Seed Dormancy and Germination Requirements of Two Endemic Palm Species of Sri Lanka

Sri Lankan endemic lowland rain forest palm species Areca concinna and Oncosperma fasciculatum are considered to be threatened due to habitat loss. Seed dormancy and germination behavior of these species are poorly understood. Therefore, the present study was conducted to identify the dormancy, germination requirements and the effect of storage time on dormancy alleviation of these species. Ripe fruits of A. concinna and O. fasciculatum were collected from home-gardens and natural populations. Initial moisture contents of fruits were measured. The effects of different gibberellic acid (GA3) concentrations (0, 250, 500, 1000, 2000, 3000 and 4000 ppm) and the removal of fruit coats and/or operculum on seed germination of both species were tested in vitro. The effects of wet storage (moist coir dust in sealed bags) at 250 C and dry storage (open trays) at ambient room temperature (approx. 29º C) on seed dormancy break and seed viability were tested after 0, 3, 9 and 12 months. Fruit moisture of A. concinna and O. fasciculatum were approximately 15% and 30%, respectively. Intact fruits of A. concinna treated with 500 ppm GA3, showed a significantly higher germination percentage (88%) than 0 ppm (33%) (P<0.05).Intact fruits of O. fasciculatum did not respond to GA3 treatments, with <4% germination. The highest germination percentages were achieved by removing pericarp+mesocarp+endocarp and 1000 ppm GA3 application in A. concinna (89%), and removing pericarp+mesocarp and operculum in O. fasciculatum (36%). Seed viability of fresh A. concinna was 87% and remained high even after 12 months of dry storage while that of O. fasciculatum has declined to 2% from 85% after 6 months of dry storage. Seed germination percentages of intact A. concinna and O. fasciculatum after 12 months of dry storage were 20% and 0% respectively. Seeds of A. concinna stored wet at 25ºC germinated slowly during 12 month period reaching 22%. Seeds of O. fasciculatum showed a similar pattern reaching 36%. It can be concluded that both species exhibit physiological dormancy. O. fasciculatum was identified as recalcitrant while A. concinnaas orthodox. Seed germination of A. concinna can be promoted by removing all fruit coats and GA3 treatment whereas in O. fasciculatum by removing the operculumor storing seeds in moist coir dust for >6 months. These findings will be useful in producing seedlings for restoration of these species.Keywords: Areca, Oncosperma, Orthodox, Physiological dormancy, Recalcitran

Species-specific smoke effects on seed germination of plants from different habitats from Sri Lanka

Smoke and in particular karrikinolide (KAR1), a growth promoting compound found in smoke, have been shown to enhance seed germination in phylogenetically diverse plant families from both fire-prone and fire-free ecosystems. We tested the effects of water saturated with smoke, “smoke water” (SW), and KAR1 on seed germination of 18 native and exotic plant species from different habitats affected by anthropogenic fires in Sri Lanka. Seeds were tested with five concentrations of SW (5 %, 25 %, 50 %, 75 %, 100 %) and those that positively responded were tested with three different concentrations of KAR1 (10 nM, 100 nM and 1 μM). Germination percentage of three native (Flueggea leucopyrus, Maesa indica and Phyllanthus emblica) and two exotic (Chromolaena odorata and Hyptis suaveolens) species was significantly increased by both SW and KAR1 treatments. Seed germination percentage of the exotic species Euphorbia heterophylla was increased by SW treatments only. The time taken for 50 % germination (t50) of C. odorata, M. indica and P. emblica was decreased by both SW and KAR1, whilst t50 of E. heterophylla was decreased by SW only. Species-specific seed germination promotion response to SW and KAR1 was observed in both native and exotic plant species tested in the study confirming that the recruitment ecology of at least some species found in fire prone habitats of Sri Lanka is likely to be influenced by fire management practices

Seed Biology of Ten Common Roadside Sri Lankan Weed Species

Weeds are undesirable in habitats where they grow and cause negative economic and environmental impacts. Understanding in weed seed germination is important to deploy control measures. This study was conducted to evaluate the effect of seed dormancy, smoke, KAR1, salinity and pH on germination of ten common roadside weed species in Sri Lanka. Freshly collected seeds of ten weed species were subjected to five treatments vis, (1) 0 and 500 ppm GA3; (2) Smoke solutions of 0%, 5%, 25%, 50%, 75%, and 100% strength; (3) 0 nM, 10 nM, 100 nM and 1 μM KAR1 solutions; (4) 0 nM, 25 mM, 50 mM, 75 mM, 100 mM, and 200 mM NaCl solutions; and (5) 4,5,6,7,8,9 and 10 pH buffer solutions. All the treatments were applied on 100 seeds (five replicates, 20 seeds each) and incubated at 25° C under 12/12 hrs light/dark for 4 weeks. Final germination percentages were calculated. Seeds of Bidens pilosa, Mikania micrantha, Rivina humilis, Tridax procumbens, and Vernonia cinerea were identified as non-dormant (germination>90%) and seeds of Ageratum conyzoides, Hyptis capitata, Oldenlandia herbacea, Ocimum tenuiflorum and Spilanthes iabadicensis were identified as dormant (germination<65%). GA3 improved germination of S. iabadicensis and KAR1 improved germination of A. conyzoides, H. capitata, O. herbacea, and S. iabadicensis. Smoke water did not improve seed germination of any of the species. Seven species (B. pilosa, M. micrantha, O. herbacea, O. tenuiflorum, R. humilis, and T. procumbens) exhibited a wide range of salinity tolerance (0-75 mM NaCl) with>50% germination. R. humilis exhibited a wide range of pH tolerance (pH 5-8) with >50% germination. Seed dormancy of four species were broken by GA3 and KAR1 treatments indicating physiological seed dormancy (PD). Due to unresponsiveness to dormancy breaking treatments, it can be assumed that seed of O. tenuiflorum possess deep-PD. The study confirmed that responsiveness to KAR1, smoke, salinity and pH is species specific and seed dormancy may lead to the formation of persistent soil weed seed banks. These traits may facilitate the weed seeds to compete with other species and dominate the vegetation.Keywords: Karrikinolide (KAR1), pH, Smoke water, Salinity, Weed specie