Minakshi Grover

Effect of plant growth promoting Pseudomonas spp. on compatible solutes, antioxidant status and plant growth of maize under drought stress

Drought is one of the major abiotic stresses affecting yield of dryland crops. Rhizobacterial populations of stressed soils are adapted and tolerant to stress and can be screened for isolation of efficient stress adaptive/tolerant, plant growth promoting rhizobacterial (PGPR) strains that can be used as inoculants for crops grown in stressed ecosystems. The effect of inoculation of five drought tolerant plant growth promoting Pseudomonas spp. strains namely P.entomophila strain BV-P13, P. stutzeri strain GRFHAP-P14, P. putida strain GAP-P45, P. syringae strain GRFHYTP52, and P. monteilli strain WAPP53 on growth, osmoregulation and antioxidant status of maize seedlings under drought stress conditions was investigated. Drought stress induced by withholding irrigation had drastic effects on growth of maize seedlings. However seed bacterization of maize with Pseudomonas spp. strains improved plant biomass, relative water content, leaf water potential, root adhering soil/root tissue ratio, aggregate stability and mean weight diameter and decreased leaf water loss. The inoculated plants showed higher levels of proline, sugars, free amino acids under drought stress. However protein and starch content was reduced under drought stress conditions. Inoculation decreased electrolyte leakage compared to uninoculated seedlings under drought stress. As compared to uninoculated seedlings, inoculated seedlings showed significantly lower activities of antioxidant enzymes, ascorbate peroxidase (APX), catalase (CAT), glutathione peroxidase (GPX) under drought stress, indicating that inoculated seedlings felt less stress as compared to uninoculated seedlings. The strain GAP-P45 was found to be the best in terms of influencing growth and biochemical and physiological status of the seedlings under drought stress. The study reports the potential of rhizobacteria in alleviating drought stress effects in maize.

Drought-tolerant plant growth promoting Bacillus spp.: effect on growth, osmolytes, and antioxidant status of maize under drought stress

Abstract In present study Bacillus spp. screened for drought tolerance could tolerate minimal water potential (-0.73 MPa) were evaluated for plant growth promoting properties at –0.73 MPa. Drought stress affected growth of isolates as indicated by increased intracellular free amino acids, proline, total soluble sugars, and exopolysaccharides. Drought-tolerant Bacillus spp. HYD-B17, HYTAPB18, HYDGRFB19, BKB30, RMPB44 identified as Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus thuringiensis, Paenibacillus favisporus, Bacillus subtilis based on 16S rDNA gene sequence were used to study the effect of inoculation on growth, osmolytes, antioxidant status. Inoculation increased plant biomass, relative water content, leaf water potential, root adhering soil/root tissue ratio, aggregate stability, decreasing leaf water loss. Bacillus spp. effect on osmoregulation increased proline, sugars, free amino acids and decreased electrolyte leakage. Inoculation reduced the activity of antioxidant enzymes ascorbate peroxidase, catalase, glutathione peroxidase. As a result, Bacillus spp. inoculated maize seedlings showed physiological response that could alleviate drought stress negative effects.

Effect of inoculation with a thermotolerant plant growth promoting Pseudomonas putida strain AKMP7 on growth of wheat (Triticum spp.) under heat stress

The present study was carried out to investigate the effect of plant growth promoting thermotolerant Pseudomonas putida strain AKMP7 on the growth of wheat plants to heat stress. The results indicated the superior performance by P. putida strain AKMP7 in improving survival and growth of wheat plants under heat stress. The bacterium significantly increased the root and shoot length, dry biomass, tiller, spike let and grain formation of wheat over uninoculated plants. Inoculation reduced membrane injury and the activity of several antioxidant enzymes such as SOD, APX and CAT under heat stress. Inoculation improved the levels of cellular metabolites like proline, chlorophyll, sugars, starch, amino acids, and proteins compared to uninoculated plants. Scanning electron microscopy studies confirmed the colonization of the organism on the root surface. This result suggests the possible role of microorganisms in mitigating adverse effects of climate changes on crop growth and may lead to development of microbe based climate- ready technology.

