A simple method to evaluate the number of bradyrhizobia on soybean seeds and its implication on inoculant quality control.

Laboratorio de Fisiología Vegetal, Universidad Nacional de Rio Cuarto, Córdoba, Argentina. .
AMB Express 01/2011; 1(1):21. DOI: 10.1186/2191-0855-1-21
Source: PubMed

ABSTRACT Soybean seeds are non-sterile and their bacterial population interferes with the enumeration of beneficial bacteria, making it difficult to assess survival under different conditions. Within this context, the principal aims of this work were: (1) to improve a selective media for the enumeration of B. japonicum recovered from inoculated soybean seeds; (2) to establish the most representative mathematical function for B. japonicum mortality on soybean seeds after inoculation; (3) to evaluate if environmental or physiological conditions modify B. japonicum mortality on soybean seeds; and (4) to create a new protocol for quality control of soybean inoculants. We successfully evaluated the combination of pentachloronitrobenzene and vancomycin added to the yeast-mannitol medium to inhibit most fungi and Gram-positive soybean microbiota, thus producing reliable counts of B. japonicum from inoculated soybean seeds. Percentages of recovery and survival factors were obtained and used to construct a two-phase exponential decay non-linear regression function. High temperature and desiccation decreased these parameters, while the optimization of temperature and the use of osmoprotective compounds with inoculants increased them. The use of this protocol minimized heterogeneity between experiments and may be considered more reliable than the simple expression of direct colony count of bacteria recovered from seeds.

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    ABSTRACT: ABSTRACT: The authors regret that an error appears in Penna et al. (2011). The fourth sentence in the section Formulation and evaluation of the selective medium "This compound was initially solubilized in 98% ethanol, sterilized using 0.2 mum filters, added to 45degreesC YEM medium, and homogenized to obtain a final concentration of 0,2 g.l-1 of PCNB into the P-YEM medium. Must be replaced by the following "A solution of 10% PCNB in acetone, was diluted 1/5 in Tween 80 0,5%v/v in water, sterilized using 0.2 mum filters, added to 45degreesC YEM medium, and homogenized to obtain a final concentration of 0,04 g.l-1 of PCNB into the P-YEM medium".
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