VARIABILITY OF Rhizoctonia solani Kuhn INFECTING SMALL MILLETS AND THEIR MANAGEMENT
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Date
2019
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Birsa Agricultural University, Ranchi
Abstract
Rhizoctonia solani Kuhn (Teleomorph: Thanatephorus cucumeris) is a soil borne,
polyphagous, necrotrophic plant pathogenic fungus with a wide host range. It is causing sheath
blight disease on a wide range of Graminae plant hosts and causes considerable losses in yield. The
pathogen is genetically diverse showing variability in respect of cultural/ morphological and
physiological characters.
100 isolates of Rhizoctonia solani were obtained from four different small millets
showing typical symptoms of the disease. Among them, only 53 isolates were selected and
designated based on their growth characterisics and respective host for intensive characterization.
Studies on morphological character of different isolates of R. solani revealed that the
variation with respect to hyphal width, distance between the septation and mycelial weight. Hyphal
width of most of the isolates were having moderate to long width (5-10 μm). In foxtail millet
isolates, distance between septation is more when compared to remaining isolates. Mycelial weight
is maximum in finger millet isolates.
Studies on cultural variability showed considerable variation among the isolates. The
colony diameter is varied from 41.33-90 mm at 72 hrs of incubation. Majority of the isolates of
foxtail millet and finger millet were slow growing whereas isolates of proso millet and little millet
were fast and medium growing. The colony colour varied from white, light brown to brown.
Concentric circle is present in most of the isolates of foxtail millet and finger millet and it is
completely absent in proso millet and little millet isolates. Dispersion of mycelium varied from
subdued to aerial growth. Studies on sclerotial bodies revealed that, sclerotial formation is absent in
12 isolates. Number of sclerotia per plate were varies from 11-138, in which foxtail millet isolates
produced more number of sclerotia with minimum size and weight. Majority of the isolates have
brown coloured sclerotia with round shape and smooth surface. In arrangement of sclerotia, foxtail
millet and finger millet isolates showed greater variation with different patterns of arrangement viz.,
peripheral, central, central+peripheral, concentric circle or uniformly/scattered distributed.
Studies on pathogenic variations revealed that variation observed in accordance with the
latent period, lesion size and lesion shape. Cross inoculation studies revealed that most of the
isolates of R. solani were cross infective with each other and all the proso millet isolates were
highly pathogenic on foxtail millet.
Host range studies unveiled that majority of the isolates successfully infect rice, sorghum,
soybean, bajra except groundnut but their virulences on different crops were quite different. It was
observed that slow growing isolates of foxtail millet, finger millet and little millet were more
aggressive than medium and fast growing isolates.
Sensitivity of fungicides against 12 isolates showed that at 0.1% conc. triazole fungicides
(propiconazole, difenconazole and tebuconazole) completely inhibited the mycelial growth and
sclerotial production. In further evaluation of triazole fungicides at 0.05% conc. propiconazole &
tebuconazole showed significant inhibition in mycelial growth and sclerotia.
Among the botanicals, clove extract of Allium sativum (Garlic) showed maximum
mycelial growth inhibition. Bulb extract of Allium cepa (Onion) and rhizome extract of Zingiber
officinale (Ginger) effectively reduced the sclerotial production.
Among bio-control agents, Trichoderma harzianum (T. harzianum-H) procured from
hyderabad showed maximum inhibition of mycelial growth whereas in field evaluation, soil
application of value added Pseudomonas fluorescens + Trichoderma viride + Bacillus subtilis 335
g each of talc formulation mixed in 25 kg of FYM at the time of sowing recorded least banded
sheath blight incidence of with highest grain yield in little millet and foxtail millet.
Description
VARIABILITY OF Rhizoctonia solani Kuhn
INFECTING SMALL MILLETS AND THEIR
MANAGEMENT