Efficacy of talc-based fornuilation of Pseudomonas fluorescens on the management of leaf spot disease of Stevia rebaudiana Bertoni
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Date
2014
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Abstract
Stevia rebaudiana Bertoni, *3 natural sweetener
contains two main sweetest compounds, stcyioside
(ST) and rebaudioside A (R-A), tasting about 300
and 450 times sweeter than sucrose, respectively.
I ’his commercially important plant also suffers a
leaf spot disease caused by thesfungus Alteniaria
alternata in various districts of Tamil Nadu, India.
In the present study, ten isolates o f fluorescent
pseudomonads were evaluated for their ability to
control leaf spot in stevia.^(Steviasrebaudiana
Bertoni). These isolates were characterized as
Pseudomonas fluorescens on,biochemical
tests. Among these isolates, P. fluorescens \so\a\e
AIJPF'6 .', and AUPF5 showed ’ the maximum
inhibition of mycelial gtovA)): o i Alternaria
alternata. They also increased plant growth in
stevia apart from reducing thedeaf spot incidence
under greenhouse condition. The isolates AUPF6
and AUPF5 were further tested for their ability to
iinduce production of defense’*related enzymes and,
■chemicals in" plants,'‘ Earlier ■■ and -increased^
activities of phenylalanine ammonia lyase (PAL),'
iperoxidase (PO) and polyphenol oxidase (PPO)
were observed in ■ P.. fluorescens AUPF6 and
AUPF5 pretreated stevia plants challenged with
Alternaria i alternata. Moreover, • higher
accumulation of phenolics was noticed in plants
ipretreated with P. fluorescens isolates AUPF6 and
AUPF5 challenged with Alternaria alternata .
Thus, the present study shows that in additionito
direct antagonism and plantsgrowth-prpinotion,
'induction of defense-related enzymes involved in
the phenyl •'‘propanoid pathway collectively
contributed to enhance resistance against^ithe
\maaion o f Alternaria alternata in sXcvia.