PhD

A detailed survey was undertaken to study the occurrence and
distribution of viral diseases in black pepper in Thiruvananthapuram and
Kollam districts of Kerala. Disease incidence (DI) and per cent disease
index (PDI) were determined during survey which showed that per cent DI
varied between 0-57 and PDI between 0-18. The disease was prevalent in
both the districts. Most of the local cultivars and improved varieties were
susceptible to the disease. The characteristics symptoms of disease were
chlorotic spots on emerging younger leaves, vein clearing, scattered
chlorotic flecks followed by chlorotic mottling along veins leading to
interveinal chlorosis and characteristic twisting and curling of leaves. The
infected leaves were also observed to be small, crinkled, and brittle with
reduced internodal length, leading to typical stunting of plants. Most of
the diseased plants were found to be infected with both Cucumber mosaic
virus (CMV) and Pepper yellow mottle virus (PYMo V). The presence of
these viruses was confirmed through conducting enzyme linked
immunosorbent assay (ELISA) on representative samples collected from
different locations. The virus was not mechanically transmitted to healthy
pepper seedlings. However the virus was found to be transmitted through
grafting, insect vectors and also through seeds. The mealy bug, Ferrisia
I
virgata was found to be the efficient vector although aphid, Toxoptera
aurantii, was also found to be transmitting the virus. Thermal inactivation
point was recorded at a range of 40-450C and dilution end point between
10-3 and 10-4 for CMV. Host range studies revealed that virus could be
readily transmitted to other species in Piperaceae family as well to some
of the weed hosts. The virus was partially purified and antiserum was
produced with a titre of 1:128. Identification and serological
characterization of the virus was done using ELISA and DIBA. Molecular
detection of the virus was also performed using PCR and a PCR product of
amplicon size 500 bp and 300 bp were obtained for primers specific to




CMV and banana streak virus (BSV) respectively. The pathophysiological
studies revealed that virus infected plants showed increased phenol,
carbohydrate and protein content. The chlorophyll content was found to be
less in infected samples. The activity of defence related enzymes like
peroxidase, polyphenol oxidase and phenylalanine ammonialyase were
found to be more in infected plants. Electrophoretic analysis of virus
infected samples through SOS-PAGE revealed the presence of two novel
proteins in diseased samples. Analysis of isozymes through native gel
revealed the production of an additional isoform of peroxidase and over
expression of polyphenol oxidase in infected plants. In screening of
varieties for the source of resistance Panniyur, 2, 3 and 4 were found
moderately resistant and Karimunda was highly susceptible. Piper
colubrinum showed resistance to the virus. Meristem culure attempted was
unsuccessful and could not be used as a viable strategy for eliminating the
virus infecting black pepper as the meristems were seen contaminated with
the pepper badnavirus.