Antixenosis and Antibiosis Component of Rice Resistance to Asian Rice ... 271
genotypes recording < 10 % seedling damage in
preliminary evaluation were selected for replicat-
ed tests. Only the genotypes recording no dam-
age in replicated tests were rated as resistant and
were used for studying mechanism of resistance.
After screening, the selected rice genotypes were
used for resistance studies.
Nature of Resistance
Antixenosis and antibiosis were studied together.
The test resistant and susceptible entries from
the trials, viz., gall midge screening trial (GMS)
and gall midge biotype trial (GMBT), National
screening trial 1 (NSN 1) were sown as row in
plastic trays (42 × 30 × 8 cm) with 2–3 cm from
plant to plant and 4 cm between rows. Each test
entry was represented by ten seedlings of 20 days
age in a tray, as replicate. Such four trays were
maintained as four replications. A day before in-
festation, the trays were covered with cage made
out of plastic sheets. From the stock culture, 20
female and 10 male adult gall midges were re-
leased on the test seedlings in each replication.
Thus, in the free choice test gall midges were al-
lowed to settle on test seedlings of the entries.
The number of adults settled on each entry after
6 h and the number of eggs laid on seedling of
the test entry 48 h after infestation were count-
ed using hand lens. Antibiosis was studied on
the same plants by recording maggot survival
through periodic dissection and recording the
number of surviving and dead insects at 7, 14,
and 18 days after release. The data obtained were
subjected to analysis of variance (ANOVA) and
means were separated by Duncan’s multiple
range test (DMRT) (Duncan 1955 ).
Results and Discussion
Nature of Resistance
Antixenosis
The results revealed that, significantly higher
number of adults ( P < 0.05) settled on suscep-
tible checks TN 1 (0.35 per plant) and Jaya (0.32
per plant) compared to resistant genotypes. For
instance, the number of adults that settled on JGL
13595, NDR 2063, Abhaya, and RDR 987 was
0.11, 0.11, 0.12, and 0.12 per plant, respectively,
and was on par with each other. However, on the
resistant genotypes, viz., RP 4647-1073, MTU
1075, and RP 4644-1183 recorded higher number
of adults after release besides showing resistance.
So no distinct antixenosis in terms of number of
adults settled was evident between resistant and
susceptible genotypes. But, significantly higher
number of eggs ( P < 0.05) were noticed on TN 1
(14.44 eggs per plant) and Jaya (13.10 eggs per
plant) compared to resistant genotypes. Among
the resistant genotypes, significantly lower eggs
were observed on RP 4613–260 (3.88 eggs per
plant) followed by OR 2093-4 (6.77 eggs per
plant). Likewise, the number of eggs on RP 4647-
1073, Abhaya, RDR 987, NDR 3110, RP 4644-
1183, MTU 1075, and OR 1914-8 was 8.33, 8.44,
8.77, 9.33, 9.44, 9.77, and 9.88, respectively, and
was on par with each other (Table 1 ).
Similarly, in 2006 wet, significantly higher
number of adults ( P < 0.05) settled on susceptible
check TN 1 and Jaya, which recorded 0.54 and
0.34 adults per plant, respectively, compared to
resistant genotypes. Among the resistant geno-
types, few adults were found on JGL 13376,
JGL 13418, JGL 11605, RP 4643-713, and JGL
11459 which recorded 0.05, 0.15, 0.21, 0.21, and
0.23 adults per plant, respectively, and differed
significantly ( P < 0.05) from each other. Thus,
distinct antixenosis in terms of number of adults
settled was noticed between resistant and sus-
ceptible genotypes. Maximum (23.21 and 16.33
eggs per plant) numbers of eggs were noticed on
susceptible checks TN1 and Jaya, and were sig-
nificantly higher ( P < 0.05) compared to resistant
genotypes. Likewise, the number of eggs laid by
the females on JGL 13418, RP 4643-713, JGL
11605, and OR 1967-15 was 4.33, 5.11, 5.44, and
5.44 eggs per plant, respectively, and they were at
par with each other. Thus, distinct ovipositional
preference was observed between the resistant
and susceptible genotypes (Table 2 ).
Earlier studies on the mechanism of resistance
to gall midge suggested the involvement of bio-
physical characters such as hairiness of leaf blade
or compactness of leaf sheath as a factor confer-
ring resistance (CRRI 1952 ; Israel et al. 1961 ;