Trichoderma viridis and Bacillus bellesiae cooperate to control tomato bacterial wilt

Tomato bacterial wilt is a soil-borne disease caused by solanocrella, which seriously harms the tomato industry. Bacterial wilt is a systemic disease that causes root necrosis and vascular bundle Browning, which can inhibit nutrient absorption and lead to plant death. At present, the control of tomato bacterial wilt in the field is mainly based on chemical pesticides, but sometimes the effect is not significant, and it is easy to cause soil pollution. Biological control of plant diseases is an ecological and environmental protection method to ensure the sustainable development of agriculture. Bacillus and Trichoderma have been successfully used to control a variety of plant bacterial and fungal diseases. Their biocontrol mechanisms include producing antagonistic substances, parasitism/hyperparasitism, competing with pathogenic bacteria for nutrients and space, and inducing plant resistance. Many studies have shown that the combined use of two or more biological control agents is more effective than the use of a single biological control agent for disease control.

By treating tomato plants individually and in combination with Trichoderma virens Tvien6 and Bacillus velezensis X5, The incidence rate, plant height, plant weight, activity of PPO, POD and SOD, SPAD value and metabolite content of tomato bacterial wilt were determined to understand the synergic control effect of Tvien6 and X5 on tomato bacterial wilt.

It was found that the co-culture filtrate of Tvien6 and X5 significantly reduced the growth of Ralstonia solanacearum RS-15 compared with that of Tvien6 or X5 alone. The pot pot results showed that Tvien6 and X5 could increase plant height, plant weight and SPAD value of tomato, and significantly reduce the incidence of tomato bacterial wilt, and the combined use of the two strains was more obvious. The results showed that in most cases, the PPO, POD and SOD activities of the four treatment groups were in the order of TBR group (Tvien6+ X5 + RS-15) > BR group (X5 + RS-15) and TR group (Tvien6+ RS-15) > R group (RS-15). The results showed that Tvien6 and X5 could increase the activities of PPO, POD and SOD. However, the combination of Tvien6 and X5 has a stronger induction effect on the activity of defense enzymes, indicating that TVIEN6 and X5 have a synergistic effect on the induction of defense enzyme activity. Analysis of their metabolic changes by GC-MS showed that in 4 treatments, only 16 metabolites were obtained by GC-MS, 13 of which were clearly identified. Principal component analysis showed that there were significant differences in metabolite profiles between the biocontrol agent treatment group and the pathogen treatment group, while the differences between the BR and TR treatment groups were not obvious. The results showed that the contents of D-fructose and D-glucose in tomato were increased after Tvien6 and X5 treatment. When the two biocontrol microorganisms were combined, D-fructose and D-glucose increased significantly, indicating that Tvien6 and X5 synergically promoted the accumulation of D-fructose and D-glucose in tomato.

Enzymes such as PPO, POD, SOD and substances such as fructose and glucose can significantly improve plant disease resistance. As the carrier of photosynthesis, chlorophyll content was positively correlated with plant growth. In addition, fructose and glucose are also closely related to plant growth. In this study, the treatment of a single strain significantly improved the growth performance and disease resistance of tomato plants compared with the control. Compared with Tvien6 or X5 alone, the combined treatment of Tvien6 and X5 was more effective in inhibiting the growth of solanacra, promoting the growth of tomato plants, increasing the relative chlorophyll content of leaves, enhancing the activity of defense enzymes and increasing the accumulation of nutrients. In summary, the combination of Tvien6 and X5 has a synergistic effect, which is an effective way to prevent and control tomato bacterial wilt. The results of this study also further demonstrate that using a variety of different types of beneficial microorganisms is an efficient way to improve crop growth and increase disease resistance.

FIG. 1. Effects of Trichoderma viridis (Tvien6) and Bacillus Velez (X5) on Solanorella and tomato plants

FIG. 2 Effects of Trichoderma viridis and Bacillus Velez-induced PPO, POD and SOD activities in tomato plants