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 species