Abstract: Four seasonal field investigations have been conducted in the Seven Stars Lake in Zhaoqing between Apr.1996 and Jan.1997. The water of the lake was sampled once for each season. Three major eutrophication elements, phytoplankton,nitrate and phosphate were analyzed quantitatively. According to the monitoring data,the concectration levels of the elements and their distributions,relationships among the elements were analyzed. The results are important for predicting eutrophication of the water and studying the mechanisms of the eutrophication in the Seven Sear Lake.

Key words: tobacco, biocontrol agents combination, growth and development, induced resistance, Phytophthora nicotianae.