Coinoculation of Bradyrhizobium and Azospirillum to Mitigate the Effects of Drought Stress in Soybean Plants

Bacteria of the genus Azospirillum have been used to mitigate negative effects of drought stress. Since there is few information on interaction of new strains of A. brasilense and soil water status, we evaluated the effects of coinoculation of A. brasilense strains (Ab‐V5/Ab‐V6 and HM053) on soybean plants grown either with (40% of field capacity) or without (80% of field capacity) drought stress. A randomized complete block design in a 3 × 2 factorial scheme was used, and the treatments were replicated three times. Soybean seeds were initially inoculated with Bradyrhizobium strains SEMIA 5079 and SEMIA 5080, and then coinoculated with A. brasilense strains at a rate of 2 ml kg −1 of seeds for both inoculants. Assessments of gas exchange parameters, chlorophyl reading, nodulation, biomass production, and nutrient uptake by plants were performed 50 days after emergence. Drought stress negatively affected biomass production and nutrient uptake. Strains Ab‐V5/Ab‐V6 and HM053 did not improve soybean performance under drought stress. Coinoculation of soybean seeds with the ammonium‐excreting A. brasilense strain HM053 increased root density by 47% at 0–10 cm depth and 28% at 0–50 cm depth under suitable soil water supply. Increased plant rooting capacity in plants grown without drought stress and coinoculated with the strain HM053 might bring about important impacts on soybean agribusiness.