INTRODUCTION Now a days due to biotic and abiotic stresses leads to severe yield reduction. Biotic constraints includes like fungi, bacteria, virus, nematodes, weeds and insects which causes yield loss up to 31 to 42 per cent (Agrios, 2005). To manage these, farmers also using exhaustive amount of pesticide increases year by year. These results in environment pollution as well as negative effect on non target organisms. Continuous and tremendous uses of chemical pesticides create high selection pressure on pathogens and force them to undergo mutation and develop pesticide resistance races. One of the important biocontrol agent is Trichoderma, possessing reasonable biological control attributes belonging to species T. harzianum, T. ressey, T. asperellum, T. viridae, T. virens, T. aureoviridae, T. konigii etc. These fungi have been widely studied for their biocontrol activities viz., micoparasitism, antibiosis, competition for nutrient and space, niche exclusion, stress tolerance, induced resistance in plants as well as inactivation of the pathogen’s enzymes by producing various antimicrobial compounds. The most commonly used microbial biopesticides are living organisms, which are parasites for the pest of interest. These include biofungicides, bioherbicides, and bioinsecticides (Gupta and Dikshit 2010). Bio-control agents, manage pathogens either by producing many toxic metabolites specific to the pest, preventing establishment of other microorganisms through their modes of action. Application of certain compatible plant growth-promoting rhizobacteria (PGPR) with Trichoderma also increases phenlyalanine ammonia lyase (PAL) and peroxidase (PO) activities upto 50 and 25 per cent respectively (Sarma et al., 2015; Singh et al., 2015). PGPR’s are considered as one of the best strategies; a better alternative for sustainable agriculture, and a viable solution to meet the challenges of plant disease management, global food security and environmental stability. Use of PGPR’s due to its sustainable and environmentally friendly mechanisms of plant growth promotion, is becoming more widespread in the agricultural industry. PGPR’s helps in nutrient fixation, phosphorous solubalizaton, potassium solubaliztion, siderophore production, zinc solubilization and production of phytohormones. PGPR’s such as Bacillus, Pseudomonas, Arthrobacter, and Azospirillum are major genuses and have many species (Shah et al., 2021). In this study PGPR’s (Plant Growth Promoting Rhizobacteria) like Pseudomonas fluorescens, Bacillus megaterium, Azotobacter and Bacillus mucilagenosus were used. Besides the classic mycorrhizal fungi and PGPR’s, other plant-growth-promoting fungi such as Trichoderma spp. (Teleomorph: Hypocrea) can protected from numerous pathogens by responses that are similar to systemic acquired resistance (SAR) and rhizobacteria induced systemic resistance (Wees et al., 2015). So both PGPR’s and Trichoderma spp. frequently enhances root growth and development, crop productivity, uptake and use of nutrients and resistance to biotic and abiotic stress. Keeping in this view, investigation was undertaken to study the “Compatibility of Trichoderma spp. with plant growth promoting rhizobacteria”. MATERIALS AND METHODS Trichoderma spp. and PGPR’s. In this study, to check the compatibility between Trichoderma spp. and PGPR’s different Trichoderma spp. were used. Those are, Trichoderma asperillum, Trichoderma virens and Trichoderma aureoviridae and PGPR’s (Plant Growth Promoting Rhizobacteria) like Pseudomonas fluorescens, Bacillus megaterium, Azotobacter and Bacillus mucilagenosus. Compatibility test was carried out with the help of dual culture technique. Dual culture technique. Twenty ml of sterilized and cooled potato dextrose agar was poured into sterile Petri plates under aseptic condition and allowed to solidify. For evaluation of compatibility of Trichoderma with PGPR (Morton and Strouble 1955), the suspension of PGPR will be streaked one day earlier at one end of the of the Petri plate and the Trichoderma spp. of mycelial discs (5 mm) was placed at another end of the petriplate by leaving 2mm periphery of petriplate. In control only Trichoderma disc was placed. The plates were incubated at 27±1°C and zone of inhibition was recorded by measuring the clear zone between the margins of the organisms. The colony diameter in control plate was also recorded. The per cent inhibition of growth of the Trichoderma spp. with the PGPR’s was calculated by using the formula as suggested by Vincent (1947). I= (C-T)/C ×100 Where, I = Per cent inhibition C = Growth in control plate T = Growth in treatment plate RESULT AND DISCUSSION The study was aimed to identify the compatibility of Trichoderma spp. with different PGPR’s. In vitro study revealed that, among different PGPRs Bacillus mucilagenosus was found to be the best organism which showed compatibility with all the three Trichoderma species, Trichoderma asperillum, Trichoderma virens and Trichoderma aureoviridae i.e., with 100 per cent compatibility followed by Bacillus megaterium which exhibited the 100 per cent compatible with T. asperillum and T. aureoviridae whereas 98.45 per cent compatible with T. virens Whereas Azotobacter was 96.30 per cent compatibility with T. aureoviridae, followed by, Trichoderma asperillum and Trichoderma virens at 95.56 and 91.49 per cent, respectively. Also Pseudomonas fluorescens was found to be compatible with T. aureoviridae, T. asperillum and T. virens about 95.60, 75.93 and 80.38 per cent, respectively. All the three isolates of Trichoderma are showed about 80 to 100 percent compatability with Bacillus mucilagenosus followed by Bacillus megaterium, Pseudomonas fluorescens and Azotobacter. Due to different mode of action to inhibit the plant pathogens of Trichoderma and PGPRs. They are mutual in nature hence they are compatible with each other. Little bit inhibition due to siderophores and enzymes produced by PGPRs will hinder the growth of Trichoderma spp. They are equally antagonistic with each other individually (Table 1 and Fig. 1). The result was contradict with the results of (Lorito et al., 1993; Sridhar et al., 1993; Jayarajan and Ramabadran, 1999; Montealegre et al., 2003; Rudresh et al., 2005; Niranjan et al., 2009; Sandheep et al., 2013; Akthar and Tanweer 2014; Tanushree et al., 2017; Majumder et al., 2019) showed that PGPR’s and Trichoderma mixture were statistically at on par to manage plant diseases also increase in growth and development of the plants.