The Sapindaceae comprise more than 1000 species of trees, shrubs and, rarely, herbaceous plants within about 125 genera which provide edible fruits (e.g. Blighia sapida Koenig, akee), beverages (e.g. Paullinia cupana HBK, guarana) and oils (Schleichera oleosa (Lour.) Merr., lac tree). The fruits are diverse: the edible portion of fruits such as akee and litchi (Litchi chinensis Sonn.) is the aril which surrounds the seed. Seed storage behaviour may be variable; further investigations are required. Some species are known to show orthodox seed storage behaviour - for example, Koelreuteria paniculata Laxm. is maintained in the long-term seed store at the Wakehurst Place Gene Bank. But the species with edible fruits such as Euphoria longan Steud., Litchi chinensis Sonn., and Nephelium spp. are thought to show recalcitrant seed storage behaviour.
SEED DORMANCY AND GERMINATION
Germination and seedling development can be comparatively slow, and the seed coats may delay germination. B.R. Atwater classifies seed morphology as non-endospermic seeds with axile foliar embryos within hard seed coats (see Table 17.2, Chapter 17). Table 65.1 provides a brief summary of information on suitable germination test procedures and dormancy-breaking treatments. In addition the algorithm below may be helpful in developing suitable germination test procedures.
RBG Kew Wakehurst Place algorithm
It is obligatory to chip the seed coats of all seeds prior to testing for germination in this algorithm.
The first step in the algorithm is to test samples of the chipped seeds at constant temperatures between 6°C and 36°C with light applied for 12h/d. Where sufficient seeds are available it is suggested that seven constant temperature regimes (6° to 36°C in 5°C steps) be used in this first step. If this is not possible then test in four constant temperature regimes (6° to 36°C in 10°C steps). In the latter case if full germination is not achieved but the results suggest a trend in germination response to constant temperatures then test a further sample of chipped seeds at the most appropriate intermediate constant temperature. For example, if the proportions of seeds germinating at 26°C and 36°C are similar but greater than for the lower constant temperatures then test a further sample of chipped seeds at a constant temperature of 31°C with light applied for 12h/d.
If full germination does not occur in the above constant temperature regimes then the second step in the algorithm is to test two further samples of chipped seeds in alternating temperature regimes of 23°/9°C (12h/12h) and 33°/19°C (12h/12h) with light applied for 12h/d during the period spent at the upper temperature.
If full germination does not occur in the second step of the algorithm 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 chipped seeds in the most appropriate temperature regime determined from a comparison of the results of steps one and two.
TABLE 65.1 Summary of germination test recommendations for species within the Sapindaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Blighia sapida Koenig |
|
|
21d |
warm stratification |
Riley |
|
Cardiospermum halicacabum L.
|
BP |
20°/30°C |
10d |
clip seed coat |
AOSA |
|
|
20°/30°C |
28d |
|
Atwater |
|
|
Euphoria longan Steud.
|
S |
25°-30°C |
17d |
light, continuous |
CHML |
|
|
|
30d |
warm stratification |
Riley |
|
|
Litchi chinensis Sonn. |
S |
25°-30°C |
16d |
light, continuous |
CHML |
|
|
|
30d |
warm stratification |
Riley |
|
|
BP |
25°C; 30°C; 35°/20°C; |
63d |
scarify |
A |
|
|
|
20°/30°-35°C |
|
|
|
|
|
Melicoccus bijugatus L. |
|
|
21d |
pre-soak, 24h |
Riley |
|
Nephelium lappaceum L. |
S |
25°-30°C |
14d |
light, continuous |
CHML |
|
Nephelium malaiense |
S |
25°-30°C |
16d |
light, continuous |
CHML |
|
Pometia pinnata Forst. & G. Forst. |
|
|
21d |
warm stratification |
Riley |
