266 V. K. Lingaraj et al.
tible genotypes. In resistant genotypes this phe-
nomenon was not evident. On the third day after
infestation, the IAA content in susceptible geno-
types viz., Jaya, IR20 and TN 1 was 3.16, 3.56
and 3.78 μg/100 g, respectively, and it increased
to 7.46, 8.18 and 6.91 μg/100 g, respectively, on
the fifth day and 10.58, 11.26 and 10.86 μg/100 g
on the seventh day after infestation, respectively.
Thus, the rapid accumulation of IAA in relation
to insect infestation in susceptible genotypes
clearly indicated their role in gall formation be-
cause IAA acts as a growth regulator. In the phe-
nol profile studies there was a slight increase in
the level of phenols even in the susceptible geno-
types viz., Jaya, IR 20 and TN 1. This slight in-
crease in phenols acts as IAA-oxidase inhibitors
resulting in hyperauxinity in gall tissue on which
the gall midge feed.
As observed in the accumulation of proline in
susceptible genotypes, significantly higher ac-
cumulation of IAA levels on the third, fifth and
seventh day after infestation was observed in all
susceptible genotypes, while in the case of resis-
tant entries this phenomenon was not observed.
On the third day after infestation, the IAA con-
tent in susceptible genotypes such as Jaya, IR
20 and TN1 was 3.16, 3.56 and 3.78 μg/100 g,
respectively, and it was increased to 7.46, 8.18
and 6.91 μg/100 g on the seventh day after infes-
tation, respectively. Thus, the rapid accumulation
of IAA in relation to insect infestation in suscep-
tible genotypes in the present study clearly indi-
cated their role in gall formation because IAA
acts as a growth regulator.
The present investigation corroborates the
study by Balasubramanian and Purushothaman
( 1971 ) who also reported higher tryptophan and
IAA level in galled shoot than healthy tissues.
In the present study the increase in IAA level in
susceptible genotypes of rice might be attributed
to the release of IAA from IAA–protein com-
plex. The IAA might also have originated from
structural proteins by the action of proteolytic en-
zymes releasing a number of amino acids, includ-
ing proline. Similarly, the present phenol profile
study indicated the slight increase of phenols
even in susceptible genotypes due to gall midge
infestation. This slight increase in phenols acts
as IAA-oxidase inhebitors (Amudhan et al. 1999 )
which might have resulted in hyperauxinity due
to changes in the auxin level due to host parasite
interactions in the gall tissue on which the gall
midge feed.
Orseolia oryzae continues to be one of the
most important endemic pests of rice in Coastal
Karnataka. All cultivated rice varieties, either
local or released as resistant, have become sus-
ceptible during the past decade. Concomitantly,
the O. oryzae population has evolved into a com-
plex, embracing more than one biotype, i.e. the
genetically homogenous population has become
heterogeneous, rendering pest management dif-
ficult. This study has clearly revealed the bio-
chemical profile of selected rice genotypes and
induced resistance in these rice genotypes against
the rice gall midge damage.Acknowledgements We thank J.S. Bentur (AICRIP)
and I.C. Pasalu (DRR, Hyderabad). VK Lingaraj also
acknowledges a fellowship of the University Grants
Commission (UGC) sponsored by the Ministry of Social
Justice and Empowerment, Government of India (UGC
F.16-93/SA-II/RGNF/KAR-6/2005–06). Thanks are also
due to director of research, University of Agricultural
Sciences, Bangalore and to the farmers of southern and
coastal regions of Karnataka.References
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