Anju Viswanathan, K
Characterisation of resistance in Okra (ABELMOSCHUS ESCULENTUS L.(MOENCH)) aganist shoot and fruit borer.,Earias vitella Fab. (Lepidoptera :Noctuidae) - Vellanikkara Department of Agricultural Entomology, College of Agriculture 2024 - 144,xixp.
Ph.D
Okra, also known as ladies finger, is one of the most extensively cultivated
vegetable crops in the world. India ranks first in the world in okra cultivation with
an annual production of 6466 thousand MT across an area of 531 thousand hectares
with a productivity of 12.0 MT/ha. Yet, the crop suffers yield loss to the tune of 35
to 40 per cent due to biotic stresses alone. The okra shoot and fruit borer, Earias
vitella is one of the most destructive insect pests of okra, often accounting for 35 to
80 per cent yield loss. The borer is managed mostly through chemical means, which
leads to issues such as residues in fruits and adverse environmental effects. In this
backdrop, more benign options against E. vitella like the use of host plant resistance
assume great significance, as use of resistant varieties constitute one of the safest
and cost-effective methods of pest management.
It was in this context that the present study “characterisation of resistance in
okra (Abelmoschus esculentus L. (Moench)) against shoot and fruit borer, Earias
vitella Fab. (Lepidoptera: Noctuidae)” was undertaken at the Department of
Agricultural Entomology, College of Agriculture, Vellanikkara, Kerala Agricultural
University, Thrissur, during 2020 to 2023. Exploitation of plant resistance calls for
screening of existing germplasm for sources of resistance, understanding the
mechanisms of resistance and the factors that influence expression of plant
resistance. The study aimed to throw light into these dimensions of resistance in
okra to E. vitella.
Fifty genotypes of okra, collected from different sources, were screened for
resistance to shoot and fruit borer, E. vitella under open field conditions. Significant
variation was observed between the genotypes in terms of shoot and fruit damage.
Shoot damage varied from 0 to 30 per cent. Susthira, the okra variety released from
KAU had recorded zero shoot damage and was followed by the genotype IC 140906
with 9.79 per cent mean shoot damage. The NBPGR accessions IC 128076 and IC
43748 recorded highest mean shoot damage of 28.21 and 30.0 per cent respectively.
The fruit damage ranged from 3.42 in Susthira to 85.31 per cent in IC 117123.
Susthira was rated as highly resistant, while IC 282294 and Aruna, with mean fruit
damage of 11.53 and 20.14 per cent respectively, were rated as moderately resistant.
IC 218900, IC 140906 and IC 128885 with mean fruit damage between 21-30.99 per
cent were classified as susceptible and rest of the genotypes, with more than 31 per
cent fruit damage were assessed as highly susceptible.
Biophysical characteristics such as trichome length, trichome density, fruit
length, fruit width, fruit rind thickness, fruit colour and shoot diameter were also
recorded for all the fifty genotypes along with shoot and fruit damage. It was
observed that trichome density, fruit length, and fruit rind thickness had significant
negative correlation with fruit damage, while trichome length and fruit width
enjoyed a positive correlation. Shoots of the resistant variety Susthira possessed
modified secretory parenchyma for enhanced production of mucilage and defence
compounds, thicker collenchyma for mechanical strength and also a thicker cortex,
when compared to susceptible accessions.
Significant positive correlation was also observed between fruit damage and
biochemical parameters such as moisture content, total sugar, reducing sugar and
protein. However, significant negative correlation existed between fruit damage and
phenol, fibre and gossypol contents.
Studies on the feeding preference of third instar larvae of E. vitella to
selected okra genoytypes, through multi-choice test revealed that Susthira attracted
the lowest mean value of 0.08 per cent out of the 25 larvae released. The moderately
resistant IC 282284 and Aruna had 9.60 and 11.20 per cent larvae feeding on them
24 h after release, while the highly susceptible genotypes, between them, attracted
78.40 per cent of the larvae released. Similarly, in a free-choice test using the seven
selected genotypes of okra to assess the ovipositional preference of adult E. vitella
moths, the highest mean number of 117.91 eggs were laid on plants of IC 128076,
followed by IC 282266, IC 282284 and IC 117123, with 117.90, 114.00 and 109.88
eggs/ plant respectively, all of which were categorized as highly susceptible
genotypes to shoot and fruit borer in the present study. Significantly lower number
of eggs were laid on the highly resistant Susthira (21.13 eggs/ plant) as well as the
moderately resistant IC 282294 (59.26 eggs/ plant), and Aruna (65.89 eggs/ plant).
