IDENTIFICATION OF DIFFERENTIALLY EXPRESSED TRANSCRIPTS IN GROUNDNUT CHALLENGED WITH Sclerotium rolfsii Sacc. CAUSING STEM ROT
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Date
2018
Authors
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Publisher
Acharya N.G. Ranga Agricultural University
Abstract
Stem rot mainly a soil-borne disease caused by Sclerotium rolfsii, is one
of the major constraints in groundnut production as it severely affects the yield
and quality of the produce. The present investigation was aimed for histopathological,
biochemical and identification of differentially expressed
transcripts in response to stem rot caused by Sclerotium rolfsii in groundnut. A
total of fifteen genotypes viz., ICGV 91114, ICGV 86590, ICGV 86031, ICGV
87160, ICGV 87157, ICGS 76, ICGS 44, ICGV 07132, ICGV 07072, CS19,
Dharani, Kadiri 6, Rohini, TCGS 1157 and Narayani were selected and
screened for stem rot resistance or tolerance in pot culture under artificial
conditions. Among these fifteen genotypes, ICGV 86590 found to be highly
tolerant as it has not shown any wilting symptoms even fifteen days after
inoculation with S. rolfsii and in contrast, Narayani found to be highly
susceptible with complete wilting and subsequent death of the plant.
The pot culture experiments were carried out in the glass house of
Regional Agricultural Research Station (RARS) and Molecular analysis at
Genomics lab, Institute of Frontier Technology (IFT), RARS, Tirupati. The
contrasting genotypes for stem rot viz., ICGV 86590 (tolerant) and Narayani
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(susceptible) were further analyzed for Scanning Electron Microscopy,
Biochemical and Molecular parameters at 24 hrs interval upto 4 days.
Scanning Electron Microscopy studies showed presence of distorted
xylem vessels with fungal mycelial growth in susceptible genotype, Narayani
at 72 HAI whereas in tolerant genotype, ICGV 86590 even at 72 HAI no
mycelial growth were observed in xylem vessels.
The accumulation of total phenol content was relatively increased by 2
folds in ICGV86950 at 96 hours after inoculation when compared to
susceptible genotype Narayani. The elevated levels of total phenols play an
important role in the resistance mechanism against infection with S.rolfsii in
tolerant groundnut genotype.
Chitinase activity was significantly increased 6 times more in
ICGV86590 at 96 hrs after challenged with S. rolfsii whereas in Narayani it
was almost constant throughout the sampling time in comparison with their
respective controls.
Peroxidase activity was induced as an early response to counter the
fungal pathogen attack and the infected tissue showed a higher activity of the
enzyme at 96 hrs after inoculation in tolerant genotype (1.87 min/gm/fresh
weight) when compared with susceptible genotype (0.42 min/gm/fresh weight).
β-1, 3-Glucanase activity was increased continuously at all sampling
intervals in both stem rot tolerant and susceptible genotypes in comparison
with their respective controls and was maximum in tolerant genotype ICGV
86590 at 96 hrs after S. rolfsii inoculation.
Polyphenol oxidase increased significantly upto 72 hrs after inoculation
in ICGV 86590 and slightly decreased at 96 hrs whereas in susceptible
genotype the polyphenol activity was slight increased throughout sampling
period.
To unravel the molecular mechanisms conditioning stem rot tolerance,
transcriptome was analyzed in groundnut subjected to S. rolfsii (0 to 96 hrs
after inoculation). To identify differentially expressed transcripts, cDNARAPD
analysis was carried out using total RNA collected from stem portion
near collar region from both unchallenged (control) and challenged
constrasting genotypes at 24 hrs interval upto 4 days.
To identify differentially expressed transcripts the transcriptome was
analyzed by cDNA-RAPD profiles in tolerant and susceptible groundnut
genotypes subjected to S. rolfsii. A total of 3485 Transcript Derived Fragments
(TDFs) were scored. Out of which 2137 TDFs were differentially expressed in
both resistant and susceptible genotypes challenged with S. rolfsii at 24 hrs
interval upto 4 days. Among the 2137 differentially expressed transcripts, 1471
transcripts exhibited qualitative difference and 666 transcripts displayed
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quantitative differences in banding pattern of cDNA-RAPD profiles among the
two groundnut genotypes.
The transcriptome data analyzed by cDNA-RAPD profiles can serve as
a valuable resource for gene discovery and the differentially expressed genes
can be cloned and further sequenced to reveal the function. Thus the identified
transcripts/genes can also be converted to functional markers and can be used
in marker assisted selection for stem rot resistance breeding.
Description
D5725
Keywords
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