Dhruva Kumar Jha
Gauhati University, Department of Botany, Faculty Member
Disease causes severe economic losses to agricultural crops. The loss due to disease should be controlled due to the rapid rise in demand of food. In recent years, biological control of plant pathogens has received increasing attention as... more
Disease causes severe economic losses to agricultural crops. The loss due to disease should be controlled due to the rapid rise in demand of food. In recent years, biological control of plant pathogens has received increasing attention as a promising supplement or alternative to chemical control. Biological control agent (BCA) inhibits the disease by using degradative enzymes, antibiotics, competition for nutrients and niches (CNN), siderophores, biosurfactants, detoxification and degradation of virulence factors of the pathogen, and by induced systemic resistance (ISR). Many bacterial species were found having disease-suppressive property in rice and maize along with the other agricultural crops, but Pseudomonas and Bacillus are the prominent one. There has been very limited work done on the biological means of disease management as compared to the tremendous unexplored biocontrol resources. An integrated rigorous research and investment in the field of disease management will brin...
ABSTRACT: The present in vitro study was carried out to screen such beneficial rhizobacterial isolates that could be utilised for improvement of growth of som plant (Persea bombycina Kost.), a primary food source of the muga silkworm.... more
ABSTRACT: The present in vitro study was carried out to screen such beneficial rhizobacterial isolates that could be utilised for improvement of growth of som plant (Persea bombycina Kost.), a primary food source of the muga silkworm. Rhizobacteria was isolated from the rhizospheric soil collected from the som germplasm conservation site located at Regional Muga Research Station, Central Silk Board, Boko, Assam (GPS location 25.990 N, 91.250 E). Sixty-one percent of the total 18 isolates showed phosphate solubilisation as well as NH3 production. On the contrary, fewer isolates (33%) produced Indole Acetic Acid in vitro. Majority of the isolates showed resistance to Penicillin and Vancomycin at concentrations >10mcg. In addition, some of the isolates depicted antagonistic activity against Pestalotiopsis disseminata and Phyllosticta persea, the two phytopathogens responsible for causing grey blight and leaf spot diseases respectively in P. bombycina. Molecular identification of two...
Fungal endophytes are microorganisms that grow inside living plant tissues without causing disease symptoms. They may establish symbiotic or mutualistic relationship with their respective hosts. Endophytes have been found in every plants... more
Fungal endophytes are microorganisms that grow inside living plant tissues without causing disease symptoms. They may establish symbiotic or mutualistic relationship with their respective hosts. Endophytes have been found in every plants studied so far and are to be found in virtually every plant on earth. Therefore, they are important constituent of microbial diversity. Endophytes are rich sources of functional metabolites because of their ability to produce good number of new and interesting bioactive molecules, which are of pharmaceutical, industrial and agricultural importance. In the recent years, fungal endophytes have been studied and exploited for bioactivity. Some important bioactive substances discovered from fungal endophytes associated are taxol, campothecin, crytocandin, phomol and helvolic acid. One of the major problems facing the future of endophyte biology and natural product discovery is the rapid disappearance of plant diversity, which holds the greatest possible ...
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ABSTRACT Conversion of pristine forests to agricultural lands is one of the leading causes of biodiversity loss worldwide. To assess the impact of such forest disturbance on microbial diversity, we investigated the diversity of arbuscular... more
ABSTRACT Conversion of pristine forests to agricultural lands is one of the leading causes of biodiversity loss worldwide. To assess the impact of such forest disturbance on microbial diversity, we investigated the diversity of arbuscular mycorrhizal fungi (AMF) in the rich forests of Karbi Anglong hills of Assam, a biodiversity hotspot part of Indo-Burma region. AMF spore diversity was assessed in distinct study sites with different intensities of disturbances that encompassed a pristine undisturbed forest (UF), slash-and-burn field (SBF), and monoculture forest (MF). A total of 35 arbuscular mycorrhizal (AM) fungal species belonging to 9 genera were isolated. Species forming glomoid spores were dominant in all the three sites followed by acaulosporoid spores. Highest spore density was found in UF and lowest in MF. Multivariate analyses revealed similarity in UF and SBF. It was found that in MF, AMF diversity was significantly modified and reduced, resulting in an ecological degraded ecosystem. Our results show that natural UF and SBF contained similar and a high AM fungal diversity. The AM fungal diversity is not significantly affected by the slash-and-burn agricultural land use practices practised by the ethnic hilly tribes and, therefore, could be a component of a tropical forest “conservation-agriculture matrix.” Also because of the high generic and species diversity found, this region can be considered as AMF hotspot and a priority place for conservation.
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Cellulose decomposing microorganisms (CDMs) are important for efficient bioconversion of plant biomasses. To this end, we isolated seven fungal isolates (Aspergillus wentii, Fusarium solani, Mucor sp., Penicillum sp., Trichoderma... more
Cellulose decomposing microorganisms (CDMs) are important for efficient bioconversion of plant biomasses. To this end, we isolated seven fungal isolates (Aspergillus wentii, Fusarium solani, Mucor sp., Penicillum sp., Trichoderma harzaianum, Trichoderma sp.1 and Trichoderma sp.2) and three bacterial isolates (bacterial isolate I, II and III) from partially decomposed farm yard manure, rice straw and vermicompost, and evaluated them for decomposition of rice straw (Oryza sativa), Ipomoea camea and Eichhornia crassipes biomass. CDMs inoculation, in general, reduced the composting period by 14-28 days in rice straw, 14-34 days in Eichhornia and 10-28 days in Ipomoea biomass over control. Of the 10 CDMs tested, Mucor sp. was found to be the most effective as Mucor-inoculated biomass required minimum time, i.e. 84, 68 and 80 days respectively for composting of rice straw, Eichhornia and Ipomoea biomass as against 112, 102 and 108 days required under their respective control. CDMs inocula...
