Beauveria bassiana Induces Strong Defense and Increases Resistance in Tomato to Bemisia tabaci

Pre-stimulation of plants can change their resistance mechanisms, thereby enhancing their defense responses. Beauveria bassiana, a broad-spectrum entomogenous fungi, can also induce plant defenses, but it received little attention. Here, we show that B. bassiana can act as a stimulus to prime tomato defense responses, improving resistance in the plant to herbivore stress. The results illustrated that four defense genes (PIN2, PR2, PAL, and MPK3) were upregulated in all B. bassiana treatments, especially the phenylalanine deaminase (PAL) gene, which was highly expressed in tomato plants after B. bassiana inoculation. Feeding through Bemisia tabaci resulted in a weak upregulation of defense genes. However, in combined fungal inoculation and B. tabaci feeding, a total of nine defense genes were upregulated, among which five genes—PAL, PPO, PIN2, PR2, and PR1—were closely related to the phenol synthesis. The results of tomato plant metabolism showed that B. bassiana mainly activates tomato phenylpropane metabolic pathways, with this modulation being influenced by jasmonate. Further explorations revealed a significant enhancement in the antioxidant capacity of the plants, as evidenced by the determination of their antioxidant compounds and the coloration of leaf phenolic substances. Thus, entomopathogenic fungi can act as an exogenous substance to activate the defense responses of tomatoes without damaging the plant, indicating a good potential for developing applications using B. bassiana to promote resistance in tomatoes for pest management.