A. A. Joshi

Bio: A. A. Joshi is an academic researcher from Goa University. The author has contributed to research in topics: Rhizobacteria & Bacterial wilt. The author has an hindex of 1, co-authored 2 publications receiving 130 citations.

Pseudomonads: major antagonistic endophytic bacteria to suppress bacterial wilt pathogen, Ralstonia solanacearum in the eggplant ( Solanum melongena L.)

Abstract: Endophytic bacteria of eggplant, cucumber and groundnut were isolated from different locations of Goa, India. Based on in vitro screening, 28 bacterial isolates which effectively inhibited Ralstonia solanacearum, a bacterial wilt pathogen of the eggplant were characterized and identified. More than 50% of these isolates were Pseudomonas fluorescens in which a vast degree of variability was found to exist when biochemical characteristics were compared. In greenhouse experiments, the plants treated with Pseudomonas isolates (EB9, EB67), Enterobacter isolates (EB44, EB89) and Bacillus isolates (EC4, EC13) reduced the wilt incidence by more than 70%. All the selected isolates reduced damping off by more than 50% and improved the growth of seedlings in the nursery stage. Most of the selected antagonists produced an antibiotic, DAPG, which inhibited R. solanacearum under in vitro conditions and might have been responsible for reduced wilt incidence under in vivo conditions. Also production of siderophores and IAA in the culture medium by the antagonists was recorded, which could be involved in biocontrol and growth promotion in crop plants. From our study we conclude that Pseudomonas is the major antagonistic endophytic bacteria from eggplants which have the potential to be used as a biocontrol agent as well as plant growth-promoting rhizobacteria. Large scale field evaluation and detailed knowledge on antagonistic mechanism could provide an effective biocontrol solution for bacterial wilt of solanaceous crops.

Potential rhizobacteria for the suppression of bacterial wilt pathogen, Ralstonia solanacearum in eggplant (Solanum melongena L.)

Abstract: Study was conducted to select potential antagonistic rhizobacteria for the management of bacterial wilt in eggplant. Sixteen rhizobacterial isolates were selected based on their inhibition efficiency against R. solanacearum. Among the selected isolates, 75 per cent belonged to species of Pseudomonas, which was clustered into five phylogeny groups based on biochemical tests. Efficiency of disease suppression was tested in vivo under greenhouse conditions. The lowest wilt incidence (13.3%) was recorded in RC24 (P. putida) followed by RBh1 (B. sublitis- 20.0%). From the 16 isolates, eight were selected and tested for their efficacy in the field conditions by soil drenching in one month-old transplanted eggplants using talc based formulation. Though antagonist treatments reduced disease incidence, the biocontrol efficiency was less than 36 per cent. This indicates that the biocontrol treatments to be started right from sowing or planting. All the selected antagonists produced Indole Acetic Acid and siderophores, which are responsible for plant growth promotion and few of them produced 2, 4-diacetyl phloroglucinal, an antifungal antibiotic, indicating that these rhizobacteria would be highly effective to control R. solani when applied at right time.

Inside the root microbiome: Bacterial root endophytes and plant growth promotion

Abstract: Bacterial root endophytes reside in a vast number of plant species as part of their root microbiome, with some being shown to positively influence plant growth. Endophyte community structure (species diversity: richness and relative abundances) within the plant is dynamic and is influenced by abiotic and biotic factors such as soil conditions, biogeography, plant species, microbe-microbe interactions and plant-microbe interactions, both at local and larger scales. Plant-growth-promoting bacterial endophytes (PGPBEs) have been identified, but the predictive success at positively influencing plant growth in field conditions has been limited. Concurrent to the development of modern molecular techniques, the goal of predicting an organism's ability to promote plant growth can perhaps be realized by more thorough examination of endophyte community dynamics. This paper reviews the drivers of endophyte community structure relating to plant growth promotion, the mechanisms of plant growth promotion, and the current and future use of molecular techniques to study these communities.

Endophytic Microbes in Crops: Diversity and Beneficial Impact for Sustainable Agriculture

Abstract: Endophytic microbes are ubiquitous in most plant species. Endophytic microbes enter plants mainly through wounds, naturally occurring as a result of plant growth or through root hairs and at epidermal conjunctions. Besides gaining entrance to plants through natural openings or wounds, endophytic microbes appear to actively penetrate plant tissues using hydrolytic enzymes like cellulase and pectinase. Diverse community structure of endophytes can be analyzed using culture-dependent and culture-independent method. Endophytic bacteria belong to different phyla such as Acidobacteria, Actinobacteria, Ascomycota, Bacteroidetes, Basidiomycota, Deinococcus-Thermus, and Firmicutes. Endophytic archaea (Euryarchaeota) were reported using only culture-independent method. Endophytic microbes were most predominant and studied and belonged to three major phyla Actinobacteria, Proteobacteria, and Firmicutes. Among reported genera Achromobacter, Bacillus, Burkholderia, Enterobacter, Herbaspirillum, Pantoea, Pseudomonas, Rhizobium, and Streptomyces were dominant in most host plants. Along with common endophytic microbial genera, there were many niche-specific microbial genera that have been reported from different host plants. Application of associative microbes for sustainable agriculture holds immense potential. Endophytic microbes are known to enhance growth and yield of plants by fixing atmospheric nitrogen and solubilization of phosphorus, potassium, and zinc; production of phytohormones (cytokinins, auxins, and gibberellins), ammonia, hydrogen cyanide, and siderophores; and possession of antagonistic activity as well as reducing the level of stress ethylene in host plants. Endophytes seem to contribute to plant fitness and development, displaying beneficial traits that can be exploited in agricultural biotechnology. The interactions between endophytes and plants can promote plant health and play a significant role in low-input sustainable agriculture for both food and nonfood crops. This chapter summarizes part of the work being done on endophytic microbes, including their isolation, identification, diversity, distribution, and applications for sustainable agriculture.

Diversity of endophytic bacteria in ginseng and their potential for plant growth promotion.

Abstract: Endophytic bacteria have been found in virtually every plant studied, where they colonize the internal tissues of their host plant and can form a range of different beneficial relationships. The diversity of bacterial endophytes associated with ginseng plants of varying age levels in Korea was investigated. Fifty-one colonies were isolated from the interior of ginseng stems. Although a mixed composition of endophyte communities was recovered from ginseng based on the results of 16S rDNA analysis, bacteria of the genus Bacillus and Staphylococcus dominated in 1-year-old and 4-year-old plants, respectively. Phylogenetic analysis revealed four clusters: Firmicutes, Actinobacteria, α-Proteobacteria, and γ-Proteobacteria, with Firmicutes being predominant. To evaluate the plant growth promoting activities, 18 representative isolates were selected. Amplification of nifH gene confirmed the presence of diazotrophy in only two isolates. Half of the isolates solubilized mineral phosphate. Except four, all the other endophytic isolates produced significant amounts of indole acetic acid in nutrient broth. Iron sequestering siderophore production was detected in seven isolates. Isolates E-I-3 (Bacillus megaterium), E-I-4 (Micrococcus luteus), E-I-8 (B. cereus), and E-I-20 (Lysinibacillus fusiformis) were positive for most of the plant growth promoting traits, indicating their role in growth promotion of ginseng.