FACTORS LIMITING SEED GERMINATION IN Scyphiphora hydrophyllacea GAERTN f. AND Pempilis acidula J R & FORST

Abstract

Scyphiphora hydrophyllacea is a highly threatened true mangrove confined to JafTna and asingle locality in Kalpitiya (Trimen 1974; Dassanayake and Clayton 1998). Pemphisacidula is restricted to small pockets in few coastal areas. Both produce fruits and seedsnevertheless, seedlings were not observed in their natural habitats. Factors governing seedgermination in these two species were studied. For all experiments, randomly collected ripe.seed samples were used within two weeks of collection. Moist filter paper method was usedand daily observations were recorded.

In P. acidula, seed production was 100%. Percentage of fruit bearing seeds was 10% in S.hydrophyllacea, but none of them gave rise to healthy seedlings. Seed germination of bothspecies was 0% in water collected from respective natural habitats. In P. acidula%germination was 35% in 75% and 40% in 87.5% dilution of water from natural habitat.In distilled water, 65% of the seeds germinated. Continuous washing of seeds in runningtap water increased percentage germination to 75%.

Dormancy breaking treatments such as heat treatment, seed nicking, acid base treatment,cold treatment and treatment with gibberellic acid did not increase germination abovenormal 65% value.

Exposure to natural light, photoperiod and oxygen level also affected seed germination.Analysis of data consisted of ANa VA at 5% level of significance using Minitab package.In P. acidula, salinity of soil water (up to 34 ppt) and salt deposits on seed coat seem to bemajor causes hindering seed germination in natural habitat. Seeds buried ill sand may alsonot receive adequate amount of light (Isikawa 1962; Fujii 1962). Oxygen concentrationmay 1I0tbe enough when the ground is covered with water during tides. Lack of seedlingsmay therefore be due to lack of seed germination under natural conditions.

In S. hydrophyllacea, very low percentage of seed bearing fruits and inability to producehealthy seedlings explain why it has become highly threatened. Production of large numberof seedless fruits and inability to produce normal seedlings could be due to genetic disorderin seeds, which is a very common phenomenon known as inbreeding depression inisolated, small populations.

Presence of self-sterility and the absence of pollinator niight be some other reasons. Hence,studies on the possibility of propagating S. hydrophyllacea by vegetative means areurgently needed to conserve this highly threatened tree species.