Abstract
Bacterial wilt, caused by soilborne bacterium Ralstonia solanacearum, is one of the most severe diseases of tomato worldwide, and no successful control measures are available to date. In the present study, a sustainable alternative tool such as use of fungi from tomato rhizosphere is being utilized to combat the pathogen attack. The application of Trichoderma asperellum (T4 and T8) isolates delayed wilt development, effectively decreased the disease incidence, increased fruit yield, and improved plant growth promotion under field conditions. The T. asperellum treatment decreased the disease incidence by 51.06% (RS + T4) and 52.75% (RS + T8) in Bhoomishettihalli (BH) and 47.21% (RS + T4) and 46.83% (RS + T8) in Madanahalli (MH) plots, respectively when compared with the pathogen-treated plot in year 2014. Correspondent decreases in year 2015 were 50.69% (RS + T4) and 52.38% (RS + T8) in BH and 48.18% (RS + T4) and 49.22% (RS + T8) in MH plots. In year 2014, T. asperellum (T4 and T8) treatment enhanced the yield with 5.45 t/ha and 5.50 t/ha in BH plot and 6.66 t/ha and 6.93 t/ha in MH plot, respectively, when compared with infected plots. In year 2015, T. asperellum (T4 and T8) treatment enhanced the yield with 5.29 t/ha and 5.51 t/ha in BH plot and 5.82 t/ha and 5.66 t/ha in MH plot, respectively, when compared with infected plots. The disease control and yield enhancement were highest at T8, followed by T4. Increase in the level of peroxidase (POX), phenylalanine ammonium lyase (PAL), polyphenol oxidase (PPO), β-1,3-glucanase and total phenol activities at 12th, 10th, 14th, 12th, and 10th days, respectively, after pathogen inoculation was observed. This indicates the induction of plant resistance mechanism by T. asperellum against R. solanacearum in tomato plants under field conditions.
Highlights
Tomato (Lycopersicon esculentum) is one of the most widely cultivated vegetable crops worldwide
Field experiment for assessment of T. asperellum isolates to control of bacterial wilt The characterization of T. asperellum antagonism against R. solanacearum was the initial step in assessing the biocontrol capacity of these agents
Biochemical analysis The present results showed that the isolates of T. asperellum significantly induced maximum levels of defense enzyme activities in tomato leaves challenged with pathogen, compared with uninoculated tomato plants
Summary
Tomato (Lycopersicon esculentum) is one of the most widely cultivated vegetable crops worldwide. Vegetable crops are extremely prone to soilborne and root diseases causing huge losses in yield and its quality (Sharma et al 2004). The main constraint to tomato production in many parts of the world is several plant diseases. Bacterial wilt is a destructive and prevalent soilborne disease that limits tomato production in the tropics, subtropics, and warm temperate regions of the world (Ramesh et al 2014). Ralstonia solanacearum is one of the most severe quarantine important diseases of tomato worldwide. Its host range contains solanaceous species, leguminous species, a small number of monocotyledons, trees, shrubs, and certain ecotypes of the model plant Arabidopsis thaliana. The pathogen persists in soils, water, or reservoir plants for several years to form latent infections within native weeds contributing to the hard eradication of the bacterium (Avinash et al 2016)
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