TY  - BOOK
AU  - Rengima Nambiar
AU  - Yamini Varma C K(Guide)
TI  - Efficacy of pink pigmented facultative methylotrophs for the management of leaf blight disease in Amaranthus (Amaranthus tricolor L.)
U1  - 632.3 
PY  - 2023///
CY  - Vellanikkara
PB  - Department of Plant Pathology, College of Agriculture
KW  - Plant Pathology
N1  - MSc
N2  - 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
ER  -