Studies on cotton root rot incited by Macrophomina phaseolina (Tassi) Goid
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Date
2017
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CCSHAU
Abstract
Cotton root rot disease caused by Macrophomina phaseolina (Tassi) Goid. is one of the most important soil
borne disease of cotton in India. In the present investigations an effort was made to find out the efficacy of
different fungitoxicants and antagonists under in-vitro and screen house conditions and the effect of temperature
on different isolates of M. phaseolina. Carbendazim and MEMC at 10ppm concentration gave 100% mycelial
growth inhibition of M. phaseolina in vitro. Five isolates of Trichoderma spp. were evaluated against M.
phaseolina in vitro. T. viride – I was observed the most effective as it caused maximum growth inhibition
(71.1%) of the pathogen followed by T. harizianum – II (62.6%). Seed treatment of cotton with the antagonists
along with compost significantly reduced the pre and post emergence mortality due to M. phaseolina under
screen house condition. It was found that in both American and Desi cottons, seed treatment of T. viride + soil
application of T. viride incubated in FYM was better in controlling the disease as it exhibited 56.9–68.2 per cent
disease control in A. Cotton and 64.9–62.3 per cent disease control in Desi cotton. The effect of fungitoxicants
against cotton root rot was investigated under screen house condition in American cotton and Desi cotton. It was
found that in both the cottons seed treatment with carbendazim was best in controlling the disease as it exhibited
68–78.3 per cent disease control in American cotton and 75.5–82.8 per cent disease control in Desi cotton.
Colony colours of the six isolates of M. phaseolina were variable on two media i.e. PDA and CDA. Colonies of
isolates were grey, dark grey, or black. The white colony colour was observed at lower temperature i.e., 15°C
and 20°C on both media. Black colour colonies of all the isolates were noticed at 35°C in both the media
indicating that the fungus grows at slower rate at low temperature. At 72 hrs of measurement the M. phaseolina
exhibited maximum growth on PDA medium. PDA medium was the more favourable for mycelial growth and
CDA medium was for favourable for microsclerotia size of this pathogen. Substantial differences in diameter
between microsclerotia of the same isolate on different media were observed. The diameter of Sclerotia ranged
from 74 to 120 μm in PDA and CDA. Size of sclerotia in both media did not vary with variation in temperature.
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