CONICET | Buscador de Institutos y Recursos Humanos

Lycopersicon esculentum colonization and plant growth promotion effects by inoculation with Gluconacetobacter diazotrophicus 1 María F. Luna, 2 Juan M. Crespo, 3 María L. Galar, 4 Néstor Mezquiriz and 5 José L. Boiardi 1Research scientist-CIC-PBA; 2Graduate studentUNQUI; 3Professional-CONICET; 4Professional-EEG-PBA; 5Research scientist-CONICET. CINDEFI (UNLP; CCT-La Plata, CONICET) La Plata. Argentina. A N2-fixing endophytic bacterium, Gluconacetobacter diazotrophicus, was described by Cavalcante and Döbereiner as associated with sugarcane1. This bacterium has also been found in natural association with other host plants. It can enhance plant growth independent of nitrogen fixation as has been shown in sugarcane and maize2. The potentially plant growth stimulation by this bacterium can be a consequence of production of phytohormones, biocontrol of phytopathogens and mineral nutrient solubilization. Its colonization behavior has been poorly characterized in plants others than sugar cane and the understanding of the bacterial colonization patterns is a critical prerequisite for the development of effective inoculants. Aiming to find potentials Plant Growth Promoting Bacteria (PGPB) for horticultural species, two sets of experiments were performed in tomato plants (Lycopersicon esculetum, cv. superman): i) inoculating seedlings (4 days postgermination) to study the colonization pattern of G. diazotrophicus Pal 5 and UAP 5541/pRGS561 (containing the marker gene gusA) under gnotobiotic conditions, and ii) inoculating seedlings (20 days postgermination) to evaluate plant growth promotion effects of G. diazotrophicus Pal 5 under production conditions. Colonization patterns were monitored by dilution plating assays and microscopic localization after staining with gus substrate. Root endophytic population densities were higher than 5 log CFU/g fresh weight. Aerial tissues were also colonized (~4-5 log CFU/g fresh weight). Microscopic localization showed bacteria colonizing root-stem junctions, sites of emergence of lateral roots, root hairs, stem sub-stomatal cavities and external cell layer on root transversal sections. The plant growth promoting activity was determined by measuring total tomato production during 4 months in two independent experiments. Results showed that seedling inoculation of tomato with G. diazotrophicus PAL 5 increased both number and weight by 6-7 % and 11-13 %, respectively, as compared to uninoculated controls. These results show that seedling inoculation with G. diazotrophicus led to extensive root colonization of tomato followed by bacterial spreading to aerial tissues. This colonization was accompanied by a significant increase of tomatoes production. 1. Cavalcante and Döbereiner (1988), Plant Soil 108:23-31 2. Riggs et al. (2001), Austr J Plant Physiol 28:829-836 2. Saravanan et al. (2008), Microb Ecol 55:130140