The Punicaceae comprise several species of trees and shrubs within the genus Punica. Punica granatum L., pomegranate, provides an edible fruit, and the roots, fruit rind and seeds have medicinal uses. The fruit is a berry containing numerous seeds surrounded by a juicy pulp. Seed storage behaviour is orthodox (see below).
SEED DORMANCY, GERMINATION AND STORAGE
The only reference we have found to the germination and storage behaviour of seeds within the Punicaceae is Riley (1981) for Punica granatum L. There it is suggested that the seeds should be dried to 70% of their harvest weight and stored at 4° to 5°C. Under these storage conditions it is suggested that the seeds will have a storage life of 3 years and germinate within 14 to 30 days of sowing if they are pre-chilled at 1° to 5°C for between 30 and 60 days (Riley, 1981). Since no recommended germination test procedures are available for pomegranate we investigated the germination response of a single seed lot to a limited number of constant and alternating temperature germination test regimes. The results are described and discussed below.
Seeds were extracted by hand from fruits purchased locally, rinsed in water several times, blotted surface dry and then dried over silica gel (changed daily) at 20°C for 10 days. Seed moisture contents before and after drying were 76.5 and 4.8% (fresh weight basis) respectively. Initial germination (normal) of the fresh seeds when extracted and tested between moist rolled paper towels at 20°/30°C (16h/8h) for 42 days was 87%. A further test after drying (test details as above) recorded 88% normal germination.
The dried seeds were hermetically stored in a deep freeze maintained at -20°C. After 3 weeks in storage 2000 seeds were removed. Ten groups of 200 seeds each were tested for germination in one of each of the following regimes: constant temperatures of 10°C, 15°C, 20°C, 25°C, 30°C, or 35°C; alternating temperatures (all 16h/8h) of 15°/30°C, 20°/30°C, or 20°/35°C; or 3° to 5°C for 7 days (that is pre-chilling) then 20°/30°C (16h/8h). In all cases the seeds received a brief daily exposure to diffuse indoor light. The tests were concluded after 21 days. Since the highest germination was observed in the 20°/35°C alternating temperature regime all the seeds which had failed to germinate within 21 days in the original test environment were transferred to this alternating temperature regime for a further 14 days. Cumulative normal germination after various periods in test are shown in Table 61.1.
The pomegranate seeds germinated most rapidly at constant temperatures of 30° and 35°C (Table 61.1); at 35°C initial germination was slightly more rapid, but the seedlings were not vigorous and fungi developed on several seeds tested in this regime (whereas in other regimes no such problems occurred). Pre-chilling for 7 days was not advantageous (compared to 20°/35°C throughout), but the seeds were not killed by exposure to the lower temperatures. For example, no seeds germinated when tested at 10°C for 21 days, but 93% germinated when subsequently transferred to 20°/35°C (Table 61.1). Of the regimes investigated, it is clear that an alternating temperature regime of 20°/35°C (16h/8h) is the most suitable (at least for this lot) for germination tests of Punica granatum. In this regime no more seeds germinated after 28 days in test.
Clearly the seeds show orthodox seed storage behaviour since they were neither killed by desiccation to 5% moisture content nor by exposure to sub-zero temperatures (-20°C) (once dried). On the basis of these results, it is suggested that seeds of Punica granatum be tested for germination between moist paper in an alternating temperature regime of 20°/35°C (16h/8h) for a minimum of 28 days.
Reference
Riley, J.M. (1981). Growing rare fruit from seed. California Rare Fruit Growers Yearbook, 13, 1-47.
Table 61.1 Germination (normal) or seeds (200 per test) of Punica granatum L. in various constant and alternating temperature test regimes.
|
Initial Test |
Cumulative normal germination, % |
|||
|
Days in initial test environment |
After a further |
|||
|
Environment |
|
|
|
14 days at |
|
|
7 |
14 |
21 |
20°/35°C |
|
10°C |
0 |
0 |
0 |
93 |
|
15°C |
0 |
0 |
0 |
96 |
|
20°C |
0 |
2 |
39 |
91 |
|
25°C |
0 |
23 |
53 |
88 |
|
30°C |
20 |
83 |
84 |
84 |
|
35°C |
25 |
81 |
83 |
84 |
|
15°/30°C |
0 |
10 |
46 |
95 |
|
20°/30°C |
0 |
63 |
85 |
90 |
|
20°/30°C* |
0 |
75 |
|
91 |
|
20°/35°C |
0 |
73 |
94 |
95 |
* After pre-chilling for 7 days at 3°-5°C; subsequently moved to 20°/35°C after 14d at 20°/30°C
