Abstract

The phenotype of a plant is strongly influenced by the presence of neighbouring plants often resulting into change in growth and development. We have demonstrated to our knowledge for the first time, the influence of three aquatic weed species (Commelina sp., Justicia sp. and Vossia cupsidata) on growth and development of water hyacinth (Eichhornia crassipes). We found that Commelina sp., Justicia sp. and V. cupsidata significantly (P < 0.001) suppressed water hyacinth total fresh weight when growing together both in the Kagera River and greenhouse. Justicia sp. gave the highest (51%) water hyacinth fresh weight reduction when compared to fresh weight in pure stand probably due to competition effect. In the Kagera River but not greenhouse, water hyacinth plants were significantly taller (F _(4,1371) = 150.53, P < 0.001) in pure stands than when growing in mixtures. V. cupsidata strongly suppressed water hyacinth plant height although water hyacinth compensated by producing elevated number of ramets (daughter plants). In greenhouse environment, the number of ramets per plant was higher in mixtures than in pure water hyacinth treatment. Correlation analysis revealed a strong significant negative relationship between plant height and number of ramets. Competition for space and resources was suggested to be the major influential factor as water hyacinth in pure stands tended to have higher density and total biomass per unit area than when grown in mixtures. Analysis of water hyacinth ratios to other aquatic weeds showed a significant effect on water hyacinth growth and development in terms of fresh weight, plant height, leaves per plant and ramets. These data show that neighbouring aquatic weeds are important component in the regulation of water hyacinth growth and development in the aquatic ecosystem. 

Key words: Commelina sp., Justicia sp., Kagera River, water hyacinth.