Considerable variation was observed in the embryonic and post-embryonic
development of E. vitella when reared on different okra genotypes under no-choice
conditions. E. vitella recorded the shortest mean incubation period of 2.60 days, the
lowest mean larval duration of 5.60 days, the longest mean pupal period of 11.05
days and the shortest mean adult longevity of 7.10 days when reared on Susthira.
The insect also registered the lowest larval and pupal weight of 0.0638 and 0.0471 g
respectively on Susthira, suggesting an antibiotic mechanism of resistance. On the
contrary, E. vitella recorded the longest egg incubation period, of 4.30 days, the
longest larval duration of 13.20 days, the shortest pupal duration of 6.15 days and
the longest adult longevity of 15.90 days on the highly susceptible genotype IC
117123. The GC-HRMS and HR-LCMS analyses of the resistant Susthira revealed
the presence of several insect repellents, feeding and oviposition deterrents, growthregulating compounds and insecticidal compounds in the hexane and methanol
fractions of Susthira.
The impact of spacing and fertilizer regimes on expression of plant
resistance in okra against shoot and fruit borer was studied by planting Susthira in a
3x3 factorial design. The three levels of spacing were S1 (65 cm x 50 cm); S2 (60
cm x 45 cm) and S3 (55 cm x 40 cm) while the three levels of fertilizers were N1
(138: 44: 88 kg of NPK haˉ¹), N2 (110: 35: 70 kg of NPK haˉ¹) and N3 (83: 27: 53
kg of NPK haˉ¹). There was no shoot damage to Susthira in any of the treatment
combinations. The mean fruit damage varied significantly among the different
treatments. The highest fruit damage of 3.02 per cent was observed in S1N1, which
was followed by S2N1 (2.60%) and S2N2 (2.31%). The lowest damage of 0.57%
was recorded in S3N3, which was significantly lower than that of other treatments.
The study brought out the variability in the response of different okra
genotypes to shoot and fruit borer infestation, indicating the potential for utilization
of host plant resistance in the management of shoot and fruit borer in okra. The
resistance has been shown to be based on the morphological and biochemical
attributes of plant, which, however, need to be confirmed. Both antixenosis and
antibiosis mechanisms could be involved in the resistance of okra genotypes to E.
vitella. The highly resistant Susthira recorded zero shoot damage and very low fruit
damage under different agronomic regimes, suggesting a very strong and stable
resistance in this genotype.
Agricultural entemology
ABELMOSCHUS ESCULENTUS L.
Resistance in Okra
632.6 / ANJ/CH Ph.D
Characterisation of resistance in Okra (ABELMOSCHUS ESCULENTUS L.(MOENCH)) aganist shoot and fruit borer.,Earias vitella Fab. (Lepidoptera :Noctuidae) - Vellanikkara Department of Agricultural Entomology, College of Agriculture 2024 - 144,xixp.
Ph.D
Okra, also known as ladies finger, is one of the most extensively cultivated
vegetable crops in the world. India ranks first in the world in okra cultivation with
an annual production of 6466 thousand MT across an area of 531 thousand hectares
with a productivity of 12.0 MT/ha. Yet, the crop suffers yield loss to the tune of 35
to 40 per cent due to biotic stresses alone. The okra shoot and fruit borer, Earias
vitella is one of the most destructive insect pests of okra, often accounting for 35 to
80 per cent yield loss. The borer is managed mostly through chemical means, which
leads to issues such as residues in fruits and adverse environmental effects. In this
backdrop, more benign options against E. vitella like the use of host plant resistance
assume great significance, as use of resistant varieties constitute one of the safest
and cost-effective methods of pest management.
It was in this context that the present study “characterisation of resistance in
okra (Abelmoschus esculentus L. (Moench)) against shoot and fruit borer, Earias
vitella Fab. (Lepidoptera: Noctuidae)” was undertaken at the Department of
Agricultural Entomology, College of Agriculture, Vellanikkara, Kerala Agricultural
University, Thrissur, during 2020 to 2023. Exploitation of plant resistance calls for
screening of existing germplasm for sources of resistance, understanding the
mechanisms of resistance and the factors that influence expression of plant
resistance. The study aimed to throw light into these dimensions of resistance in
okra to E. vitella.
Fifty genotypes of okra, collected from different sources, were screened for
resistance to shoot and fruit borer, E. vitella under open field conditions. Significant
variation was observed between the genotypes in terms of shoot and fruit damage.
Shoot damage varied from 0 to 30 per cent. Susthira, the okra variety released from
KAU had recorded zero shoot damage and was followed by the genotype IC 140906
with 9.79 per cent mean shoot damage. The NBPGR accessions IC 128076 and IC
43748 recorded highest mean shoot damage of 28.21 and 30.0 per cent respectively.
The fruit damage ranged from 3.42 in Susthira to 85.31 per cent in IC 117123.
