MSc

An investigation on "Parasitism of Hirsutella thompsonii Fischer var.
synnematosa Samson, McCoy & O'DonneU on coconut eriophyid mite Aceria
guerreronis (Keifer)" was carried out at the Department of Plant Pathology,
College of Horticulture, Vellanikkara. The main objectives of the study were to
explore the cultural, physiological, toxicological characters of the fungus,
compatibility of the fungus with pesticides and botanicals and mass multiplication
characteristics of the fungus, which could be used as an efficient biocontrol agent
on coconut mite. The results of this investigation revealed the following
conclusions.
From the mite infested young nuts collected from the coconut garden of
College of Horticulture, Vellanikkara, the acaropathogen H. thompsonii var.
synnematosa was isolated and its pathogenicity on mite was proved.
Sabouraud's maltose agar + yeast was selected as the most suitable solid
medium for the growth and sporulation of the fungus. Maximum number of
fruiting bodies called synnemata were produced in Richard's medium. Correlation
study revealed a significant positive correlation between mycelial growth and
sporulation. Ninety six per cent germination of spores of the fungus grown in solid
medium was recorded after eight hours of incubation.
In the different liquid media tried, Sabouraud's maltose+yeast was
selected as the best for maximum dry mycelial weight and sporulation. Only
twenty five per cent germination was recorded after eight hours of incubation of
spores of the fungus grown in liquid medium. Maximum sporulation and
germination percentage of spores of the fungus were recorded in solid media
compared to liquid media.


Microscopic observations showed that in all the solid media the hyphae
were hyaline, septate, smooth and branched producing conical to flask shaped
phialides with narrow neck. Phialides were branched often once. Spores were
spherical, verrucose and hyaline. Hyphal width, phialide width and spore diameter
,
ranged between 3.33 urn to 3.76 urn in different solid media. Maximum number of
phial ides in a unit length of hypha was in Sabouraud's maltose agar + yeast.
The fungus preferred an alkaline pH of 9. But it gave satisfactory
growth on a wide range of pH from 5 to 9. Growth of the fungus was recorded only
in temperatures of 25 and 30oe. No significant difference was recorded in the
fungal growth at humidity levels of 50 to 90 per cent.
Both exotoxin and endotoxin were extracted from the liquid culture of
the fungus. In closed perianth condition there was no significant difference in the
per cent mortality of mites due to spraying with both the toxins, but it was superior
than spraying with water (control). In open perianth condition there was no
significant difference in the percentage mortality of mites on spraying with both
the toxins and water.
The decreasing order of the inhibition of fungal growth by
insecticides/acaricides was dicofol, carbaryl, triazophos, wettable sulphur and
endosulfan. The fungicides bordeaux mixture and copper oxychloride showed cent
per cent inhibition of fungal growth whereas potassium phosphonate (akomin)
recorded minimum inhibition over control. Among the botanicals, maximum
inhibition of fungal growth was with garlic + neem oil and azadirachtin showed
least inhibition.
In the two phase mass production study, wheat was identified as the
most promising raw substrate for sporulation and germination percentage of spores
of the fungus. In the powdered substrates tried, growth was present only in loose
substrates like rice bran and tea waste.