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

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.

Characterization of rhizobial isolates nodulating Millettia pinnata in India

Millettia pinnata (Synonym Pongamia pinnata) is a viable source of oil for the mushrooming biofuel industry, source for agroforestry, urban landscaping, and the bio-amelioration of degraded lands. It also helps in maintaining soil fertility through symbiotic nitrogen fixation. However, not much work is reported on classification and characterization of the rhizobia associated with this plant. In the present study, an attempt was made to isolate rhizobial strains nodulating Millettia from soils collected from southern regions of India. The isolates were characterized using numerical taxonomy, 16S rRNA gene sequencing, and cross nodulation ability. The results showed high phenotypic and genetic diversity among the rhizobia symbiotic with Millattia pinnata. The isolates formed five clusters at similarity level of 0.82 based on the results of numerical taxonomy. Results on 16S rRNA gene sequence analysis revealed that most microsymbionts of M. pinnata belonged to Rhizobium and Bradyrhizobium, which are closely related to Rhizobium sp., B. elkanii and B. yuanmingense. Among these isolates, some isolates could grow in a pH range of 4.0-10.0, some could tolerate a high salt concentration (3% NaCl) and could grow at a maximum temperature between 35 and 45 °C. M. pinnata formed nodules with diverse rhizobia in Indian soils. These results offered the first systematic information about the microsymbionts of M. pinnata grown in the soils from southern part of India.

Exploiting Plant Growth Promoting Rhizomicroorganisms for Enhanced Crop Productivity

The increasing pressure on land resources has made it imperative for vertical growth through enhanced crop intensity and productivity. To meet this challenge, appropriate integrated nutrient and pest management packages must be configured for different agro-ecological conditions. By 2050, the crop nitrogen demand is expected to reach 40–45 million tonnes. To meet such enormous nitrogen requirements through chemical fertilizers, would not only be expensive but also could severely degrade soil health. Similar is the situation with other macro- and micro-nutrients. The rhizosphere environment, at the interface between root and soil, is a major habitat for soil processes. Rhizosphere biology is approaching a century of investigations, wherein growth-promoting rhizomicroorganisms such as Rhizobium, Azotobacter, Pseudomonas, Bacillus, Azospirillum, Frankia and mycorrhizal fungi have attracted special attention on account of their beneficial activities. Plant growth promoting rhizomicroorganisms (PGPR) include diverse microbes that influence plant health by colonizing roots, enhancing plant growth, reducing plant pathogen populations and activating plant defenses against biotic stresses. PGPRs promote plant growth in different ways such as influencing plant hormonal balance, antagonistic to pathogens through various modes, stimulation of plant resistance/defense mechanisms, effects nutrient uptake by secretion of organic acids or protons to solubilize nutrients, atmospheric N2 fixation and by modifying rhizospheric soil environment by exo-polysaccharides production. Though research was going on in isolation in the above areas, with the advent of a core group for PGPR research, the pace in this direction has significantly increased. The primary emphasis on exploiting the vast biodiversity of microorganisms to identify the beneficial strains has yielded very good results. However, most of the research is yet to reach the end-users. For effective transfer of these technologies, there is a need for functional networking of research, industry and extension systems. In this paper, we describe the recent advances in PGPR research and the future needs to strengthen PGPR research and development that will transfer the benefits to the end-users for enhanced and sustainable farm productivity hence contributing towards food security challenges.

