Genetic and physiological relatedness of antagonistic Trichoderma isolates against soil borne plant pathogenic fungi

In this study, the in vitro potential of 42 Trichoderma spp. were evaluated against four isolates of soil borne phytopathogenic fungi viz., Rhizoctonia solani, Macrophomina sp., Sclerotium rolfsii and Pythium aphanidermatum in dual culture techniques and through production of volatile and non-volatile inhibitors. In vitro screening results showed that the proportion of isolates with antagonistic activities was highest for the S. rolfsii followed by R. solani, Macrophomina sp. and P. aphanidermatum, respectively. The isolates TNT1, TNP2 and TWP1 showed consistent results in volatile and non-volatile activity in vitro against any of the two pathogens tested. Based on genomic finger prints, potential isolates showed no particular correlation between the origin of the isolates and the Random Amplified Polymorphic DNA (RAPD) groups could not be established. However, the polymorphism shown by the isolates did not correlate to their level of antagonism. Whereas, in physiology studies using BIOLOG (microbial identification system), three groups were formed, one group consists with 14 different Trichoderma species and two groups with two isolates each comprised of only T. koningii and T. viride.     

Endophytic bacteria from tomato and chilli,their diversity and antagonistic potential against Ralstonia solanacearum

A total of 82 endophytic bacteria of tomato and chilli was isolated from different locations of tropical Islands of Andaman and Nicobar, India. Based on in vitro screening, 16 bacterial isolates that effectively inhibited Ralstonia solanacearum (a bacterial wilt pathogen) were characterised for their diversity and identified through Microbial Identification System (Biolog). Diversity analysed through BOX-PCR showed low similarity index among the antagonistic bacteria. Based on the in vitro antagonistic activities, the selected isolates were further characterised for siderophore, indole acetic acid production, phosphate solubilisation and other extracellular enzymes; it is found that most of the isolates were positive for these properties. The production of these metabolites may be responsible for the inhibition of the pathogen R. solanacearum. The isolates BECS3, BECS6 and BECS7 showed multiple attributes and demonstrated plant growth promotion properties through tomato- and chilli-based bioassay under greenhouse conditions. These bacterial inoculations were found to result in significant increase in root, shoot and biomass of both tomato and chilli. Hence, these isolates can be further formulated and used for field application.     

Isolation and characterization of rhizobacteria associated with coastal agricultural ecosystem of rhizosphere soils of cultivated vegetable crops

In this study, a total of 80 rhizobacteria was isolated from coastal agricultural ecosystem of cultivated vegetable rhizosphere soils. The isolates were screened for antagonistic activity against Sclerotium rolfsii and Colletotrichum capsici and plant growth promoting traits. The results revealed that 15.0 and 43.7% isolates showed statistically significant inhibition of mycelial growth of S. rolfsii and C. capsici respectively, while 48.7% isolates produced siderophore, 57.5% isolates solubilized phosphate and 21.1% isolates produced indole-3-acetic acid more than 20 μg/mL. However, only three isolates PfS1, PfR2 and BL5 were found positive to all properties tested. The identification of potential bacterial isolates through Microbial Identification System (BIOLOG) and 16S rDNA sequencing of the isolates revealed Bacillus species were dominant in the cultivated vegetable rhizosphere soil of Neil and Havelock Islands, India.     

Isolation and Characterization of Salt Tolerant Plant Growth Promoting Rhizobacteria from Plants Grown in Tsunami Affected Regions of Andaman and Nicobar Islands

In order to explore salt tolerant plant growth promoting rhizobacteria (PGPR), 121 isolates were recovered from Tsunami affected area of Andaman and Nicobar Islands, India, out of which 23 were grown at 10% NaCl. Out of total isolates grown at 10% NaCl concentration, 14 solubilized phosphate, 13 showed siderophore production, five showed Indole acetic acid (IAA) production and 16 produced one or more extra cellular enzymes. Isolates SJ10 and CR5 showed the highest enzyme production and PGP properties and five isolates showed antagonistic activity against Sclerotium rolfsii. Screening of potential isolates for nitrogen fixing gene (nifH) showed only three isolates (MM3, MM6 and MRC11) possessed nifH gene. Salt tolerant Bacillus PGPR could be used as a bio-inoculant to enhance the crop growth under Tsunami affected soils.     

Isolation and Characterization of Trichoderma spp. for Antagonistic Activity Against Root Rot and Foliar Pathogens

Trichoderma, soil-borne filamentous fungi, are capable of parasitising several plant pathogenic fungi. Twelve isolates of Trichoderma spp. isolated from different locations of South Andaman were characterized for their cultural, morphological and antagonistic activity against soil borne and foliar borne pathogens. The sequencing of these isolates showed seven different species. The isolates revealed differential reaction patterns against the test pathogens viz., Sclerotium rolfsii, Colletotrichum gloeosporioides and C. capsici. However, the isolates, TND1, TWN1, TWC1, TGD1 and TSD1 were most effective in percentage inhibition of mycelial growth of test pathogens. Significant chitinase and β-1,3-glucanase activities of all Trichoderma isolates has been recorded in growth medium. T. viride was found with highest chitinase whereas T. harzianum was recorded with highest β-1,3-glucanase activities.     

Inoculation of Cucumber (Cucumis sativus L.) Seedlings with Salt-Tolerant Plant Growth Promoting Bacteria Improves Nutrient Uptake,Plant Attributes and Physiological Profiles

Journal of Plant Growth Regulation - Salinity is one of the major abiotic stresses that cause retarded plant growth and crop production. It has been reported that harmful effects of salinity could...