Relationships of transgenic Bt cotton variety and soil nutrients with the severity of red leaf blight

The experiment was conducted in 2003 and 2004 to observe the effects of transgenic Bt cotton and soil nutrients on red leaf blight of cotton．The systemic investigations reveal that the severity of red leaf blight of transgenic Bt cotton variety is higher than that of non-Bt cotton variety, the disease incidence and index of transgenic Bt cotton variety are 47.95%～79.45% and 12.95～28.25, respectively and those of non-Bt cotton variety are 32.12%～55.06% and 9.09～15.75,respectively. Incidence reveals that a significant difference between Bt cotton and non-Bt cotton varieties(P<0.05). The ginned cotton yield and the severity of red leaf blight present no significant difference（P>0.05）among six treatments of N, P, K fertilizer combination. This result shows no significant effects of N, P, K fertilizer on reducing the severity of disease. On the basis of the results, a new theory and some new methods are discussed for the disease control.