Rhizosphere selection of specific pseudomonads from soil

MARRERO M; AGARAS, B; WALL LG; VALVERDE C

Quirama, Nedellín

Workshop; 9th International and 1st Latinamerican PGPR Workshop; 2012

International PGPR Group

In contrast to rhizobial-legume symbiotic associations, the degree of specificity displayed by pseudomonads colonizing the rhizosphere seems to be comparatively less strict. However, diversity studies point to a relevant influence of plant species on the selection of specific pseudomonads among resident soil population. In order to address the influence of extensive crops on shaping the structure of soil pseudomonads, we carried out a trapping experiment using surface-disinfected seeds of different crop species cultivated in Argentina. Wheat, soybean or maize seeds were planted in a typical Argiudol soil with no agricultural management history. After 20 days in a greenhouse, roots were harvested, weighed and shaken vigorously in saline solution before plating onto pseudomonads selective medium S1. Plates bearing the most abundant pseudomonads from each sample, served as DNA source to carry out community structure analysis of oprF and gacA genes, formerly reported as Pseudomonas genus markers, by means of PCR-RFLP using newly designed primers. Fingerprints were analyzed using Gelcompar II v.4.602. The pseudomonads load of bulk soil was 6.280.15 log10 CFU/g (dry weight), whereas the rhizospheric load was 4.03±0.29 log10, 4.55±0.26 log10 and 4.12±0.13 log10 CFU/g (fresh weight), for maize, wheat, and soybean, respectively?.