Studies on Rhizosphere-Bacteria mediated Biotic and Abiotic stress tolerance in Chickpea (Cicer arietinumL.)

A Plant Biostimulant from Ascophyllum nodosum Potentiates Plant Growth Promotion and Stress Protection Activity of Pseudomonas protegens CHA0

Abiotic stresses, including salinity stress, affect numerous crops, causing yield reduction, and, as a result, important economic losses. Extracts from the brown alga Ascophyllum nodosum (ANE), and compounds secreted by the Pseudomonas protegens strain, CHA0, can mitigate these effects by inducing tolerance against salt stress. However, the influence of ANE on P. protegens CHA0 secretion, and the combined effects of these two biostimulants on plant growth, are not known. Fucoidan, alginate, and mannitol are abundant components of brown algae and of ANE. Reported here are the effects of a commercial formulation of ANE, fucoidan, alginate, and mannitol, on pea (Pisum sativum), and on the plant growth-promoting activity of P. protegens CHA0. In most situations, ANE and fucoidan increased indole-3-acetic acid (IAA) and siderophore production, phosphate solubilization, and hydrogen cyanide (HCN) production by P. protegens CHA0. Colonization of pea roots by P. protegens CHA0 was found to be increased mostly by ANE and fucoidan in normal conditions and under salt stress. Applications of P. protegens CHA0 combined with ANE, or with fucoidan, alginate, and mannitol, generally augmented root and shoot growth in normal and salinity stress conditions. Real-time quantitative PCR analyses of P. protegens revealed that, in many instances, ANE and fucoidan enhanced the expression of several genes involved in chemotaxis (cheW and WspR), pyoverdine production (pvdS), and HCN production (hcnA), but gene expression patterns overlapped only occasionally those of growth-promoting parameters. Overall, the increased colonization and the enhanced activities of P. protegens CHA0 in the presence of ANE and its components mitigated salinity stress in pea. Among treatments, ANE and fucoidan were found responsible for most of the increased activities of P. protegens CHA0 and the improved plant growth.

Prospects for Abiotic Stress Tolerance in Crops Utilizing Phyto- and Bio-Stimulants

Environmental stressors such as salinity, drought, high temperature, high rainfall, etc. have already demonstrated the negative impacts on plant growth and development and thereby limiting productivity of the crops. Therefore, in the time to come, more sustainable efforts are required in agricultural practices to ensure food production and security under such adverse environmental conditions. A most promising and eco-friendly way to achieve this goal would be to apply biostimulants to address the environmental concerns. Non-microbial biostimulants such as humic substances (HA), protein hydrolysate, plant-based products and seaweed extracts (SWE), etc. and/or microbial inoculants comprising of plant growth-promoting microbes such as arbuscular mycorrhizal fungi (AMF), fluorescent and non-fluorescent Pseudomonas, Trichoderma spp., Bacillus spp. etc. have tremendous potentiality to enhance plant growth, flowering, crop productivity, nutrient use efficiency (NUE) and translocation, as well as enhancing tolerance to a wide range of abiotic stresses by modifying physiological, biological and biochemical processes of the crop-plants. Similarly, application techniques and timing are also important to achieve the desired results. In this article we discussed the prospects of using seaweed, microbial, and plant-based biostimulants either individually or in combination for managing environmental stresses to achieve food security in a sustainable way. Particular attention was given to the modifications that take place in plant's physiology under adverse environmental conditions and how different biostimulants re-program the host's physiology to withstand such stresses. Additionally, we also discussed how application of biostimulants can overcome the issue of nutrient deficiency in agricultural lands and improve their use efficiency by crop plants.

Amelioration of drought effects in wheat and cucumber by the combined application of super absorbent polymer and potential biofertilizer

Biofertilizer is a good substitute for chemical fertilizer in sustainable agriculture, but its effects are often hindered by drought stress. Super absorbent polymer (SAP), showing good capacity of water absorption and retention, can increase soil moisture. However, limited information is available about the efficiency of biofertilizer amended with SAP. This study was conducted to investigate the effects of synergistic application of SAP and biofertilizers (Paenibacillus beijingensis BJ-18 and Bacillus sp. L-56) on plant growth, including wheat and cucumber. Potted soil was treated with different fertilizer combinations (SAP, BJ-18 biofertilizer, L-56 biofertilizer, BJ-18 + SAP, L-56 + SAP), and pot experiment was carried out to explore its effects on viability of inoculants, seed germination rate, plant physiological and biochemical parameters, and expression pattern of stress-related genes under drought condition. At day 29 after sowing, the highest viability of strain P. beijingensis BJ-18 (264 copies ng^-1 gDNA) was observed in BJ-18 + SAP treatment group of wheat rhizosphere soil, while that of strain Bacillus sp. L-56 (331 copies ng^-1 gDNA) was observed in the L-56 + SAP treatment group of cucumber rhizosphere soil. In addition, both biofertilizers amended with SAP could promote germination rate of seeds (wheat and cucumber), plant growth, soil fertility (urease, sucrose, and dehydrogenase activities). Quantitative real-time PCR analysis showed that biofertilizer + SAP significantly down-regulated the expression levels of genes involved in ROS scavenging (TaCAT, CsCAT, TaAPX, and CsAPX2), ethylene biosynthesis (TaACO2, CsACO1, and CsACS1), stress response (TaDHN3, TaLEA, and CsLEA11), salicylic acid (TaPR1-1a and CsPR1-1a), and transcription activation (TaNAC2D and CsNAC35) in plants under drought stress. These results suggest that SAP addition in biofertilizer is a good tactic for enhancing the efficiency of biofertilizer, which is beneficial for plants in response to drought stress. To the best of our knowledge, this is the first report about the effect of synergistic use of biofertilizer and SAP on plant growth under drought stress.