Abstract
The aim of the present study was to evaluate the impact of
Trichoderma harzianum
UBSTH-501- and methyl jasmonate-induced systemic resistance and their integration on the spot blotch pathogen,
Bipolaris sorokiniana
through enhanced phenylpropanoid activities in bread wheat (
Triticum aestivum
L.). It was found that the application of MeJA (>100 mg L
–1
) inhibits the germination of
B. sorokiniana
spores under controlled laboratory conditions. To assess the effect of MeJA (150 mg L
–1
) in combination with the biocontrol agent
T. harzianum
UBSTH-501
in vivo
, a green house experiment was conducted. For this, biocontrol agent
T. harzianum
UBSTH-501 was applied as seed treatment, whereas MeJA (150 mg L
–1
) was applied 5 days prior to pathogen inoculation. Results indicated that application of MeJA (150 mg L
–1
) did not affect the root colonization of wheat by
T. harzianum
UBSTH-501 in the rhizosphere. The combined application of
T. harzianum
UBSTH-501 and MeJA also enhanced indole acetic acid production in the rhizosphere (4.92 μg g
–1
of soil) which in turn helps in plant growth and development. Further, the combined application found to enhance the activities of defense related enzymes
viz.
catalase (5.92 EU min
–1
g
–1
fresh wt.), ascorbate peroxidase [μmol ascorbate oxidized (mg prot)
–1
min
–1
], phenylalanine ammonia lyase (102.25 μmol cinnamic acid h
–1
mg
–1
fresh wt.) and peroxidase (6.95 Unit mg
–1
min
–1
fresh wt.) significantly in the plants under treatment which was further confirmed by assessing the transcript level of
PAL
and
peroxidase
genes using semi-quantitative PCR approach. The results showed manifold increase in salicylic acid (SA) along with enhanced accumulation of total free phenolics, ferulic acid, caffeic acid, coumaric acid, and chlorogenic acid in the leaves of the plants treated with the biocontrol agent alone or in combination with MeJA. A significant decrease in the disease severity (17.46%) and area under disease progress curve (630.32) were also observed in the treatments with biocontrol agent and MeJA in combination as compared to
B. sorokiniana
alone treated plant (56.95% and 945.50, respectively). Up-regulation of phenylpropanoid cascades in response to exogenous application of MeJA and the biocontrol agent was observed. It was depicted from the results that PAL is the primary route for lignin production in wheat which reduces cell wall disruption and tissue disintegration and increases suberization and lignification of the plant cell as seen by Scanning Electron microphotographs. These results clearly indicated that exogenous application of MeJA with
T. harzianum
inducing JA- and/or SA-dependent defense signaling after pathogen challenge may increase the resistance to spot blotch by stimulating enzymatic activities and the accumulation of phenolic compounds in a cooperative manner. This study apparently provides the evidence of biochemical cross-talk and physiological responses in wheat following MeJA and biocontrol agent treatment during the bio-trophic infection.
