Seed Germination and Seedling Growth of Tithonia diversifolia (Hemsl.) A. Gray, the Mexican Sunflower
*Agboola D.A., W.F. Idowu and M. Kadiri
Department of Biological Sciences, University of Agriculture, P.M.B. 2240, Abeokuta, Ogun State, Nigeria. *Corresponding author. + 234 (0) 803 4073 824 email: jareagbo@yahoo.com
Accepted in January 2004.
ABSTRACT
Studies on the seed germination and seedling growth of Tithonia diversifolia (Hemsl.) A. Gray, the Mexican sunflower, was carried out. This involved the usage of some dormancy-releasing methods and the effect of some concentrations of three herbicide formulations on the young seedlings. Initial germination tests on fresh and stored seeds revealed a low percentage germination of less than 30%. The seeds of the weed exhibit dormancy. Subjecting the seeds to wet heat at 80 oC and 100oC and light treatment terminated dormancy both in the fresh and stored seeds. Light greatly enhanced the germination percentage of hot water – treated fresh seeds by about 70%. There was gradual increase in germination percentage with increase in storage period in dormancy-released seeds. The mean LAR (Leaf Area Ratio), NAR (Net Assimilation Rate) and RGR (Relative Growth Rate) are comparatively high in young seedlings. Concentrations of 0.5 – 2.0% of Gramoxone, Primextra and Galex are toxic to 1-month-old seedlings. The physiological basis of dormancy in the seeds of this noxious weed species as revealed through after-ripening and light requirements by the embryo are discussed.