Evidence that fresh weight measurement is imprecise for reporting the effect of plant growth-promoting (rhizo)bacteria on growth promotion of crop plants

Eight greenhouse experiments were performed to compare the effect of seven plant growth-promoting (rhizo)bacteria (PGPR/PGPB) on fresh and dry weights of four crop plants. This has been done to validate if fresh weight measurements of plant variables can serve as reliable values when reporting the effect of these bacteria on plant growth. These experiments show that the growth promotion effects by the tested PGPR/PGPB, including Bacillus amyloliquefaciens GB03, Bacillus subtilis IN-937B, Bacillus altitudinis INR7, and Pseudomonas mandelii 89B-27 in corn and cucumber and Azospirillum brasilense Cd, A. brasilense Sp 245, and Azospirillum lipoferum Br 17 in pepper and tomato, varied significantly between fresh and dry weights of shoot, root, and/or whole plant in the repeated greenhouse experiments. These results support our hypothesis that using fresh weight determination for assessing plant growth promotion by beneficial bacteria is inherently faulty. Therefore, it is recommended that dry weight determination rather than fresh weight determination is used for plant growth promotion tests.