Internal Variability in Morphologically Identical Groups of Rhizobial Isolates.

Biological nitrogen fixation by the legume-rhizobia symbiosis is a major source of available N for agriculture. Obtaining new strains with greater potential for biological nitrogen fixation is one of the inoculant industry basis, and demands evaluation of a large number of strains. Four morphologically identical rhizobial groups were studied, with 54, 38, 31 and 14 isolates. These isolates were characterized for tolerance to salinity, acidity and aluminum and evaluated for FBN capacity. Variable tolerance to salinity was found at 15 g of NaCl L-1 within the group 3, but not among the remaining. Significant variability for shoot nitrogen content was found between the 154 strains, but only group 4 had significant intra-group differences for root dry mass, nitrogen content, and relative efficiency. Intra-group variability was not related to group size, since the smallest group showed the greatest variability. Examining the variation by forming non-different groups by Tukey test, the 10% significance level allowed finding a greater variation, with minimal Type I error. However, at this significance level, within groups variability is not consistent variable to variable. This indicates that it may be acceptable to work with a single representative from each 100% similarity level morphological groups, thereby reducing the number of treatments for an experiment and allowing the use of larger number of repetitions, and consequent reduction in random variation.