Characterization and management of viral diseases of black pepper(Piper nigrum L.)

Abstract

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.