Effect of rice straw extracts on growth of two phytoplankton isolated from a fish pond

Allelochemical use has been demonstrated as an eco-friendly method for control of algal growth. The present study was carried out to assess the effect of rice straw extract applications on the growth of the microalga Chlorella sp. and the cyanobacterium Anabaena sp. isolated from the Abbassa fish pond. Experiments were performed by preparing five treatments having different rice straw extract concentrations and a control without extract. Growth of Anabaena over 2 weeks was effectively inhibited by both water and methanol extracts and inhibition rates were dose-dependent. Inhibition was > 95% for the 1, 5, and 10 mg L-1 water extract treatments. In contrast, growth of Chlorella was stimulated by both extracts. Some phenolic-specific compounds responsible for allelopathic effect were identified using HPLC analysis. We conclude that the aqueous extract of rice straw is capable of significantly inhibiting the growth of Anabaena sp., providing a cheap and eco-friendly alternative for control of blooms of this cyanobacterium in fish ponds and other aquatic ecosystems. Additional assessment is required to determine the effects of these extracts for other cyanobacteria and microalgae.