ENHANCEMENT OF NODULATION AND PLANT GROWTH IN DRY BEAN BY INOCULATIONS WITH DIFFERENT MICROORGANISMS

Rhizobium etli (USDA 9032), two genetically modified strains, which originated from Rhizobium etli, and a plant growth-promoting-rhizobacterium, Azospirillum brasilense Sp7 either alone or in combination with the strain 9032 were inoculated into dry bean (Phaseolus vulgaris L.) to determine which inoculum yield the highest nodulation and plant growth. The experimental design was completely randomized design with 6 replications (pots) per treatment. Double inoculation with the strains Sp7 and 9032 yielded the highest nodule number and weight. While Sp7 significantly increased nodule number, it did not significantly increase nodule weight compared to the control. There was not a statistically significant difference among the treatment means in terms of nitrogen content. However, a genetically modified Rhizobium and the strain Sp7 significantly increased accumulations of nitrogen in shoots and whole plants, compared to the control. Consequently, the enhancement of nodulation does not always lead to higher plant nitrogen contents. In case of Azospirillum, there may be some additional explanation(s) (e.g. improved plant root system) for the increase in plant growth.