PhD

"Management of pumpkin mosaic using selected medicinal plant extracts"
was undertaken in the College of Horticulture, Kerala Agricultural University,
Vellanikkara, Thrissur during 1998-2002. Selection of suitable medicinal plant
having antiviral property to pumpkin mosaic virus (PMV), isolation of the
inhibitory principle present in the medicinal plant, management of pumpkin mosaic
using the plant extract and partial purification and serological studies of PMV were
the objectives of the study. Symptomatology, transmission, host range and
electron microscopy of PM V were also studied.
The symptomatology of pumpkin mosaic was studied by observing the
development of symptoms in naturally infected as well as artificially inoculated
pumpkin plants. The symptoms appeared as typical mosaic mottling with light and
dark green patches in the leaf lamina. This was followed by blistering and
malformation of leaves into filiform or some other shapes and resulted in reduction
of leaf area. The infected plants were stunted, flowered very sparingly with less
number of female flowers and reduced fruit setting. The fruits were often
malformed . The virus could be transmitted mainly through sap and vector, Aphis
gossypii. The virus found to be weakly transmitted also through seeds. The
inoculation of PMV on host plants of four families viz., cucurbitaceae, solanaceae,
fabaceae and caricaceae showed systemic infection in water melon, snake gourd,
bitter gourd, winter squash,' wild ash gourd (cucurbitaceae) chilli, datura
(solanaceae), soybean, cow pea (fabaceae) and papaya (caricaceae). Electron
microscopic studies revealed the presence of flexuous virus particles (700-800 x 11
nm) in infected leaf sample.
Antiserum was raised against the virus and used for serodiagnostic work.
The antiserum showed serological relationship with poty viruses infecting snake
gourd, bitter gourd, wild ash gourd, cowpea, soybean, chilli and papaya. DAC-
ELISA procedure was standardized and used for detection of PM V from pumpkin.

The inhibitory property of extracts of five medicinal plants namely Basella
alba, Glycyrrhiza glabra, Phyllanthus fraternus, Plumbago rosea 'and Thespesia
populnea were studied-against PMV by pre-inoculation application on pumpkin
seedlings. The medicinal plant extracts were prepared using different extraction
media viz., chloroform, distilled water, ethyl acetate and petroleum ether at
different dilutions. The inhibitory property varied with extraction media and
dilution used.
The PMV inhibitory property of different parts of Plumbago viz., tender
leaf, mature leaf, tender stem, mature stem and root were studied at different
temperatures and found that all parts showed inhibitory property which varied with
temperature. The root extract which showed the maximum inhibitory property at
30°C (near to room temperature) was used for further studies.
The effect of Plumbago on vector transmission was studied by applying
the extract before acquisition feeding and inoculation feeding of Aphis gossypii,
the vector of PMV. Application before inoculation feeding was found to be
effective than acquisition feeding and the inhibitory effect decreased with time
after application.
Distilled water extract of Plumbago was separated through silica gel
column to isolate the inhibitory fraction and found that individual fractions were
not effective as plant extract as such against PMV.
The inhibitory effect of Plumbago water extract one per cent, on artificially
inoculated and healthy pumpkin seedlings was tested by weekly, fortnightly,
monthly, bimonthly and single application. Weekly spray was effective to reduce
disease severity of artificially inoculated and naturally infected pumpkin seedlings.
Delayed incidence of the mosaic and enhanced yield of infected plants was also
resulted due to weekly spray of the extract.
Enzyme, protein, chlorophyll and phenolics estimation revealed that
Plumbago extract spray favoured the resistance and thereby suppression of
symptoms. The DAC-ELISA of field samples showed the lower concentration of
the virus in Plumbago treated plants.