Effects of plant growth-promoting rhizobacteria combined with composts obtained from rose oil processing wastes on organic tomato seedling production

The objective of this experiment was to assess the performance of compost in organic growing medium with plant growth-promoting rhizobacteria (PGPR) for organic tomato cultivar 'Rio Grande' seedling production. The study was conducted during the spring growing season of 2017. Two different composts previously obtained from a mixture containing rose oil processing wastes, separated dairy manure, poultry manure, and straw composted by two methods (aerated static pile: ASP and turned windrow: TW) and their mixtures (1:1 and 1:3; v/v) with local peat (LP) were used as a growing medium. Seeds treated with Bacillus subtilis and Pseudomonas fluorescens were sown on March 7, 2017. Peat and non-PGPR treated seeds were used as controls. All media were sifted before use. After 3 days in germination room, seedlings were moved to a PE greenhouse specialized for seedling growing. Liquid organic fertilizer was used for fertilization. Some physical and chemical properties of each growing medium, seed germination rate and period of seeds, seedling vigour, leaf color and SPAD index for chlorophyll were determined. The effects of PGPR on most measured parameters were found significant. Among the tested PGPRs, B. subtilis improved seed germination rate and vigour, reduced germination period and leaf chlorophyll content. Based on the seed vigour test, peat and compost produced from ASP showed better performance and were found comparable. In conclusion, compost produced from ASP can be used in organic tomato seedling production and B. subtilis × 50% compost-ASP + 50% LP was found to be the most promising based on the measurements of seedling growth parameters. © 2020 International Society for Horticultural Science. All rights reserved.