Ameliorating the drought stress tolerance of a susceptible soybean cultivar, MAUS 2 through dual inoculation with selected rhizobia and AM fungus

Abstract

Background: Drought stress is currently the primary abiotic stress factor for crop loss worldwide. Although drought stress reduces the crop yield significantly, species and genotypes differ in their stress response; some tolerate the stress effect while others not. In several systems, it has been shown that, some of the beneficial soil microbes ameliorate the stress effect and thereby, minimizing yield losses under stress conditions. Realizing the importance of beneficial soil microbes, a field experiment was conducted to study the effect of selected microbial inoculants namely, N-fixing bacteria, Bradyrhizobium liaoningense and P-supplying arbuscular mycorrhizal fungus, Ambispora leptoticha on growth and performance of a drought susceptible and high yielding soybean cultivar, MAUS 2 under drought condition.

Results: Drought stress imposed during flowering and pod filling stages showed that, dual inoculation consisting of B. liaoningense and A. leptoticha improved the physiological and biometric characteristics including nutrient uptake and yield under drought conditions. Inoculated plants showed an increased number of pods and pod weight per plant by 19% and 34% respectively, while the number of seeds and seed weight per plant increased by 17% and 32% respectively over un-inoculated plants under drought stress condition. Further, the inoculated plants showed higher chlorophyll and osmolyte content, higher detoxifying enzyme activity, and higher cell viability because of less membrane damage compared to un-inoculated plants under stress condition. In addition, they also showed higher water use efficiency coupled with more nutrients accumulation besides exhibiting higher load of beneficial microbes.

Conclusion: Dual inoculation of soybean plants with beneficial microbes would alleviate the drought stress effects, thereby allowing normal plants' growth under stress condition. The study therefore, infers that AM fungal and rhizobia inoculation seems to be necessary when soybean is to be cultivated under drought or water limiting conditions.

Keywords: AM fungi; Ambispora leptoticha; Bradyrhizobium liaoningense; Dual inoculation.

Fig. 1

Response of soybean cultivar, MAUS 2 inoculated with Ambispora leptoticha + Bradyrhizobium liaoningense grown under irrigated and moisture stressed field conditions

Fig. 2

Influence of dual inoculation on a Relative water content, b Cell membrane damage and c Cell viability of leaves analyzed at flowering and pod filling stage of a drought susceptible soybean cultivar, MAUS 2 grown under irrigated and moisture stressed field conditions. Dual inoculation: Ambispora leptoticha + Bradyrhizobium liaoningense; UI un-inoculated, I inoculated, UIS un-inoculated stress, IS inoculated stress, Flowering stage: 1st stress period (35–60 DAS), Pod filling stage: 2nd stress period (85–100 DAS); Significant differences (p ≤ 0.05) relative to controls UI & UIS to their respective treatments I & IS are indicated by asterisk (*)

Fig. 3

Influence of dual inoculation on a leaf osmolyte content and b proline content of leaves at flowering and pod filling stage of a drought susceptible soybean cultivar, MAUS 2 grown under irrigated and moisture stressed field conditions. Dual inoculation: Ambispora leptoticha + Bradyrhizobium liaoningense; UI un-inoculated, I inoculated, UIS un-inoculated stress, IS  inoculated stress, Flowering stage: 1st stress period (35–60 DAS), Pod filling stage: 2nd stress period (85–100 DAS); Significant differences (p ≤ 0.05) relative to controls UI & UIS to their respective treatments I & IS are indicated by asterisk (*)

Fig. 4

Influence of dual inoculation on a guaiacol peroxidase (POX) activity and b super oxide dismutase (SOD) activity along with their respective native PAGE assays of leaf samples analysed at pod filling stage of a drought susceptible soybean cultivar, MAUS 2 grown under irrigated and moisture stressed field conditions. Dual inoculation: Ambispora leptoticha + Bradyrhizobium liaoningense; UI un-inoculated, I inoculated, UIS un-inoculated stress, IS inoculated stress, Pod filling stage: 2nd stress period (85–100 DAS); Significant differences (p  ≤ 0.05) relative to controls UI & UIS to their respective treatments I & IS are indicated by asterisk (*)

Fig. 5

Influence of dual inoculation on a specific leaf area and b total leaf area analysed at flowering and pod filling stage of a drought susceptible soybean cultivar, MAUS 2 grown under irrigated and moisture stressed field conditions. Dual inoculation: Ambispora leptoticha + Bradyrhizobium liaoningense; UI un-inoculated, I inoculated, UIS un-inoculated stress, IS inoculated stress, Flowering stage: 1st stress period (35–60 DAS), Pod filling stage: 2nd stress period (85–100 DAS); Significant differences (p  ≤ 0.05) relative to controls UI & UIS to their respective treatments I & IS are indicated by asterisk (*)