G. D. Sharma

Consortium of Plant-Growth-Promoting Bacteria: Future Perspective in Agriculture

The term “plant-growth-promoting rhizobacteria” (PGPR) include soil bacteria that colonize the roots of plants following inoculation onto seed and enhance plant growth. The bacteria useful to plants were proposed to be characterized in two general types: bacteria forming a symbiotic relationship with the plant and another the free-living ones found in the soil but are often found near, on, or even within the plant tissues. The PGPR are known to enhance growth by several direct mechanisms—like biofertilizers fix nitrogen, phytostimulators directly promote the growth of plants by the production of hormones, and several other metabolites like siderophore, ACC deaminase, etc., are produced by PGPR strains for plant growth enhancement. Also, biocontrol agents that are able to protect plants from soilborne infection by deleterious microorganisms also offer environment-friendly strategy for pest control. Recently, application of two or more PGPR as consortium is taking gain in field application worldwide. This offers multifarious approach of promoting plant growth and improve yield. In this review, the various strategies for consortium formulation are described. In fact, use of rhizobia with free-living nitrogen fixers or with phosphate solubilizers including VAM fungi has been widely reported. Also, application of biocontrol agents along with direct growth promoters is also observed as holistic approach for sustainable agriculture. Further, tailor-made consortium is sometimes designed to include other benefits like improving soil health.

The Endophytic Symbiont—Pseudomonas aeruginosa Stimulates the Antioxidant Activity and Growth of Achyranthes aspera L.

A plant growth promoting bacterial endophyte designated as AL2-14B isolated from the leaves of Achyranthes aspera L. was identified as Pseudomonas aeruginosa based on its phenotypic and physiological features, and 16S rRNA gene sequence analysis. AL2-14B had plant growth stimulating attributes including siderophore and indole acetic acid release, inorganic phosphate solubilization, along with nitrogenase, ammonification, and protease activities. It also exhibited antifungal property against Rhizoctonia solani. The plantlets grown in germ-free condition were inoculated with AL2-14B and studied for the colonization of endophyte. Significant increase in population of AL2-14B between 3rd and 5th days after inoculation was recorded. The treatment of plants with endophytic P. aeruginosa AL2-14B increased nitrogen, phosphorus, potassium (NPK) contents in plant by 3.8, 12.59, and 19.15%, respectively. Significant enhancement of shoot and root length, dry leaf, dry shoot and dry root weight, and leaf surface area as compared to control (P < 0.05) was recorded in AL2-14B inoculated plants. The antioxidant activities increased in plants grown in germ-free conditions and inoculated with AL2-14B. The present study emphasizes on the role of diazotrophic endophyte P. aeruginosa AL2-14B in stimulating growth of A. aspera L. and improvement of its medicinal properties. Significant increase in growth and antioxidant content of P. aeruginosa AL2-14B treated plants suggests the possibility of an economical and eco-friendly mean of achieving antioxidants rich, healthier A. aspera plants.

The Vesicular Arbuscular Mycorrhiza Associated with Three Cultivars of Rice (Oryza sativa L.)

The present study deals with the occurrence of vesicular arbuscular mycorrhizal fungi in three cultivars of rice in Barak valley. Three cultivars of rice were Pankaj, Malati and Ranjit. The results revealed the association of VAM fungi in all the cultivars of rice. The association was maximum in Pankaj cultivar followed by Malati, and Ranjit, respectively, in all the three sampling phases. All the three cultivars of rice crop showed maximum soil spore population and number of VAM fungal species at the harvesting phase (135 DAS) and minimum at the phase of maturation (90 DAS). Glomus species were found dominating followed by Acaulospora species. Glomus microcarpum, Glomus claroideum, Glomus mosseae and Acaulospora scrobiculata were found in all the three fields.

Application of Bacillus spp. for Sustainable Cultivation of Potato (Solanum tuberosum L.) and the Benefits

Potato is a staple crop in 130 countries worldwide, ranking fourth in production after rice, maize, and wheat. It is also an important crop which holds promise for food to millions of people especially in developing countries. But the production of potato is hindered by many phytopathogenic fungal and bacterial diseases that cause considerable loss to potato production in field. Plant growth-promoting rhizobacteria (PGPR) colonize plant roots and induce an increase in plants growth. Among the mechanisms by which PGPR exert beneficial effects on plants are facilitating the uptake of nutrients such as phosphorus via phosphate solubilization, synthesizing stimulatory phytohormones like indole-3-acetic acid (IAA). Bacillus is one of the most commonly reported PGPR genera, as it has the advantage of being able to form endospores which confers them high stability as biofertilizers or biofungicides, which are resistant to heat, desiccation, organic solvents, and UV irradiation, and to produce various biologically active metabolites in addition to their abundance in soil. The ability to produce cell wall-degrading enzymes like protease, chitinase, and s-1,3-glucanase and the production of secondary metabolites such as siderophore are other important criteria for understanding the mechanism responsible for biological control attributes of these organisms. Other mechanisms like competition for nutrients and induction of systemic resistance in plants are also involved. In spite of the benefits, application of Bacillus in potato cultivation is not well established. In this article, application of Bacillus for the management of potato diseases, and other benefits with potential for use in the future to improve potato crop, has been discussed.