PhD

Bacterial blight disease caused by Xanthomonas oryzae pv. oryzae
Ishiyama is a major constraint limiting rice production in Kerala especially
in Kuttanad, the rice bowl of Kerala. Keeping in view the limited success
achieved in controlling the disease with conventional chemicals, the
present investigation entitled "Genetic analysis of bacterial blight
(Xanthomonas oryzae pv. oryzae Ishiyama) resistance and yield in rice
(Oryza sativa L.)" was carried out at Rice Research Station, Moncompu
for the genetic analysis of bacterial blight resistance and yield in rice
for developing high yielding disease resistant varieties through the
estimation of genetic variability in a collection of germplasm, screening
and identification of resistant donors, estimation of combining ability
and gene action by line x tester analysis and the estimation of the gene
action involved in the inheritance of bacterial blight resistance and yield
by generation mean analysis.
One hundred and fifty genotypes collected from various sources
VIZ., International Rice Research Institute, Philippines, Directorate of
Rice Research, Hyderabad, different Rice Research Stations of Kerala
Agricultural University and local varieties of rice cultivated in Kuttanad,
Palakkad and Wyanad were evaluated in the field adopting a randomised
block design with two replications at Rice Research Station, Moncompu


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in additional crop of 1998. Simultaneously 150 genotypes were evaluated
in pots in CRD with 2 replications for artificial screening of bacterial
blight by clip inoculation technique.
Analysis of variance of the data revealed highly significant
difference for all the 12 characters viz; days to 50 per cent flowering,
plant height, total number of tillers hirl", number of productive tillers
hill-I, flag leaf area, 1000 grain weight, length of panicle, number of fully
filled grains panicle-I, grain yield plant! , straw yield plant", incidence
ot bacterial b\\gnt uisease a1\u sheath b\\%\\t \l\c\uem:e \l\U\c:a.\\ws \\\~
presence of high variability. The pathogen was identified as Pathotype I
based on the resistant reaction on DV 85 and susceptible reaction on IR8,
IR20, Kogyoku, Malagkit Sung song and Rantai Emas. All the characters
except total number of tillers hill-1 and flag leaf area recorded high
estimates of GCV indicating the presence of greater genetic variability
and better scope for the genetic improvement of these characters by
means of selection.
High heritability estimates along with moderate to high GA
recorded for days to 50 per cent flowering, number of productive tillers
hill-I, length of panicle, grain yield plane 1 and percentage of bacterial
blight disease incidence suggests that the above characters are under the
control of additive gene action. Therefore, the above characters may be
considered during selection programme for the improvement of yield and
bacterial blight resistance.
Six high yielding locally adapted varieties and three bacterial blight
resistant donors were selected from the evaluation of germplasm

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(Experiment 1) and crossed in a Line x tester fashion during Puncha 98-
99 at Rice Research Station, Moncompu and 18 LxT combinations were
developed. The six lines, 3 testers and 18 LxT combinations were
evaluated in an RBD with 3 replications during the additional crop season
of 1999. Data on eleven traits collected from field experiment were
subjected to L x T analysis for estimating combining ability.
Simultaneously the six selected lines, 3 testers and their 18 LxT
combinations were raised in pots in CRD with 3 replications for artificial
inoculation and screening of BB and percentage incidence of BB was
recorded based on standard evaluation system for rice (IRRI, 1980) and
subjected to statistical analysis.
Analysis of variance revealed significant difference among parents
and crosses. On further analysis there was significant difference among
lines also. Based on the mean performance and gca effects for grain
yield and yield attributing characters Uma and Aruna among the lines were
the best genotypes. With regard to 50 per cent flowering, plant height
etc. Jyothy among the lines was found to be the best. For bacterial blight
resistance, the testers viz., BJ1 and DV 85 were found to be the best
genotypes. Based on the mean performance and sea effects, the crosses
Aruna x BJ 1, Uma x DV 85 and Jyothy x DV 85 were identified as the
best specific combiners. These hybrids showed negative sca effect with
respect to days to 50 per cent flowering, plant height and percentage of
bacterial blight disease, where as positive sca effect was recorded for
almost all the yield and yield attributing characters. Hence the above
three cross combinations may be carried forward by pedigree selection






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for identifying and selecting desirable recombinants with high yield along
with bacterial blight resistance.
The three superior crosses identified from the evaluation of Line
x tester crosses were utilized for generation mean analysis. The three
selected F 1 S and their respective parents were planted in a crossing block
during Puncha 99-2000 at Rice Research Station, Moncompu. Six
generations PI' P 2' F l' F 2' Bland B2 developed in the three selected cross
combinations were evaluated in an RBD with 3 replications during the
additional crop season of 2000 at Rice Research Station, Moncompu. All
the six generations of 3 crosses were raised in pots for artificial
inoculation and screening against bacterial blight disease incidence. From
generation mean analysis of six generations, the additive, dominance and
epistatic gene actions were estimated for 11 traits.
In all the three crosses, significance of scaling tests revealed the
presence of non allelic interaction for the ten characters studied. None
of the scales was significant for the number of productive tillers hill-1 in
Aruna x BJI and Jyothy x DV 85 indicating the absence of epistasis. In
Uma x DV 85 significance of scale D indicates additive x additive (i)
type of gene action.
For plant height only the additive effect (d) was found to be
negative and significant in all the three crosses indicating the posibility
of developing dwarf types by simple selection.
The magnitude of dominance (h) and additive x additive (i) type
of interaction were greater than other types of gene action for most of

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the yield components in all the three crosses and hence recurrent
selection is suggested for the improvement.
For percentage of bacterial blight disease incidence the magnitude
of dominance and dominance x dominance (1) interaction was greater than
additive gene action for all the 3 crosses. Hence combination breeding
is advocated for the improvement.
Utilizing the genetic components, magnitude of heterosis were
estimated for eleven characters in all the th~ee crosses. Days to 50 per
cent flowering and percentage of bacterial blight disease incidence
registered a significant negative heterotic effect for all the three crosses
suggesting the possibility of developing early flowering and disease
tolerant varieties. In Uma x DV 85, flag leaf area and number of fully
filled grains panicle"! recorded significant positive heterotic effect which
can be utilized for developing high yielding varieties.
Estimates' of transgressive segregants In F 2 for 11 characters
revealed transgressive segregation on both directions in all crosses
indicating the possibility of identifying desirable recombinants which can
be further utilized for developing superior varieties.
It can be concluded that three superior crosses viz., Aruna x ,BJ 1,
Uma x DV 85 and Jyothy x DV 85 identified in this study may be carried
forward by pedigree method for developing high yielding, bacterial blight
disease resistant varieties.