262 V. K. Lingaraj et al.
Introduction
The Asian rice gall midge, Orseolia oryzae
(Wood-Mason) (Diptera: Ceceidomyiidae), is
a major insect pest of rice in Asia (Bentur et al.
2003 ). In India, gall midge has been reported
from almost all the rice growing states except
Western Uttar Pradesh, Uttarakhand, Punjab,
Haryana and the hill states of Himachal Pradesh
and Jammu and Kashmir (Bentur et al. 1992 ).
The insect being endoparasitic, use of resistant
varieties is the most economical and feasible tool
for its suppression (Heinrichs and Pathak 1981 ;
Khush 1997 ; Mathur et al. 1999 ). But the emer-
gence of new virulent biotypes of gall midge in
popular rice varieties is capable of overcoming
resistance and this is a cause for concern. To
date six biotypes of gall midge were identified
and characterized in India (Bentur et al. 2003 ).
Widespread cultivation of high-yielding variet-
ies made a radical change in the pest status of
rice gall midge in coastal Karnataka. In the past
few years, rice growers faced a substantial loss in
yield because of this pest.
A wide range of allelochemical compounds
present in the plants play an important defensive
role against insects and other herbivores. Several
instances of associations have been reported be-
tween phenolics and the resistance of plants to
insect damage (Panda and Khush 1995 ). Proline
is a basic amino acid found in high percentage in
basic protein. Free proline is said to play a role in
plants under stress conditions (Singh et al. 1972 ;
Blum and Ebercon 1976 ). Though the molecular
mechanism has not yet been established for the
increased level of proline, one of the hypotheses
refers to the breakdown of proteins into amino
acids and conversion to proline for storage. Many
workers have been reported a severalfold increase
in the proline content under entomological, path-
ological and other physiological stress conditions
(Mohanty and Sridhar 1982 ; Roy et al. 1988 ). In-
dole acetic acid (IAA) is an important hormone
involved in plant growth and development. As
this phytohormone is intimately involved in the
biochemical, physiological and genetic functions
of plants under stress conditions (Balasubrama-
nian and Purushothaman 1971 ), information on
the exact amount of IAA is essential. Since the
gall was developed upon infestation by the gall
midge, the present investigation was made to
know the changes in phenols, free proline and
IAA profile due to infestation of gall midge.Material and Methods
Extraction
Un-infested vegetative shoot epics of 0.5 cm (ap-
prox.) from 30-day-old plants of test entries were
collected after stripling leaves and leaf sheaths.
Five replications were maintained for each geno-
type. The collected plant samples were thorough-
ly washed with distilled water and dried under
shade. One gram plant sample piece of all geno-
types were taken in separate conical flasks and
15 ml, 80 % ethanol, was added. It was refluxed
for 30 min on hot water bath. After boiling, the
extract was cooled and the pieces of tissues were
ground thoroughly in a mortar with pestle in
slight ethanol. The supernatant was decanted into
another flask and residue was re-extracted with
small quantity of hot ethanol and decanted. The
extract was filtered through Whatman No.1 filter
paper and made up to a known volume with 80 %
ethanol. The ethanol part of (alcoholic) extract
was stored in refrigerator at 4 °C and was used
for the estimation.V. K. Lingaraj ()
Department of Agricultural Entomology, College of
Agriculture, UAS (B), Visveswarayya Canal Farm,
Mandya, Karnataka, 571405 India
e-mail: [email protected]
A. K. Chakravarthy
Department of Agricultural Entomology, Gandhi Krishi
Vignan Kendra (GKVK), University of Agricultural
Sciences, Bangalore Karnataka 560065 India
S. U. Patil
Zonal Agricultural Research Station
(ZARS), Bramhavar, Karnataka, 576213 India