Responses of hydroponically-grown common bean to N-starvation combined by root inoculation with N2-fixing bacteria

C.K. Kontopoulou, S. Giagkou, E. Stathi, D. Savvas, P.P.M. Iannetta
Rhizobia inoculants contribute to increased N-fixation and yield in legume crops. Common bean (Phaseolus vulgaris) is widely cultivated not only in the soil but also on substrates to produce green pods consumed as vegetables. However, the impact of Rhizobium inoculation on plant nutrition and yield performance in hydroponically-grown beans has been hardly investigated up to date. In this research, common bean grown on an inert medium (pumice) was inoculated with either Rhizobium tropici CIAT899 or a commercial product containing a mixture of N-fixing bacteria, specifically Rhizobium sp. and Azotobacter sp. The plants treated with both inoculants were supplied with an N-free nutrient solution throughout the cropping period. A third treatment with non- inoculated plants, which were supplied with a standard nutrient solution containing N, was applied as control. Inoculation with R. tropici raised significantly the total number of root nodules in comparison with the other two treatments. The supply of N-free solution restricted appreciably both total plant biomass and pod yield while the inoculation with Rhizobium tropici mitigated this effect. The above-ground tissues of plants fed with N-free nutrient solution contained appreciably less N than those fed with standard solution when they were inoculated with the commercial inoculant. However, the supply of N-free nutrient solution did not decrease the N concentration in the above-ground tissues when the bean plants were inoculated with Rhizobium tropici. Furthermore, the supply of an N-free nutrient solution restricted appreciably the K levels in the above-ground plant biomass, regardless of Rhizobium inoculation treatment.
Kontopoulou, C.K., Giagkou, S., Stathi, E., Savvas, D. and Iannetta, P.P.M. 2016. Responses of hydroponically-grown common bean to N-starvation combined by root inoculation with N2-fixing bacteria. Acta Hort. (ISHS) 1142:31-36
nutrient uptake, Phaseolus, soilless culture, N2-fixation, pumice

Acta Horticulturae