Compatibility of biological control agents with fungicides against root rot diseases of wheat

Root - rot diseases are considered the most serious diseases of wheat in Egypt, causing a considerable loss seed germination, plant stand and grain yield. The present study aims to evaluate the fungicidal activity of four chemical fungicides and two biological control agents. Four fungicides (i.e. triticonazole, carbendazim, carboxin + thiram and metalaxyl M + fludioxonil) and two biological control agents (i.e. Trichoderma harzianum and Bacillus subtilis) were evaluated separately and their compatibility against two pathogenic fungi, Rhizoctonia solani and Fusarium graminearum that causing root rot diseases of wheat. The in vitro studies showed that the fungicidal activity of the tested fungicides against R. solani mycelial growth was descendingly arranged as follows; metalaxyl M + fludioxonil > carbendazim > triticonazole > carboxin + thiram, while it was metalaxyl M + fludioxonil > triticonazole > carbendazim > carboxin + thiram against F. graminearum mycelial growth. In greenhouse trials, the fungicides were applied at 1.5 and 3.0 g kg-1 seeds as seed treatment, while biological control agents were applied at 4.5 and 9.0 x 106 spores mL-1 water as soil treatment. The results showed that all the treatments significantly reduced disease incidence and increased emergence and plant stands and the biological control agents were the inferior treatments. Generally, the most effective treatments for controlling root rot diseases were metalaxyl M + fludioxonil followed by carbendazim, triticonazole, while the lowest were carboxin + thiram, B. subtilis and T. harzianum as compared with the control treatment. Moreover, the results concluded that the efficiency of T. harzianum and B. subtilis in controlling R. solani and F. graminearum was obviously enhanced by their compatibility with low rates of the tested fungicides. In conclusion, the biological strategy which used throughout integrated pest management could be improved by using fungicides at low rates.