Comparative Study on Effects of Chemical Fungicides and a Biocide on Cotton Seedling Damping-Off Caused by Rhizoctonia solani

Abstract

The present study evaluated the efficacy of the fungicides Moncut and Rizolex-T and the biocide Bio-Control T34 (Trichoderma asperellum) on suppressing incidence of cotton seedling damping-off caused by Rhizoctonia solani on cotton cultivar Giza 86. The dual treatments of the two fungicides and the biocide also evaluated in vitro and in vivo. In vitro studies showed that Moncut completely inhibited R. solani linear growth when it was applied at a rate of 250ppm, while Rizolex-T completely inhibited R. solani growth when it was applied at a rate of 125ppm. The biocide inhibited the linear growth of R. solani by 59.17%. The biocide growth was not affected by all the applied concentrations of Moncut, while it was partially inhibited by the high concentrations of Rizolex-T. Under greenhouse conditions, the two chemical fungicides suppressed incidence of damping–off, while the biocide was unable to suppress the disease. The use of Moncut before or after the biocide succeeded in reducing the disease incidence. On the other hand, Rizolex-T caused significant reduction in disease incidence only when it was applied before the biocide. The application half or fourth the initial dose of the chemical fungicides before or after the biocide caused significant reduction in the disease incidence. The application of Moncut by the initial dose followed by the biocide caused increases in the activity of polyphenol oxidase (PPO) and phenols and sugars contents of the seedlings. Application half the initial dose of Moncut before or after the biocide caused increases in the previously mentioned variables. The use fourth the initial dose of Moncut caused increases in the same variables when it was followed by the biocide, while the use of this dose after the biocide caused decreases in the same variables.