MSc

Amaranthus (Amaranthus tricolor L.), ("poor man's spinach") is one of the
widely cultivated tropical leafy vegetables of Southern India. It is attacked by the most
destructive disease, leaf blight by Rhizoctonia solani Kuhn, causing more than 90 per
cent of yield loss. Chemical management of this pathogen causes health hazards due
to pesticide residue. PPFM naturally occurring on the phyllosphere of amaranthus have
great value in giving protection against leaf diseases, on which no detailed systematic
studies have been conducted in Kerala.
In this context, the present study was undertaken with the objectives of
identification of Pink Pigmented Facultative Methylotrophs (PPFM) from amaranthus
phyllosphere and to evaluate their efficiency for the management of leaf blight disease
in amaranthus. The experiment was carried out in Pepper Research Station, Panniyur,
during March 2022 – November 2022.
Purposive sampling surveys were conducted in amaranthus growing fields of
five different AEUs in Kannur district of Kerala viz.Thalassery, Kuttiyattoor, Panniyur,
Punnad and Kanichar from April to May, 2022. The disease incidence and severity
were maximum in the Kuttiyattoor area with 89.40 and 74.60 per cent, respectively.
The fungus was isolated from leaf samples and the pathogenicity was proved.
Symptomatology was studied both under natural and artificial conditions. The fungus
was characterized and identified as Rhizoctonia sp. by studying their cultural and
morphological characteristics. Highly virulent isolate, LB-3 was selected for further
studies. PCR amplification of large subunit (LSU) region of the fungal genome
followed by sequencing and in silico analysis confirmed that the suspected fungus, LB3
as Rhizoctonia solani.
A total of 10 isolates of Pink Pigmented Facultative Methylotrophs (PPFM)
from amaranthus phyllosphere were isolated and cultural, morphological and
biochemical characterization was done. All the isolates were screened for their
antagonistic potential against selected R. solani using dual culture technique. PPFM-2
and PPFM-5 showed 53.18 and 53.69 (in solid medium) and 77.77 and 74.04 (in liquid
broth) per cent inhibition respectively. Hence, these two most promising isolates were
selected for further field studies. The bacterial isolates PPFM-2 and PPFM-5 were
confirmed as Microbacterium testaceum and Methylobacterium hispanicum through
the amplification of 16S rRNA region of the genome followed by sequencing and in
silico analysis.
Under in vitro conditions, antagonistic activity of PPFM-2 and PPFM-5 were
compared with biocontrol agents, botanical and fungicide against R. solani. Dual
culture assay showed that PPFM-2 (52.77 %) and PPFM-5 (53.88 %) were more
effective than Pseudomonas fluorescens (43.42 %) and less effective than Trichoderma
asperellum (72.50 %) for inhibition of R. solani. Poisoned food technique showed that
PPFM-2 and PPFM-5 were in line with mancozeb 75 WP, as both showed 100 per cent
inhibition to R. solani. And they were more effective than Raksha at 0.6 (36.00 %), 1.0
(74.40 %) and 2.0 (82.20 %) per cent concentration.
Efficacy of selected strains of PPFMs (M. testaceum and M. hispanicum),
biocontrol agents (T. asperellum and P. fluorescens), botanical (Ready to Use Neem
Oil Garlic Soap, Raksha) and fungicide (Mancozeb 75 WP) against R. solani under field
conditions were tested. The natural disease incidence in the field was delayed to 28 days
by M. hispanicum and to 23 days by M. testaceum. Maximum per cent reduction over
control for disease incidence and disease severity was showed by M. testaceum and M.
hispanicum.
Biometric observations at 30, 45 and 65 days after transplanting, showed
maximum increase over control for plant height, number of leaves per plant, fresh and
dry weight of shoots and shoot root ratio in PPFM treated plots. In contrast, the root
length as well as fresh and dry weight of roots were maximum in P. fluorescens
treatment. Recording the PPFM population in the phyllosphere at harvest, it is revealed
that plants with the highest population of PPFM displayed significantly enhanced
biometric characters as compared to plants with a substantially lower population.