Used mainly for sucrose production, sugar beet is one of the most important crops in Castilla y León (Spain). Several studies have demonstrated the benefits of microorganisms in different crop management programs, among which Plant Growth Promoting Rhizobacteria (PGPR). This research aims to assess the beneficial effects of two PGPRs strains (Pseudomonas fluorescens Pf0-1 and Pseudomonas chlororaphis CECT 462) on sugar beet (Beta vulgaris) production. Three treatments: a PGPRs co-inoculation assay of untreated seeds without any chemical treatment (TB), a conventional treatment with commercial seeds and fungicide application (TT); and a control with seeds without protective coating, bacterial inoculation and chemical treatment (ST). The efficacy of PGPRs inoculation on sugar beet production was determined measuring periodically the photosynthetic status of plants, and the final yield and quality of tubers. Aerial and root plant biomass, maximum beet perimeter, polarization, and sugar values of the sugar beet plants inoculated with PGPRs showed higher values and significant differences to sugar beet subjected to other treatments. We could see that PGPRs inoculation (TB treatment) produced significant differences in the quantum yield of PSII (ΦPSII). TB showed the highest value for ΦPSII and the NPQ (non-photochemical quenching), the lowest value, even though the PSII (maximum quantum yield of photosystem II) was very similar in all treatments. The two assayed PGPR strains triggered a significant increase in sugar beet production yield and quality. PGPRs inoculation techniques could be used in different crops and they could be applied as biofertilizers, improving the agricultural production.

SUMMARYDamping off is the most common disease caused by edaphic fungi in Spanish crops, among which Rhizoctonia solani AG-4 stands out. In the present work, two possible methods of control were evaluated, incorporation of different doses of organic matter (OM; obtained from strawberry crops) and Pseudomonas fluorescens as a plant growth promoting rhizobacteria (PGPR). The highest inhibition (43% less) against the pathogen was found in the assays that used 20 g of biofumigant/kg soil. Inoculation of the P. fluorescens strain (PGPR) did not protect against the pathogen. In addition, the microbial evolution during incubation with OM was studied. For this purpose, the bacterial and fungal catabolic profiles were determined (using Biolog Eco and FF plates, respectively) as well as bacterial counts of total aerobes, Pseudomonas sp. and aminocyclopropane-1-carboxylate (ACC)-degrading populations, during OM incorporation. This agro-technique produced changes in microbial catabolic community profiles, increasing bacterial metabolic activity and minimizing metabolic diversity of micro-organisms under control with and without pathogen. As for microbial counts, aerobic and ACC-degrading populations decreased while Pseudomonas sp. population increased with OM treatments.The OM amendment applied to control the damping off caused by R. solani is viable; it is more environmentally friendly and has a lower economic cost than chemical controls and, therefore, it could serve as a component in integrated-management programmes.