Fungal endophytes as promising antibacterial agents against ralstonia solanacearum, the cause of wilt disease in potato plants

All over the world, vegetable crops are suffering, including potatoes, which have been severely affected by bacterial wilt disease caused by Ralstonia solanacearum. Alternaria burnsii (A. burnsii), Aspergillus niger ( A. niger), and Aspergillus niveus ( A. niveus) are endophytic fungi that were isolated from Trifolium alexandrinum and were applied to enhance potato growth and stimulate defense mechanisms against Ralstonia solanacearum wilt (RSW) disease. The findings showed that the endophytic fungal filtrate possesses antibacterial activity against R. solanacearum in vitro, with inhibition zones for A. burnsii, A. niveus, and A. niger at concentrations of 1 mg/ml measuring 38.0 mm, 30.0 mm, and 28.0 mm in size. In pot trials, the mixture of A. burnsii, A. niveus, and A. niger was the most effective treatment. It reduced the disease index to 17.5% and provided 78.7% protection, followed using A. niger and A. niveus which reduced the disease index to 30% and 35%, respectively, and provided protection of 63.6% and 57.5%. Applying the fungal mixture to RSW-infected plants resulted in a 132.5% increase in soluble carbohydrates and a 94.3% increase in protein levels. The application of the endophytic fungi, singly or in combination, resulted in an increase in the phenolic content and the activities of antioxidant enzymes. Based on the study results, we recommend using a mixture of these tested endophytic fungi as therapeutic agents against RSW and as plant growth stimulants for commercial purposes.