Factors affecting germination of Siam weed (Chromolaena odorata (L.) King & Robinson) seeds
B.S. Ismail, B.I. Rosmini and K. Samiah, Department of Botany, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysia.
Effects of several environmental factors on germination and emergence of Siam weed(Chromolaena odorata (L.) King & Robinson) were examined in laboratory and greenhouse. Total germination was reduced in dark conditions (25%) compared to that in alternating light/dark conditions (90%). The highest level of germination was observed when seeds were exposed to alternating light/dark together with the application of gibberellic acid (GA3). The optimum alternating temperature 20/30°C resulted in 84% germination at day 10. Germination was reduced under simulated moisture stress, and no germination was observed at -1.19 MPa. Maximum germination (87%) occurred at pH 7. Increasing NaCl concentration reduced the germination percentage (12% recorded at 170 mM) and growth of Siam weed. Greater emergence was obtained when seeds were sown on the soil surface (73% in Serdang Series and 88% in Sungai Buluh Series), but no seedlings emerged when seeds were planted 2 cm deep. Shade levels of 50 and 70% reduced plant dry matter by 50 and 63% respectively relative to growth in full sunlight. The number of leaves and leaf area also decreased significantly in plants grown under 50% shade as compared to those receiving full sunlight.
Plant Protection Quarterly (1996) 11 (1) 2-5.