MSc

Black pepper (Piper nigrum L.) is a perennial, woody and flowering climber
belonging to family Piperaceae. It is one of the important spice crops which provides
major source of income and employment for rural households in Kerala. Wayanad
dominated in pepper farming in the state about 20 years ago. Annual production of
pepper was 40,000 tonnes in the mid-1980s, which comprised about half of India’s
total pepper production. But recently, the production has declined drastically due to
the infestation of pests and diseases. Foot rot caused by Phytophthora capsici and
yellowing of black pepper are the major diseases devastating most of the plantations
in Wayanad. However, some of the plants in the disease affected areas remain healthy
which could be due to inherent activity of native rhizosphere microflora. The present
study focused on assessing the functional diversity of beneficial microorganisms
which could possibly be exploited for the benefit of plant growth.
Four healthy gardens, four gardens each affected by foot rot and yellowing
were selected for sample collection. Rhizosphere soil samples were collected from
five healthy vines in each garden. Population of beneficial microbes in the
rhizosphere soils of healthy and disease affected gardens were compared. In general,
rhizosphere soil from healthy gardens recorded higher population of bacteria, fungi,
phosphate solubilizers and fluorescent pseudomonads. A total of 207 isolates
(including 112 bacteria, 32 actinomycetes and 63 fungi) were purified and maintained
to study their plant growth promoting and antagonistic activities.
Maximum IAA production (292.50 μg ml-1) was recorded by HPLBC-6
followed by HABC-3 (46.43 μg ml-1). The isolate HPLPSB-3 was the most efficient
P solubiliser (162.7 μg ml-1) followed by HPLF-5 (161.3 μg ml-1). The isolate YPTN-
3 fixed maximum amount of nitrogen (46.92 mg of N g-1 of sucrose) followed by
HVKN-6 (32.62 mg of N g-1 of sucrose).
From the invitroexperiment, two most promising isolates each of IAA
producers, phosphate solubilizers and nitrogen fixers were selected for preliminary
screening for growth promotion on blackpepper cuttings. The isolate HPLPSB-3 (P
solubiliser) recorded maximum sprouting, vine length, number of leaves, number of
roots and roots fresh weight underinplanta screening for plant growth promotion.
However, maximum root length was observed in HPLBC-6 (IAA producer).
All the isolates were screened in vitro for their antagonistic activity against
foot rot pathogen Phytophthora capsici. Among the bacteria, isolate HPLPSB-6
recorded maximum inhibition (69.27 %) of the pathogen. Among the actinomycetes,
HVZACT-1 recorded maximum mycelial inhibiton of 66.66 %. Among the fungal
isolates screened, maximum inhibition (75.17 %) was recorded by the isolate FPRF-3.
The three most promising PGPM selected from preliminary in planta
screening and three antagonists from in vitro screening were further tested for their
efficiency in controlling foot rot disease in blackpepper nursery. Minimum disease
incidence (6.23%) and severity (4.00 %) were observed in isolate FPRF-3. This was
followed by actinomycete HVZACT-1 with disease incidence of 13.20 % and
severity of 8.00 %. Maximum disease incidence and severity were observed in control
with pathogen alone. In addition to biocontrol activity, FPRF-3 also improved plant
growth parameters such as length of vine, number of leaves and roots.
The selected growth promoting isolates HPLPSB-3, HPLBC-6 and YPTN-3
were identified as Acinetobacter grimontii, Providencia sp. and Paenibacillus sp. The
three selected antagonists HPLPSB-6, HVZACT-1 and FPRF-3 were identified as
Paenibacillus polymyxa, Streptomyces termitum and Trichoderma viride respectively.
Based on in planta evaluation, Acinetobacter grimontii was considered as the
best PGPM and Trichoderma viridethe most promosing antagonist against P. capsici.
These isolates could be further exploited for improving the growth and managing foot
rot disease, after validation under field conditions. The compatibility of PGPM with
antagonists and chemical fungicides may also be evaluated.This is the first report of
antagonistic activity of the actinomycete S. termitum against P. capsici causing foot
rot disease in blackpepper.