Introduction
Controlling damages caused by pests and pathogens, especially soil-borne diseases related to tomato plants, has a significant role in improving the quantitative and qualitative performance of its production (Chen and Roberts, 2003; FAO, 2020). Fusarium wilt of tomato is known as one of the important diseases of this plant in fields and greenhouse conditions (Abdel-Monaim, 2012; Cha et al., 2019). Also, root-knot nematodes (including species of the genus Meloidogyne) are the most important plant parasitic nematodes from an economic point of view in the world. Biological control is one of the natural methods of controlling plant pathogens and reducing their damage to plants (Migunova and Sasanelli, 2021). Many bacteria and fungi are used to control pathogens in different plant species, which have different antagonistic potential against different pathogens (Siddiqui and Akhtar, 2008; Bai et al., 2018). Some biological products, such as vermicompost, are also used as alternative or complementary methods in the biocontrol of pathogens (Yatoo et al., 2021). these products can significantly reduce the pathogenicity levels of soil pathogens (Basco et al., 2017; Bisen and Singh, 2019).
The effect of biocontrol agents and fertilizer products, such as vermicompost, in improving the resistance of tomato plants to soil pathogens has been separately investigated in various studies. However, only some studies have evaluated the effects of the combined use of these agents. The present study was conducted to investigate the effect of the combined use of biological inhibitors and vermicompost on the control of soil pathogens.
Controlling damages caused by pests and pathogens, especially soil-borne diseases related to tomato plants, has a significant role in improving the quantitative and qualitative performance of its production (Chen and Roberts, 2003; FAO, 2020). Fusarium wilt of tomato is known as one of the important diseases of this plant in fields and greenhouse conditions (Abdel-Monaim, 2012; Cha et al., 2019). Also, root-knot nematodes (including species of the genus Meloidogyne) are the most important plant parasitic nematodes from an economic point of view in the world. Biological control is one of the natural methods of controlling plant pathogens and reducing their damage to plants (Migunova and Sasanelli, 2021). Many bacteria and fungi are used to control pathogens in different plant species, which have different antagonistic potential against different pathogens (Siddiqui and Akhtar, 2008; Bai et al., 2018). Some biological products, such as vermicompost, are also used as alternative or complementary methods in the biocontrol of pathogens (Yatoo et al., 2021). these products can significantly reduce the pathogenicity levels of soil pathogens (Basco et al., 2017; Bisen and Singh, 2019).
The effect of biocontrol agents and fertilizer products, such as vermicompost, in improving the resistance of tomato plants to soil pathogens has been separately investigated in various studies. However, only some studies have evaluated the effects of the combined use of these agents. The present study was conducted to investigate the effect of the combined use of biological inhibitors and vermicompost on the control of soil pathogens.
Materials and methods
The present study was conducted to investigate the effect of using vermicompost enriched with bacteria and fungi on growth parameters of tomato plants infected with root-knot nematode (Meloidogyne javanica) and Fusarium wilt (Fusarium oxysporum). Vermicompost applications were considered at control, optimum, and excessive levels. Biocontrol agents were mycorrhizal fungi (Glomus mosseae) (G.) and two antagonist bacteria (Bacillus subtilis (B.) and Pseudomonas putida (P.)). These biocontrol agents were used individually (B.; P.; G.), in binary combinations (B. & P.; B. & G.; P. & G.), and also in a ternary combination (B.P.G.) at different levels of vermicompost application. Growth parameters, including shoot wet and dry weights, root wet and dry weights, and chlorophyll index, were measured at the end of the experiments.
Results and discussion
The lowest values of wet and dry weights of aerial parts under the triple effects (P < 0.001) of vermicompost level, enrichment treatments, and pathogens belonged to the control condition, and the highest levels of these parameters were obtained with B. & G., and B.P.G treatments under application of vermicompost excessive level and with F. oxysporum. In each enrichment treatment, the values of these parameters were higher in enrichment with G. mosseae than B. subtilis, and P. putidae was at the next level. The optimum and excessive vermicompost treatments showed higher amounts of wet and dry weights of aerial parts compared to the control condition (no use of vermicompost).
The lowest values of wet and dry weights of aerial parts under the triple effects (P < 0.001) of vermicompost level, enrichment treatments, and pathogens belonged to the control condition, and the highest levels of these parameters were obtained with B. & G., and B.P.G treatments under application of vermicompost excessive level and with F. oxysporum. In each enrichment treatment, the values of these parameters were higher in enrichment with G. mosseae than B. subtilis, and P. putidae was at the next level. The optimum and excessive vermicompost treatments showed higher amounts of wet and dry weights of aerial parts compared to the control condition (no use of vermicompost).
The results of root wet and dry weight indicated that treatments with no use of vermicompost and without enrichment led to the lowest levels of these parameters for both pathogens. Vermicompost application at optimum and excessive levels resulted in higher wet and dry weights, especially for the treatments with G. mosseae enrichment (including G. mosseae, B. & G., P. & G., and B.P.G). The highest levels of these variables were obtained with the excessive vermicompost level and under the effect of F. oxysporum.
The lowest chlorophyll index score was obtained under the effect of both pathogens and its highest levels belonged to the F. oxysporum. Comparing the means for the interaction of vermicompost and enrichment indicated the highest chlorophyll index in B.P.G. enrichment treatment and the lowest index level was measured with the control condition (i.e., no use of vermicompost).
Conclusion
The findings of the present study showed that using biocontrol agents combined with vermicompost application can significantly improve the resistance of tomato plants against soil-borne diseases and lead to higher levels of root and aerial parts growth and better photosynthetic performance. This effect was much higher using the simultaneous application of all biocontrol treatments compared to their separate usage.