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Abstract Soil bacterial communities, which contain the highest level of prokaryotic diversity of any natural environment, are important for ecosystem functioning.Acultureindependent metagenomic approach was employed in the present... more
Abstract Soil bacterial communities, which contain the
highest level of prokaryotic diversity of any natural environment,
are important for ecosystem functioning.Acultureindependent
metagenomic approach was employed in the
present investigation to characterize the diversity of soil
bacterial community composition in five geochemically and
hydrologically different surface and subsurface soil habitats
of Brahmaputra valley, Assam, North-East India, an Indo-
Burma mega-biodiversity hotspot. The diversity of soil
bacterial community was determined through sequence
analysis of 16S–23S intergenic spacer regions (ISR). Polymerase
chain reaction (PCR) universal primers, 1406F
(50-TGYACACACCGCCCGT-30) and 155r (50-GGGTT
BCATTCRG-30) were used for amplification of 16S–23S
ribosomal DNA intergenic spacers of bacteria. Amplification
resulted in an intense array of PCR products approximately
ranging in size from 200 to 900 bp. Clear banding
patterns were observed in analysed samples using the primer
set in combination. A clear change in microbial ISR profile
was observed on visual analysis of gel electrophoresis profiles.
Fast alignment database searches of PCR amplicons of
16S–23S ISR sequence data revealed that the isolated
sequences resembled five major phylogenetic groups of
bacteria, namely a-, b- and c-subdivisions of Proteobacteria,
Acidobacterium and Comamonadaceae.
highest level of prokaryotic diversity of any natural environment,
are important for ecosystem functioning.Acultureindependent
metagenomic approach was employed in the
present investigation to characterize the diversity of soil
bacterial community composition in five geochemically and
hydrologically different surface and subsurface soil habitats
of Brahmaputra valley, Assam, North-East India, an Indo-
Burma mega-biodiversity hotspot. The diversity of soil
bacterial community was determined through sequence
analysis of 16S–23S intergenic spacer regions (ISR). Polymerase
chain reaction (PCR) universal primers, 1406F
(50-TGYACACACCGCCCGT-30) and 155r (50-GGGTT
BCATTCRG-30) were used for amplification of 16S–23S
ribosomal DNA intergenic spacers of bacteria. Amplification
resulted in an intense array of PCR products approximately
ranging in size from 200 to 900 bp. Clear banding
patterns were observed in analysed samples using the primer
set in combination. A clear change in microbial ISR profile
was observed on visual analysis of gel electrophoresis profiles.
Fast alignment database searches of PCR amplicons of
16S–23S ISR sequence data revealed that the isolated
sequences resembled five major phylogenetic groups of
bacteria, namely a-, b- and c-subdivisions of Proteobacteria,
Acidobacterium and Comamonadaceae.
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The effect of inoculum concentrations, temperature, relative humidity (RH), incubation period and leaf age on sporulation of Pestalotiopsis disseminata and the development of grey blight disease on som (Persea bombycina Kost.) were... more
The effect of inoculum concentrations, temperature, relative humidity (RH), incubation period and leaf
age on sporulation of Pestalotiopsis disseminata and the development of grey blight disease on som
(Persea bombycina Kost.) were studied in controlled environmental conditions. These factors had
a significant role on spore germination and germ tube development of P. disseminata, the causal organism
of the disease. The optimum inoculum concentration of the pathogen were found to be 1 107 spores ml1
for maximum infection percentage. A nonlinear relationship was found between temperature and
germination percentage of spores at a given relative humidity (RH). However, 25 C (2) temperature
and 70% RHwere the optimum parameters for better spore germination of the pathogen. Young leaves (leaf
no. 1e4 from the top) were more susceptible for development of the diseases in a controlled environment
than the older leaves. The germination of spores started at 8 h of incubation and gradually increased up to
20 h (maximum). The disease severity was favoured in the optimum range of temperature (25 2 C) and
RH (70%) which had a combined effect. These epidemiological parameters could help in the management
practices of the disease.
age on sporulation of Pestalotiopsis disseminata and the development of grey blight disease on som
(Persea bombycina Kost.) were studied in controlled environmental conditions. These factors had
a significant role on spore germination and germ tube development of P. disseminata, the causal organism
of the disease. The optimum inoculum concentration of the pathogen were found to be 1 107 spores ml1
for maximum infection percentage. A nonlinear relationship was found between temperature and
germination percentage of spores at a given relative humidity (RH). However, 25 C (2) temperature
and 70% RHwere the optimum parameters for better spore germination of the pathogen. Young leaves (leaf
no. 1e4 from the top) were more susceptible for development of the diseases in a controlled environment
than the older leaves. The germination of spores started at 8 h of incubation and gradually increased up to
20 h (maximum). The disease severity was favoured in the optimum range of temperature (25 2 C) and
RH (70%) which had a combined effect. These epidemiological parameters could help in the management
practices of the disease.