Can microbes help crops cope with climate change

Agriculture is considered to be one of the most vulnerable sectors to climate change. The average temperature in the Indian sub-continent has risen by 0.57°C in the last 100 years and models project that it is likely to rise further to a maximum of 2.5°C by 2050 and 5.8°C by 2100. Besides high temperature, elevated CO 2 , extreme rainfall events, more fl oods, cyclones, cold waves, heat waves and frost are other effects likely to be witnessed as a result of global warming. The irrigation requirement of crops in arid and semi-arid regions is estimated to increase by 10% for every 1°C rise in temperature. These factors are likely to cause serious negative impacts on crop growth and yields and impose severe pressure on our land and water resources. Worldwide, extensive research is being carried out on crop and livestock systems for coping with climate change through development of heat- and drought-tolerant varieties, shifting the crop calendars, resource management practices such as zero tillage, improved methods of water harvesting and irrigation effi ciencies etc. While most of these technologies are cost-intensive, recent studies indicate microorganisms can also be used to help crops cope with climate change in a cost-effective manner [1]. The most important abiotic stress factors that infl uence crops due to climate change include drought, heat wave, cold wave, chilling injury and fl ooding. Rhizosphere and endorhizosphere microorganisms are reported to help plants tolerate these abiotic stresses by a variety of mechanisms including modifi cation of plant response at the gene level. Timmusk and Wanger (1999) were the fi rst to show that inoculation of Paenibacillus polymyxa confers drought tolerance in Arabidopsis thaliana through induction of a drought responsive gene ERD15 [2]. Last decade saw an explosion of publications reporting the benefi cial effects of microorganisms such as Pseudomonas, Bacillus, Arthrobacter, Pantoea, Burkholderia, Rhizobium etc. in enhancing the tolerance of crops such as sunfl ower, maize, wheat, chickpea, groundnut, spices and grapes to drought, salinity, heat stress and chilling injury under controlled conditions [3, 4]. The introduced microorganisms in the rhizosphere enhance soil aggregation by production of EPS thereby improving the water availability to plants during dry periods [5], induce the synthesis of heat shock proteins and osmoregulants such as proline, glycine betaine, help in maintenance of cell membrane integrity [6], all of which contribute to improved stress tolerance in plants. The introduced organisms also form biofi lms in the rhizosphere which protect plants from surrounding harsh environments. These researches open up new and exciting possibilities of utilizing microorganisms as inoculants for enhancing tolerance of plants to climate change induced abiotic stresses. These inoculants could form major component of the climate change ready technologies being developed globally to help agriculture and livestock production to cope with climate change. As many of such technologies are likely to have intellectual property value, this fi eld offers immense opportunities for young and active researchers.

Application of Microbiology in Dryland Agriculture

Microorganisms are key players in nutrient cycling and hence form important components of a soil ecosystem. Besides, improving nutrient availability, certain microorganisms also provide growth and health benefits to plants through direct and indirect mechanisms. Dryland soils are are poorly developed with low organic matter content and hence have poor water retention capacity. Besides, dryland soils face various abiotic stresses like nutrient imbalance, drought, heat etc. Application of organic based fertilizers improves the microbial populations and soil organic carbon. Cropping systems and residue management practices also influence microbial parameters in dryland soils. Increased abundance of microorganisms in dryland soil can help in improving soil aggregation and soil organic matter carbon content, thus increasing the water retention capacity of the soil. Besides, microbial inoculants with specific function such as nutrient solubilization and mobilization, plant growth promotion, disease control and abiotic stress management can be applied alone or in combination. Thus, the promotion of microbial-based technologies and/or the management practices that improve soil microbial parameters is important for the sustainability of dryland ecosystems.

Actinomycetes as Mitigators of Climate Change and Abiotic Stress

Agricultural productivity is affected worldwide due to anthropogenic and climate change-induced abiotic stresses, posing a threat to food security. Use of microorganisms for abiotic stress management in agriculture is emerging as economically viable and environmental-friendly option. Actinomycetes, the Gram-positive bacteria with filamentous structure that are common associates of plants (as rhizosphere inhabitants and as plant endophytes), are receiving attention for their potential application in stressed ecosystems. Many actinomycetes exhibit plant growth-promoting (PGP) properties including indole acetic acid (IAA) production, phosphate solubilization, siderophore production, biocontrol of phytopathogens, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity. Besides, they can grow under diverse stress conditions such as moisture stress, high temperature, salinity, alkalinity, and wide pH range. Recently, many reports have documented the role of actinomycetes in alleviating salinity and drought stress in crop plants. However, there is a need to further strengthen the research to explore their potential to improve plant productivity under diverse environmental stress conditions by conducting extensive pot and field trials and to understand the underlying mechanisms.