PHOSPHOROUS MOVILIZATION IN STRAWBERRY PLANTS BY A STRAIN OF MESORHIZOBIUM MEDITERRANEUM WHICH NODULATES CICER ARIETINUM Alvaro Peix 1, Laura Martín-Martín 1, Eustoquio Martínez-Molina 1, Pedro F. Mateos 1, Claudino Rodríguez-Barrueco 2, Encarna Velázquez 1 Departamento de Microbiología y Genética. Universidad de Salamanca

 Phosphorous is, after nitrogen, the second most important element in plant nutrition  In many plants of agronomic interest, phosphorous is a key a key factor in fruit properties and precocity, which is very important under a commercial point of view  only 0.1% of the total phosphorous from soil is available to plants

 Among Plant Growth-Promoting Rhizobacteria, there are some strains which mode of action is based on solubilization of insoluble phosphates and mobilization of P in soil-plant interface  Among Phosphate Solubilizing Bacteria, the most powerful strains are included in diverse taxonomic groups, as Gram negative Proteobacteria (pseudomonads and rhizobia) and Gram positive bacteria of low G+C content (Bacillus).  Some strains of rhizobia and other related genera, besides their potential to nodulate legumes and fix atmospheric nitrogen, can solubilize phosphates and mobilize P to plants

The strain PECA21 is able to nodulate, fix nitrogen and movilize phosphorous to Cicer arietinum Phosphate solubilization halos of strain PECA21 grown in YED+ 0.3% tricalcium phosphate medium Identification Stable Low Molecular Weight (LMW) RNA profiles obtained by Staircase Electrophoresis

LMW RNA profiles LMW RNA profiles of type strains from Mesorhizobium nodulating Cicer arietinum and PECA21: Carril (1) M. ciceri USDA 3383 T Carril (2) M. mediterraneum USDA 3392 T Carril (3) PECA21

Phosphorous mobilization in strawberry plants TreatmentDry weight (g) P (%)N(%)Production (g/plant) Controls5.83a0.195a1.595a8.927a PECA215.46a0.242a1.625a3.714a PECA21-P5.50a0.309b1.670a18.046b values followed by the same letter are not significantly different from each other at p=0.05 according to Fisher's Protected LSD View of fruits yielded by plants from different treatments View of strawberry plants growing in growth chamber

Phosphorous mobilization in strawberry plants TreatmentDry weight(g) P (%)N(%)Production( g/plant) Control5.83a0.195a1.595a8.927a PECA215.46a0.242a1.625a3.714a PECA21-P5.50a0.309b1.670a18.046b values followed by the same letter are not significantly different from each other at p=0.05 according to Fisher's Protected LSD Bar charts of parameters measured in the experiment

 LMW RNA profiles obtained by Staircase electrophoresis allow the identification of phosphate solubilizing bacteria belonging to very diverse taxonomic groups. In our case strain PECA21 isolated from chickpea was identified as Mesorhizobium mediterraneum  In strawberry plants inoculated with strain Mesorhizobium mediterraneum PECA21 added with phosphate, phosphorous mobilization in plant-soil interface was observed, increasing significantly their P content.  Strawberry plants inoculated with strain Mesorhizobium mediterraneum PECA21 added with phosphate yielded fruit production higher than twice the quantity compared to control plants, and therefore this strains behaves as a good PGPR, showing potential as microbial inoculant for strawberry in the future. CONCLUSIONS