Invetingation of Rhizosphere Soil Associated Protist Interaction with Plant Growth Promoting Bacteria and Their Effect on Rice Oryza Sativa L Plant Growth

Abstract

Agricultural sustainability is possible only when dependency on chemical fertilizers can be reduced to enhance crop yield to feed rapidly growing populations. Though traditional single bioinoculants play a crucial role in improving crop yield; they still find challenges in the fields due to low reproducibility in different soil types, crop cultivars, agro-ecological conditions and multiple biotic and abiotic stresses. A little information is available regarding their interactions with other microbes, survival, and efficiency in the soil. This includes multiple biotic interactions that either constrain or enhance their fitness in the soil. The presence of protists in the rhizospheric region of plants has been suggested as one of the possible reasons for the increased activity and survival of PGPB in the soil. Therefore, the present study was undertaken to investigate the protist-PGPB interactions at the laboratory scale as well as under greenhouse conditions and to develop targeted applications of PGPB with protists. Six different genera of soil protists including Acanthamoeba, Vermaamoeba, Colpoda, Tetrahymena, Crytolophosis, and an unidentified genus of the family Kreyellidae were identified to be associated with rice rhizosphere soils. Predatory action of different genera of protists on three different PGPB species such as E. cloacae, B. cereus and P. fluorescens revealed diverse grazing effects of protistan isolates on selected PGPB. The PGP properties of the bacterial strains significantly changed in response to protest predation under in vitro laboratory conditions, suggesting that protists may be an newlineimportant driver of plant beneficial bacteria and their activity. Together, protists and PGPB significantly enhance plant growth through various mechanisms. These include altering the root structure and auxin responsive GH3-2 gene expression in rice roots, increasing the uptake of N and P by plants, and influencing soil respiration enzyme activities, siderophore and EPS and available N and P content.