Influence of Bacillus spp. strains on seedling growth and physiological parameters of sorghum under moisture stress conditions

Abstract

Microorganisms isolated from stressed ecosystem may prove as ideal candidates for development of bio-inoculants for stressed agricultural production systems. In the present study, moisture stress tolerant rhizobacteria were isolated from the rhizosphere of sorghum, pigeonpea, and cowpea grown under semiarid conditions in India. Four isolates KB122, KB129, KB133, and KB142 from sorghum rhizosphere exhibited plant growth promoting traits and tolerance to salinity, high temperature, and moisture stress. These isolates were identified as Bacillus spp. by 16S rDNA sequence analysis. The strains were evaluated for growth promotion of sorghum seedlings under two different moisture stress conditions (set-I, continuous 50% soil water holding capacity (WHC) throughout the experiment and set-II, 75% soil WHC for 27 days followed by no irrigation for 5 days) under greenhouse conditions. Plate count and scanning electron microscope studies indicated successful root surface colonization by inoculated bacteria. Plants inoculated with Bacillus spp. strains showed better growth in terms of shoot length and root biomass with dark greenish leaves due to high chlorophyll content while un-inoculated plants showed rolling of the leaves, stunted appearance, and wilting under both stress conditions. Inoculation also improved leaf relative water content and soil moisture content. However, variation in proline and sugar content in the different treatments under two stress conditions indicated differential effect of microbial treatments on plant physiological parameters under stress conditions.

Bacterial-mediated drought tolerance: Current and future prospects

“…The plant shoot length was also increased. Increases in shoot and plant growth under drought stress as a result of PGPR treatment have also been reported in other crops including sorghum (Sorghum bicolor L.) (Grover et al, 2014), sunflower (Helianthus annuus L.) (Castillo et al, 2013), wheat (Arzanesh et al, 2011;Kasim et al, 2013), green gram (Vigna radiata L.) (Saravanakumar et al, 2011) mung bean (Vigna radiata L.) (Sarma and Saikia, 2014) and maize Naseem and Bano, 2014;Naveed et al, 2014) (Table 1). Taken together, the above studies clearly show that treatment of plants with selected strains of PGPR leads to increase in shoot growth and improvements in plant growth which help plants tolerate drought stress.…”

“…This has been demonstrated in maize Vardharajula et al, 2011;Naseem and Bano, 2014), sorghum (Grover et al, 2014), potato plants (Gururani et al, 2013), mung bean (Sarma and Saikia, 2014), and Arabidopsis (Arabidopsis thaliana L.) (Cohen et al, 2015) (Table 1). For example, Wang et al (2012) reported that treatment of cucumber (Cucumis sativa L.) plants with a mixture of three PGPR strains (Bacillus cereus AR156, Bacillus subtilis SM21, and Serratia sp.…”

“…Several studies have shown that under drought stress, PGPR-treated plants maintained relatively higher RWC compared to non-treated plants, leading to the conclusion that PGPR strains that improve survival of plants under drought stress generally increase RWC in the plants. For example, Grover et al (2014) reported that sorghum plants treated with PGPR, Bacillus spp strain KB 129 under drought stress showed 24% increase in RWC over plants that were not treated with PGPR. Similar results have been demonstrated in maize Vardharajula et al, 2011;Bano et al, 2013;Naveed et al, 2014;Naseem and Bano, 2014) (Table 1).…”

Growth-promoting bacteria alleviates drought stress of G. uralensis through improving photosynthesis characteristics and water status

“…The mechanism of Bacillus spp. inoculation promoting growth and enhancing biotic or abiotic stress tolerance has been reported in many crops via different mechanisms (Vardharajula et al 2011;Grover et al 2014). Hawkes et al (2008) explained that increasing plant growth may be due to enhanced nutrient transfer to the host plant or altered carbon allocation pattern from plant to mycorrhiza.…”

Mitigation of drought stress effects on soybean gas exchanges induced by Azospirillum brasilense and plant regulators

“…Studies on plant growth promoting bacteria report a better use of water in inoculated plants, evidencing that the plant growth promoting bacteria help in the plant survival, because they maintain the highest relative water content (Grover et al 2014, Fan et al 2015. Accordingly, higher relative water content values represent plants with an advanced capacity of physiological adaptation to the environment, maintenance of cell division and physiological activity (Ngumbi & Kloepper 2016).…”