Comparative study of endophytic bacterial strains from non-host crops for enhancing plant growth and managing early blight in tomato

<i>Bacillus pseudomycoides</i>, <i>Paenibacillus polymyxa</i>, and <i>B. velezensis</i> are potent bacterial endophytes, which typically exhibit host-specific interactions. However, comparative studies of these endophytes <i>in vitro</i> and <i>in planta</i> in non-host crops are lacking. Therefore, in this study, we evaluated the potential of endophytes <i>B. pseudomycoides</i> strain HP3d, <i>P. polymyxa</i> strain PGSS1, <i>B. velezensis</i> strain A6, and P42, isolated from various crop ecosystems in promoting plant growth and inducing systemic resistance against early blight disease in tomato. <i>In vitro</i>, endophytes exhibited 44.44-55.56% and 37.50-87.50% inhibition of <i>Alternaria solani</i> in dual culture and volatilome bioassay, respectively. In the glasshouse, individual and combined applications via seed treatment (ST), seedling dip (SD), and foliar spray (FS) significantly enhanced shoot growth (23.63-57.61%), root growth (43.27-118.23%), number of leaves (77.52-93.58%), number of shoots (33.42-45.28%) and root dry matter (42.17-43.86%), reducing early blight (PDI) by 70.95-76.12% compared to uninoculated control. Enzymatic activities, including such as polyphenol oxidase (30-40 fold), peroxidase (65.00-75.00 fold), superoxide dismutase (34.20-37.20 fold) and phenylalanine ammonia-lyase (44.44-45.56 fold) were elevated post-inoculation in endophytes treated tomato plants challenged with <i>A. solani</i> compared to control treated only with <i>A. solani</i> and declined after the fifth day. The total chlorophyll content declined from the 0th to the 10th day, but endophyte treated plants exhibited lesser reductions (2.03-2.09) than uninoculated control. Field trials confirmed the glasshouse findings, showing reduced early blight and improved growth parameters in tomato where the ST + SD + FS combination emerged as the most effective treatment for all endophytes showing 1.06-1.88 fold increase in fruit yield per plant and 28.92-32.52% decrease in PDI compared to untreated control. Thus, the study highlights the broad-spectrum potential of these strains in promoting plant growth and controlling early blight in tomato, demonstrating non-host specificity. These endophytes offer eco-friendly alternatives to chemical pesticides, supporting sustainable agriculture. Their success in field trials suggests the potential for commercialization and large-scale use across diverse crops and pave the way for further interdisciplinary research to optimize their application in integrated pest management strategies.