|Institution:||University of Florida|
|Keywords:||abscisic, bahiagrass, cogongrass, competition, dormancy, light; Agronomy|
|Full text PDF:||http://ufdc.ufl.edu/UFE0024081|
Cogongrass [Imperata cylindrica (L.) Beauv.] has been reported as a serious perennial pest throughout the tropical and subtropical areas of the world and has been ranked the 7th worst weed worldwide. It is an invasive C4 grass weed, and possesses a very strong and aggressive rhizome system, which is the major reason for its survivability and competitiveness. The low shoot to rhizome ratio greatly contributes to energy conservation and rapid re-growth after chemical and mechanical control methods such as burning or cutting. Cogongrass thrives better in soils with low pH (pH about 4.7), low fertility, low organic matter, although it can grow in a wide range of soils. The goal of this research is to provide biological information concerning cogongrass growth and competitiveness to facilitate future research on integrated management of cogongrass. The first experiment evaluated the influence of soil pH on the relative competitiveness of cogongrass and bahiagrass. Based on previous research on different pH requirements for optimal growth of cogongrass and bahiagrass (cogongrass about 4.7, bahiagrass about 5.5 to 6.5), we hypothesized soil pH would influence the competition between these 2 species. Our results showed that when soil pH increased, bahiagrass competitiveness was increased and cogongrass competitiveness was decreased. Therefore, cogongrass invasion into bahiagrass pastures appears to be strongly related to soil pH. The second experiment evaluated light intensity effects on cogongrass growth. Mature and young cogongrass plants were grown under different light intensity levels (75, 25, 15, 2, and 1% of full sunlight) to measure growth patterns and changes in rhizome to shoot ratio. Mature plants had a completely developed rhizome system, and under low light intensities, the plants maintained a constant rhizome to shoot ratio. At light intensity below the light compensation point, rhizome to shoot ratio increased dramatically indicating possible rhizome dormancy. Young plants sacrificed rhizome growth for shoot production with rhizome to shoot ratio decreasing as light intensity decreased. The third experiment evaluated abscisic acid (ABA) concentration in cogongrass rhizomes and rhizome scale leaves as a function of apical position. The relationship between ABA concentration and rhizome dormancy was evaluated. Our results showed that ABA likely plays a role in cogongrass rhizome dormancy. The rhizome position that includes rhizome tips, the ABA concentration was significantly higher than in axillary nodes, including shoots and scale leaf tissue. Further research is still needed to confirm the actual function of ABA in cogongrass rhizome dormancy and the complex interaction between different plant growth hormones, such as auxin, also needs to be addressed in the future.