MSc

The study entitled “Integrated management of Rhizoctonia leaf blight of
Amaranthus (Amaranthus tricolor L.)” was conducted at the College of Agriculture,
Vellayani and Coconut Research Station, Balaramapuram during 2014-2016 with the
objective to investigate the effect of soil solarization, biocontrol agents, chemical
activator, indigenous formulations and new generation fungicides on growth, yield
and severity of foliar blight of amaranthus.
Samples of the infected leaves showing Rhizoctonia leaf blight in amaranthus
were collected from Vellayani, Kalliyoor, Venganoor and Kakkamoola locations.
Among the four isolates of the pathogen, the Vellayani isolate gave significantly
superior growth rate with minimum of six days for sclerotial formation. Koch‟s
postulates were proved for the pathogenicity of different isolates of Rhizoctonia
solani. All the four isolates have taken three days for the first symptom development
but the progression of lesion size of Vellayani isolate was maximum compared to all
other isolates, hence the Vellayani isolate was selected as the most virulent isolate
for use in further in vitro studies.
Evaluation of biocontrol agents for in vitro suppression of R. solani showed
that Trichoderma harzianum completely overgrown the pathogen with maximum
inhibition of 49.56 % compared to Pseudomonas fluorescens (28.30 %). Under in
vitro evaluation of chemical activator, different concentrations of Acibenzolar-S-
Methyl (ASM) against pathogen, 100 ppm concentration recorded the maximum
mycelial inhibition of 75.67 % and 5 ppm concentration recorded the minimum
mycelial inhibition of 27.70 %. Among indigenous organic formulations, turmeric
powder and baking soda combination inhibited the maximum growth of the
pathogen by 64.40 %. In the in vitro studies with new generation fungicides,mancozeb in cow dung supernatant (0.4 %) and tebuconazole (0.1 %) recorded the
100 % mycelial inhibition of the pathogen.
Field studies on disease suppression and plant growth promotion was carried
out as two experiments, one in soil solarized plots and the other in non solarized
plots. Soil solarization along with soil application of ASM (75 ppm) and foliar
application of ASM
(100 ppm) recorded the lowest disease incidence of 30.41 %
and 30.42 % respectively, which was superior when compared with foliar application
of ASM (100 ppm) and soil application of ASM (75 ppm) with the disease incidence
of 37.06 % and 38.84 %.
Soil solarization + foliar spray of tebuconazole (0.1 %) recorded the minimum
disease index of 37.85 % which was superior compared to foliar spray of
tebuconazole (0.1 %) with the disease index of 39.28 %. Among the biocontrol
agents soil solarization + foliar spray of Pseudomonas fluorescens (2 %) gave
minimum disease index of 45.22 % which was greater compared to foliar spray of P.
fluorescens (2 %) with the disease index of 51.66 %. In case of indigenous organic
formulations, soil solarization + foliar spray of fish amino acid (5 %) given the
maximum control of the disease with the disease index of 49.51 % which was
superior to foliar spray of fish amino acid (5 %) with disease index of 63.59 %.
The number of days taken for flowering in soil solarized plots ranged from
28.67 to 35 days where as the number of days taken for the flowering of amaranthus
in non solarized plots was ranged from 27.27 to 31.67 days.
At the time of harvest, soil solarization + mancozeb in cow dung supernatant
(0.4 %) recorded maximum plant height of 127.07 cm which was higher compared
to foliar spray of azoxystrobin (0.15 %) with plant height of 117.60 cm. Maximum
of 78.00 number of leaves were recorded by soil solarization + foliar spray of
azoxystrobin (0.15 %) which was greater compared to foliar spray of azoxystrobin
(0.15 %) with 67.67 number of leaves.Soil solarization + foliar spray of azoxystrobin (0.15 %) gave the highest yield
in terms of fresh weight by 26975.00 kg/ha and dry weight of 4233.33 kg/ha which
was superior when compared with foliar spray of tebuconazole (0.1 %) with the fresh
weight of 23375.00 kg/ha and dry weight of 3362.50 kg/ha.
It is concluded that soil solarization for 31 days with the foliar application of
tebuconazole (0.1%) can effectively control the Rhizoctonia leaf blight disease
severity with plant growth and yield promotion under field conditions.