Bacillus subtilis- and Pseudomonas fluorescens-Mediated Systemic Resistance in Tomato Against Sclerotium rolfsii and Study of Physio-Chemical Alterations

Abstract

The present study is a comparative study between Reactive Oxygen Species (ROS) signaling and antioxidative enzymatic signaling and deals with induced systemic resistance (ISR) in enhancing the disease resistance in typical tomato plant (Solanum lycopersicum L.) infected by the collar rot fungus, Sclerotium rolfsii (Teleomorph: Athelia rolfsii) by priming with Bacillus subtilis, Pseudomonas fluorescens, and their microbial consortia by a single strain of Bacillus subtilis, and P. fluorescens as well as by developed microbial consortium with both bacteria. Leaf samples were collected after different durations of pathogen inoculation, i.e., 1, 2, 3, and 4 days, and the systemic level of oxidative stress parameters, such as hydrogen peroxide (H2O2), photosynthetic apparatus, superoxide radicals, and enzymatic antioxidants, were studied. Plant mortality under various treatments in two different seasons was calculated. The highest H2O2 was scavenged by the microbial consortium-treated plants (B1P1) and the lowest in pathogen-challenged plants (PC) compared to the untreated control. Cellular damage and reduction in the chlorophyll pigments were the highest at 48 h, and the photosynthetic efficiency (Fv/Fm) was evaluated from 24 to 96 h; the lowest values were observed for pathogen-challenged plants and the highest for B1P1. Enzymatic antioxidants showed the maximum value for B1P1 and the minimum for PC compared to the unchallenged control. Furthermore, an analysis of variance and principal component analysis (PCA) were conducted to examine the effect of the evaluation time (ET) and inoculation conditions (ICs) alone and in combination (ET × IC) on the physiological and biochemical parameters; accordingly, the score and the loading plots were constructed. Tomato root sections inoculated with different treatments were observed through scanning electron microscopy (SEM) to validate the potentiality of primed biocontrol agents in controlling the invasion of the pathogen. Further studies on the potential of this isolate to enhance the plant growth at the field level would strengthen the possibility of using the isolate as an alternative for organic fertilizers and pesticides.