PhD

The spotted pod borer, Maruca vitrata Fab. (Lepidoptera: Crambidae) is a major
constraint in the production of legumes because of its wide host range, distribution and
destructiveness. In cowpea, the loss due to pod borer infestation varies from 20 to 60 per
cent, often reaching upto 80 per cent in severe cases. Application of pesticides can hardly
be recommended in cowpea as the pods are harvested at alternate days.
Biological control of M. vitrata using entomopathogenic microorganisms has
received considerable attention in recent times. Previous studies have demonstrated the
potential of entomopathogenic organisms to colonise an array of plants and confer
protection from insect pests. In this context, a study entitled “Endophytic fungi for the
management of spotted pod borer, Maruca vitrata Fab. (Lepidoptera: Crambidae) in
cowpea” was undertaken with an objective of isolation and characterization of endophytic
entomopathogenic fungi in cowpea, standardization of method of inoculation of
entomopathogenic fungi in cowpea, and evaluation of selected endophytic fungi for
management of the spotted pod borer, M. vitrata.
Purposive sampling surveys were conducted in the major cowpea growing areas of
Kozhikode, Thrissur, Kottayam and Thiruvananthapuram districts of Kerala. A total of 235
endophytic fungal isolates were obtained from the cowpea plant samples collected from 40
locations. This comprised of 103 isolates from roots, 63 from stems, 31 from leaves, 33
from pods and five from flowers. Nine accessions of cowpea with different levels of
resistance were also screened for the isolation of fungal endophytes. All the accessions
were found to harbor endophytic fungi and yielded 32 isolates. Among these accessions,
Palakkadan thandan payar yielded the maximum number of seven endophytic fungi. Lola
and Mysore local had the lowest number of isolates. In contrast to the results of survey, the
leaves of cowpea plant harbored more endophytic fungi than other plant parts. A total of
267 isolates were obtained from survey samples and cowpea accessions. Three isolates
were found to be pathogenic to M. vitrata. They were identified as Fusarium oxysporum
(EEF 1) and two isolates of Purpureocillium lilacinum (EEF 4 and EEF 64) through
morphological and molecular characterization. These isolates were evaluated along with
Beauveria bassiana (NBAIR strain) for their bioefficacy against M. vitrata.
The best two organisms in the bioefficacy studies, viz., B. bassiana (NBAIR strain)
and P. lilacinum (EEF 4) were used for standardizing the inoculation technique for
endophytic colonization in cowpea plant. Three different methods of inoculation viz., seed,
soil and foliar inoculation were evaluated for identifying the best method for colonization
of entomopathogenic fungi in cowpea plants. The effect of fungal colonization on
infestation of spotted pod borer in cowpea was further assessed under field condition.
Foliar inoculation with B. bassiana registered the lowest mean pod damage of 12.53
per cent. B. bassiana applied as foliar application resulted in the highest marketable pod
yield of 152.83g plant-1
, followed by P. lilacinum as foliar application (149.33g plant-1
).
Based on the polyhouse and field studies, it was inferred that foliar application of B.
bassiana was found to be the best treatment against the target pest, M. vitrata. In addition,
the results of the current study suggested that that endophytic colonization in cowpea had
little adverse impact on plant growth and yield.
Foliar application of B. bassiana, which was identified as the most effective
treatment against pod borer in the previous studies, was selected for comparative evaluation
with the diamide insecticide, flubendiamide against M. vitrata. Cowpea plants treated with
both flubendiamide and B. bassiana had significantly less number of infested pods than
control, with 8.41 and 15.05 per cent infestation respectively. Control plants recorded the
highest infestation of 21.28 per cent. Mean marketable pod yield showed significant
difference between flubendiamide (166.14g plant-1
) and foliar inoculation of B. bassiana
(155.14g plant-1
). Both these treatments also had significantly higher marketable pod yield
compared to control plants (139.29g plant-1
).
In conclusion, the present study revealed that use of B. bassiana as an endophyte
could be a useful tool in integrated pest management of pod borer in cowpea. However,
further studies are needed to understand the mechanisms through which the endophytes
protect plants from herbivores and promote plant growth and yield.