Effect of light quality and intensity on emergence, growth and reproduction in Chromolaena odorata.
Chromolaena odorata is a perennial weed which invades forest areas cleared for developing plantations, nurseries, young plantations, and wastelands, but is conspicuously absent in the interior of dense forests or established plantations with closed canopy. The fresh seeds of C. odorata were found to be photoblastic; however, storage and washing substituted for light. 150 lux was sufficient to promote seed germination to a maximum of 68%. Higher intensities were less effective and those higher than 1500 lux were inhibitory. White and red light were promontory, while blue, far red and green were inhibitory. Light passing through leaf canopy was more inhibitory than far red light. Emergence of chromolaena was favored by low light intensity but for optimal seedling growth, higher intensities of 3000 to 3500 lux were found essential. Besides the light intensity, the quality of light had a very specific effect on the plant growth of C. odorata. Red and white light favored growth while blue, green and far red inhibited. Besides this, only those plants exposed to red and white light completed their life cycle by producing flowers. This study reflects on the strong light requirement of chromolaena for germination, seedling growth and seed production.