Susthira was rated as highly resistant, while IC 282294 and Aruna, with mean fruit
damage of 11.53 and 20.14 per cent respectively, were rated as moderately resistant.
IC 218900, IC 140906 and IC 128885 with mean fruit damage between 21-30.99 per
cent were classified as susceptible and rest of the genotypes, with more than 31 per
cent fruit damage were assessed as highly susceptible.
Biophysical characteristics such as trichome length, trichome density, fruit
length, fruit width, fruit rind thickness, fruit colour and shoot diameter were also
recorded for all the fifty genotypes along with shoot and fruit damage. It was
observed that trichome density, fruit length, and fruit rind thickness had significant
negative correlation with fruit damage, while trichome length and fruit width
enjoyed a positive correlation. Shoots of the resistant variety Susthira possessed
modified secretory parenchyma for enhanced production of mucilage and defence
compounds, thicker collenchyma for mechanical strength and also a thicker cortex,
when compared to susceptible accessions.
Significant positive correlation was also observed between fruit damage and
biochemical parameters such as moisture content, total sugar, reducing sugar and
protein. However, significant negative correlation existed between fruit damage and
phenol, fibre and gossypol contents.
Studies on the feeding preference of third instar larvae of E. vitella to
selected okra genoytypes, through multi-choice test revealed that Susthira attracted
the lowest mean value of 0.08 per cent out of the 25 larvae released. The moderately
resistant IC 282284 and Aruna had 9.60 and 11.20 per cent larvae feeding on them
24 h after release, while the highly susceptible genotypes, between them, attracted
78.40 per cent of the larvae released. Similarly, in a free-choice test using the seven
selected genotypes of okra to assess the ovipositional preference of adult E. vitella
moths, the highest mean number of 117.91 eggs were laid on plants of IC 128076,
followed by IC 282266, IC 282284 and IC 117123, with 117.90, 114.00 and 109.88
eggs/ plant respectively, all of which were categorized as highly susceptible
genotypes to shoot and fruit borer in the present study. Significantly lower number
of eggs were laid on the highly resistant Susthira (21.13 eggs/ plant) as well as the
moderately resistant IC 282294 (59.26 eggs/ plant), and Aruna (65.89 eggs/ plant).
Considerable variation was observed in the embryonic and post-embryonic
development of E. vitella when reared on different okra genotypes under no-choice
conditions. E. vitella recorded the shortest mean incubation period of 2.60 days, the
lowest mean larval duration of 5.60 days, the longest mean pupal period of 11.05
days and the shortest mean adult longevity of 7.10 days when reared on Susthira.
The insect also registered the lowest larval and pupal weight of 0.0638 and 0.0471 g
respectively on Susthira, suggesting an antibiotic mechanism of resistance. On the
contrary, E. vitella recorded the longest egg incubation period, of 4.30 days, the
longest larval duration of 13.20 days, the shortest pupal duration of 6.15 days and
the longest adult longevity of 15.90 days on the highly susceptible genotype IC
117123. The GC-HRMS and HR-LCMS analyses of the resistant Susthira revealed
the presence of several insect repellents, feeding and oviposition deterrents, growthregulating compounds and insecticidal compounds in the hexane and methanol
fractions of Susthira.
The impact of spacing and fertilizer regimes on expression of plant
resistance in okra against shoot and fruit borer was studied by planting Susthira in a
3x3 factorial design. The three levels of spacing were S1 (65 cm x 50 cm); S2 (60
cm x 45 cm) and S3 (55 cm x 40 cm) while the three levels of fertilizers were N1
(138: 44: 88 kg of NPK haˉ¹), N2 (110: 35: 70 kg of NPK haˉ¹) and N3 (83: 27: 53
kg of NPK haˉ¹). There was no shoot damage to Susthira in any of the treatment
combinations. The mean fruit damage varied significantly among the different
treatments. The highest fruit damage of 3.02 per cent was observed in S1N1, which
was followed by S2N1 (2.60%) and S2N2 (2.31%). The lowest damage of 0.57%
was recorded in S3N3, which was significantly lower than that of other treatments.
The study brought out the variability in the response of different okra
genotypes to shoot and fruit borer infestation, indicating the potential for utilization
of host plant resistance in the management of shoot and fruit borer in okra. The
resistance has been shown to be based on the morphological and biochemical
attributes of plant, which, however, need to be confirmed. Both antixenosis and
antibiosis mechanisms could be involved in the resistance of okra genotypes to E.
vitella. The highly resistant Susthira recorded zero shoot damage and very low fruit
damage under different agronomic regimes, suggesting a very strong and stable
resistance in this genotype.
Agricultural entemology
ABELMOSCHUS ESCULENTUS L.
Resistance in Okra
632.6 / ANJ/CH Ph.D