Abstract

The population density of Fusarium oxysporum f. sp. vasinfectum, disease index of cotton fusarium wilt along with the relation of the wilt disease and pathogen density in long-term cotton plantations were studied by the methods of dilution plating and field investigation. Microsclerotium densities of Verticillium dahliae and disease index of verticillium wilt were also studied. The results showed that both pathogen densities were first increased and reached their maximum at the 10^th continuous cropping year and then, gradually decreased. Very similarly, the disease indexes of fusarium and verticillium wilts exhibited the same variation trend, thereby, indicating that disease-suppressive soil may be formed in long-term cotton plantations that need to be further studied.

Key words: Long-term cotton plantations, continuous cropping, fusarium and verticillium wilt diseases, Fusarium oxysporum f. sp. vasinfectum, Verticillium dahliae, microsclerotia, population density, disease-suppressive soil.