PhD

The present investigation was undertaken to correctly
identify the species of Phytophthora causing bud rot of coconut
and foot rot of pepper in Kerala and to find out their
comparative role in causing diseases on coconut and pepper. The
study also aimed at isolation of viable antagonistic agents
against the pathogen, so as to utilize them in future for
biological control.
The study was conducted during 1992-96 at College of
Agriculture, Vellayani and Indian Institute of Spices Research,
Kozhikode. Detailed symptomatology of both the diseases at
different locations were studied. Periodic collections were made
from diseased coconut and pepper from seven districts of Kerala.
The morphological characters of the isolates were
studied in detail. The length, breadth, L/B ratio, pedicel
length and caducity of sporangia of coconut isolates were smaller
than pepper isolates. The sporangial shapes differed
considerably between and among the isolates. All the isolates
except those collected from Kannur and Kasaragod districts
(C7 - C16), produced abundant number of sporangia on carrot agar.
Phytophthora are either heterothallic or homothallic.
Generally P. palmivora and P. capsici are heterothallic. But ten

coconut isolates obtained from Kannur and Kasaragodu districts
produced abundant number of sexual structures on carrot agar,
indicating their homothallic nature and this is the first report
of homothallic Phytophthora causing bud rot of coconut in Kerala.
All other 52 isolates were mated with known A1 and A2 mating type
and all the coconut isolates produced oospores with A1 and all
the pepper isolates produced oospores when mated with A2.
Zoospore production was induced from sporangia using
cold treatment. The number of zoospores in sporangia ranged from
6-15 in number. Chlamydlospore production was a rare phenomenon
in pepper isolates while all the coconut isolates and five pepper
isolates produced chlamydospores.
All the isolates were inoculated into pepper seedlings,
coconut leaves, tender coconut and coconut seedlings and the time
required for infection, variation in symptom expression by
different isolates etc. were studied. All the sixteen coconut
isolates produced foot rot in pepper. Fourty six isolates of
pepper produced lesions on coconut leaves and nut rot in tender
coconut, while, only six isolates of pepper produced bud rot in
coconut plants. The cross infectivity of pepper isolates needed
further confirmation to prove the point beyond doubt. Eight
cultivated plants, 9 ornamental plants and 12 weed plants were
tested for the host range of coconut and pepper isolates. Many
plants belonged to the above three groups took infection
successfully.

The microorganisms found associated with healthy and
diseased pepper and coconut plantations and microorganisms from
soils of pepper and coconut gardens of different parts of Kerala
were isolated. Out of more than 200 microorganisms, only 28
fungi inhibited the growth of Phytophthora in vitro. On pepper
plant, 12 isolates had inhibitory action. Three organisms, viz.,
Verticillium chlamydosporium, Aspergillus terreus and Chaetomium
sp checked the pathogen completely even after seven days of
spraying with the organisms.