T.Y. (1977). Storage of passion fruit (Passiflora edulis forma flavicarpa) seeds. Malaysian Agricultural Journal, 51, 118-123.
