Evaluation of Trichoderma and Bacillus Species for the Management of Watermelon Charcoal Rot and Plant Growth Promotion

Macrophomina phaseolina responsible for watermelon charcoal rot, is a soilborne pathogen spread worldwide and in Tunisia. This study aimed to control this important disease using eco-friendly treatments. Two fungal and one bacterial antagonists were tested. Dual culture trials showed the efficacy of Trichoderma harzianum, Trichoderma viride and Bacillus subtilis to reduce M. phaseolina mycelial growth by 36.45% to 53.67% for MP4 and MP1 isolates confronted to B. subtilis. In the in vivo tests, the use of T. harzianum and B. subtilis and their combination showed that the preventive application is more effective than the simultaneous and the curative treatments. In fact, the preventive application of T. harzianum and B. subtilis and their combination reduced the disease severity index by 37.5%, 91.75%and 25%, respectively, compared to the inoculated control. Preventive application of B. subtilis significantly enhanced root volume, root length, and shoot length by 81.81%, 67.41%, and 73.07%, respectively, compared to the inoculated control. The application of B. subtilis, T. harzianum and their combination simultaneously with inoculation significantly increased the length of plants by 99%, 90.85% and 34.11%, respectively, compared to the inoculated control. Our findings indicate that T. harzianum and B. subtilis can be effectively employed as preventive soil treatments to suppress charcoal rot and promote watermelon growth.