Location of bacteria on the surface and in the interior of root and stem of brinjal (Solanum melongena L.) plants

Rhizosphere, phylloplane and caulosphere is the region where a complex community of microbes, mainly bacteria and fungi are present. The microbe plant interaction in these regions can be beneficial, neutral, variable, or deleterious for plant growth. The objective of the study was to locate the bacteria present on the surface and in the interior of root and stem of brinjal (Solanum melongena L.). The seeds of 16 cultivars of brinjal (Solanum melongena L.) viz., Arka keshav, Arka shirish, Arka kusumaker, and IIHR accession numbers 389,386,387,377 Tc, BB44, 391, 433, 434, 427, 447, 448, 476 and 487 that were used in the initial screening experiment were obtained from the Department of Vegetable crops, IIHR, Hessaraghatta, Bangalore. Brinjal (Solanum melongena L.) Plants of different varieties were collected from seven locations around Bangalore viz., Hessaraghatta, Yelahanka, Kengeri, Madi vala, Hebbal, Tirumalapura and Attibele were also screened for the presence of associative bacteria. The location of bacteria on the surface and in the interior of root and stem of brinjal were observed under light microscope, transmission electron microscope and scanning electron microscope. The bacteria were present on the root cap, root hairs, root tips and region of cell elongation when viewed under light microscope. Light microscopic observations of root and stem sections revealed the presence of bacteria at various depths in the cortex between the epidermis and endodermis occupying the intercellular regions. Bacteria were also observed inside the cortical cells and in the cells of the vascular region. The number of bacteria present in the root region was significantly higher than in the stem. In stem, the bacteria were predominant on the epidermal layer and cortical tissue as observed under transmission electron microscope. Under scanning electron microscope, the bacteria were present as aggregates, each aggregate containing several cells. Fibrillar anchoring of the bacteria to the root hair were observed and the bacteria were present even at the base and on the stem and leaf hair. For the first time the presence of growth promoting bacteria on the rhizosphere and endorhizosphere of brinjal (Solanum melongena L.) cultivars was established. The bacteria were localized on the root cap, root hairs, root tips, region of cell elongation, at various depths in the cortex between the epidermis and endodermis occupying the intercellular regions. Bacteria were also present inside the cortical cells, in the vascular region, epidermal layer, cortical tissue, at the base and on the stem and leaf hair.