Central Rice Research Institute Annual report...2011-12

Strategic Research on Pathogens/Pest Population Dynamics, Crop Losses and Forecasting
Life table and virulence of rice planthoppers
and their management through induced
resistance
Under field condition, about 75%, 70 % and 88 % of
eggs of BPH developed into 1 st instar nymph stage, respectively
on PTB33, Udaya and TN1 generated by each
of the cohort population investigated while, hatching
percentage was higher recording 85%, 92% and 93%,
respectively under natural enemy free condition. The
trend index was low 0.72, 2.11 and 2.15 in field for
PTB33, Udaya and TN1, respectively. There was a
gradual decrease in life expectancy in the BPH populations
on all three varieties tested under natural enemy
free condition. Mortality survival ratio (MSR) was highest
for the 1 st and 2 nd instar BPH and as the insect grows,
MSR values were gradually falling and again at 5 th instar
stage there was a rise. Indispensable mortality (IM),
at egg stage was recorded maximum at early instar
stages in all the three varieties examined and was the
minimum during late instars and adult stages. Under
field condition, the mortality factors during early growth
stages included mainly mesovellid bugs, spiders and
unknown factors (environmental and host plant) but
in later stages it largely included a wide array of spiders
(viz., Lycosa sp., Marpissa sp., Cheiracanthium sp.,
Paradosa sp., Oxyopes sp., Neoscona sp. and Tetragnatha
sp.).
Virulence studies of BPH continuously reared for
15 generations on selected rice varieties viz., PTB33,
IR64, Udaya, Ramaboita and TN1 indicated that biology
of BPH in 0 th , 5 th , 10 th and 12 th generation on that
particular variety when compared to 0 th generation, a
slight variation in survival percentage and developmental
period was noticed in 10 th and 12 th generation
insects reared continuously on resistant varieties.
Role of micronutrients and microbes in
inducing resistance against rice BPH
Eight treatments viz., rice bran, Azospirillum,
Pseudomonas fluroscens, Calcium silicate, Azospirillum +
Phosphobacteria, Ferrous sulphate, Salicylic acid along
with control were tested in the net house to study their
effect on BPH resistance. Three rice cultivars namely
TN1, Udaya and Ramaboita were used for this purpose
and nymphal survival of BPH was studied.
Among the different treatments application of silica
resulted in nymphal survival of 50%, 73% and 60%,
respectively on TN1, Udaya and Ramaboita. In the control
it was 76%, 66% and 65%, respectively on TN1,
Udaya and Ramaboita indicating that mortality was
more on the susceptible check TN1.
Quantitative and Qualitative Disease
Severity Assessment
Survey for the incidence of major rice diseases
and pests in Assam and other North East
Region
The survey on occurrence of major rice diseases and
insect pests was undertaken in Baksa, Kamrup, Nalbari,
Barpeta, Darrang, Sonitpur districts of Assam and Ri
Bhoi district of Meghalaya during wet season, 2011 at
different stages of crop growth. In all the districts surveyed,
variety Ranjit & Baisamuthi was the popular
varieties grown, besides several other varieties like
Swarna Mahsuri, Mahsuri (Aijung), Bahadur, Mong
Bardhan, Barni, Kola joha and Tengre. Among the diseases
brown spot (up to disease scale of 7), bacterial
leaf blight and sheath blight (at disease scale 5) were
commonly observed, besides neck blast, bacterial streak
and sheath rot. Among the insect pests stem borer and
leaf folders were commonly prevalent in all the districts
while, hispa was also recorded from Baksa district.
At the research station, Gerua brown spot at disease
scale 7 and sheath blight at disease scale 5 were
found to be common followed by sheath rot, bacterial
leaf blight, and false smut. Important insect pests were
leaf folder and stem borer at moderate damage scale
followed by rice hispa and gundhi bug.
Analysis of Population of Dynamics of
Blast, Brown Spot and BLB
Development of monogenic differentials and
characterization of P. grisea populations
Forty one monoconidial isolates M. oryzae of Eastern
India prepared from 240 samples collected from
several districts of Assam, Arunachal Pradesh,
Jharkhand, Odisha, Meghalaya and Tripura over a period
of three years (2009-11) was pathotyped on 26 monogenic
differentials to determine their composition and
virulence structure of the population and identification
of broad spectrum resistance genes and their combination
as decision making tool for resistance breeding.
Virulence ranged from 23% (Mo-ei-205, 6 genes
defeated) to 85% (MO-ei-5, 22 genes defeated). Pi9 and
Pi ta2 were infected by the least number of isolates, the
most virulent isolate being one of them. A combination
CRRI ANNUAL REPORT 2011-12
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