External and Internal Root Colonization of Maize by Two Pseudomonas Strains: Enumeration by Enzyme-Linked Immunosorbent Assay (ELISA)

Maize root colonization by two fluorescent Pseudomonas strains M.3.1. and TR335, isolated respectively from maize and tomato roots, were studied in hydroponic conditions. Each bacterium was inoculated separately, and three different colonization areas were studied: nutrient solution, rhizoplane, and endorhizosphere. The two Pseudomonas strains established large rhizosphere populations, and rhizoplane colonization of the entire root system was similar for both strains. However, strain M.3.1. colonized the endorhizosphere more efficiently than strain TR335. Seminal root cuttings from the tip to the seed allowed the assessment of colonization of three different root areas (i.e., root cap and elongation area, root-hair zone, and mature zone). Rhizoplane colonizations of all these three areas by M.3.1. were significantly the same, whereas strain TR335 colonized the rhizoplane of the root cap and elongation area more actively than the root-hair zone and mature zone. Population size of the strain M.3.1. in the internal tissue of these areas was greater than that of strain TR335. Co-inoculations of the two strains indicated a stimulation of the population size of strain M.3.1. regardless of root area studied, whereas population size of strain TR335 remained unchanged. These results demonstrated that external and internal maize root tissues were colonized to a greater extent by a strain isolated from a maize rhizosphere than by one isolated from another rhizosphere. Received: 26 September 1996 / Accepted: 1 November 1996