MSc

Cowpea, Vigna unguiculata (L.), is an important legume of the tropics and
subtropics. It is used as a grain, vegetable and fodder crop. Cowpea is cultivated
as a vegetable crop across an area of 6714 ha in Kerala (DES, 2014). However,
the productivity of cowpea, at 625 kg ha-1 is very low, one of the reasons being
infestation by insect pests. Among the different insect pests, the legume pod
borer, Maruca vitrata (Fab.) is the most important one causing loss of up to 60 per
cent in cowpea (Singh and van Emden, 1979).
The larvae of the spotted pod borer, as the name implies, bore into buds,
flowers and pods and feed on internal tissues. Their concealed nature protects the
larvae from natural enemies as well as application of insecticides to a considerable
extent, making management of the pest difficult. Exploitation of host plant
resistance, which is one of the most effective and eco friendly pest management
strategies, has hardly been attempted in case of cowpea.
It was in this context that the present study „Morphological and
biochemical bases of resistance to spotted pod borer, Maruca vitrata (Fab.)
(Lepidoptera: Crambidae) in cowpea’ was undertaken in the Department of
Agricultural Entomology, College of Horticulture, Kerala Agricultural University,
Thrissur during 2014 - 2015. The objectives of the experiment were to evaluate
degree of resistance to pod borer in selected accessions of cowpea, as well as to
identify the morphological and biochemical bases of resistance in cowpea to pod
borer.
Forty eight accessions, obtained from different sources, were evaluated for
resistance to the spotted pod borer, M. vitrata. Significant variation was observed
between the genotypes to pod borer damage at bud, flower and pod stages.
The extent of borer infestation varied from zero to 41.04 per cent. Five
accessions, viz., EC 100092, IC 39945, IC 2918, EC 98668 and IC 52110
recorded zero per cent damage at all the three stages. Twenty - six accessions
recorded damage varying from 0.1 to 9.29 per cent and were on par with each
other. All the above accessions were rated as resistant.
Seventeen accessions with borer damage ranging from 11.15 to 41.04 per
cent were rated as susceptible. The variety Bhagyalakshmy recorded the highest
damage of 32.5, 50.39 and 47.95 per cent for bud, flower and pod respectively.
Analysis of morphological basis of resistance to pod borer indicated that
pod wall thickness was significantly and negatively correlated with per cent
damage. Similarly trichome density was also negatively correlated with pod
damage, though the correlation was not significant. Length of flower stalk as well
as length of trichomes was positively correlated with borer damage but the
correlation was not significant.
Significant positive correlation was observed between per cent damage
and total protein content, moisture content, total sugars and reducing sugars.
However, significant negative correlation was observed in peroxidase and
polyphenol oxidase activity with per cent damage.
The study confirmed variability among cowpea genotypes in response to
pod borer infestation, indicating the potential for utilization of host plant
resistance in the management of pod borer in cowpea. It also indicated that the
resistance in cowpea to Maruca vitrata could be related to biochemical
constituents of the plant, which, however, need to be confirmed.