Analysis of Pseudomonas community structure in soil and rhizosphere of agricultural plots under no-till management in Argentina

AGARAS, B; WALL LG; VALVERDE C

Medellín

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

In Argentina, 75% of agricultural soils are cultivated under no-till management. The public-private consortium BIOSPAS was created to evaluate the effects of this practice on the biology and productivity of soils. One of the focus groups is the pseudomonads, widely recognized as PGPR. We sampled soil and rhizosphere from plots under good agricultural practices (GAP) or bad agricultural practices (BAP), as defined by farmers. Neighboring grasslands with no cropping history served as reference. Samples were collected in February and September during the 2010 and 2011 campaigns. Viable pseudomonads were counted on Gould?s S1 selective plates and fluorescent colonies were enumerated under UV light. These 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. Soil plate counts showed a bias to lower bacterial load in BAP than in GAP plots. Rhizosphere values were on average two orders of magnitude superior to the corresponding bulk soil. The ratio between total pseudomonads (PT) and heterotrophic bacteria (HT) was higher in GAP than in BAP plots. Diversity indexes calculated from RFLP patterns of period 2010 were higher in summer samples (February) than in winter ones (September). oprF PCR-RFLP profiling showed a seasonal grouping, as MDS analysis of RFLP patterns separated summer from winter samples. This is a first approach to describe the dynamics of pseudomonads population in agricultural soils with extensive crops under no-till regime.