Abstract:
Experiments were conducted both in laboratory and experimental field of Plant
Pathology Division of Bangladesh Rice Research Institute (BRRI), Oazipur
during Boro season, 2005-2006, to find out the interaction among the three
Rhizoctona species namely, Rhizoctonia solani, Rhizoctonia oryzae and
Rhizoctonia oryzae-sativae.
In laboratory condition, the interaction between Rhizoctonia species was
observed in dual culture and found that the radial growth of R. solani was
always higher than the growth of R. oryzae and R. oryzae-sativae. But the radial
growth of R. oryzae or R. oryzae-sativae was more or less similar. In R. solani
versus R. oryzae and R. so/ani versus R. oryzae-sativae interactions, R. so/ani
fused with R. oryzae or R. oryzae-sativae within 24 hours and was slightly
overlapping on R. oryzae and R. oryzae-sativae, respectively at 96 hours. Both
R. oryzae and R. oryzae-sativae were comparatively slow growing fungi. R.
oryzae fused with R. oryzae-sativae at 96 hours but no overlapping was
recorded within this period. In interactions, R. solani versus R. oryzae and R.
solani versus R. oryzae sativae, the colony growth ratios (COR) of R. solani
over R. oryzae and R. oryzae sativae were higher compared to control at 72 and
96 hrs after inoculation indicating positive antagonistic effect on R. oryzae and
R. oryzae sativae. R. oryzae sativae did not show any antagonistic effect on R.
oryzae.
In field experiment, % relative lesion height (RLH) and % infected tiller were
significantly differed among the combination of R. solani, R. oryzae and R.
oryzae-sativae or either of two or each alone. The % RLH and % infected tiller
in sheath blight were higher in R. solani only. In case of aggregate sheath spot,
0/0 RLH and infected tiller were also higher in R. oryzae-sativae alone compared
to mixed with both R. solani and R. OIJ1zae or any of them. Similar trend ·was
followed in sheath spot disease. The highest percentage of RLH and infected
tiller were found at maturity followed by hard dough and flowering stage.
Inoculation of three pathogens, R. solani, R. oryzae and R. oryzae sativae alone
evidenced the highest disease severity and incidence compared to combination
of three or any of two pathogens in three-growth stages (flowering, hard dough
and maturity). The severity and incidence of each disease were inhibited very
slightly by the inocula mixed with three or two pathogens. No significant yield
losses was observed in combination of three pathogens or mixed with two or
each alone. Among the three diseases, the higher % of yield losses (13.86-18.93
%) occurred when R. solani inoculated alone or mixed with both of R. oryzae
sativae and R. oryzae or any of them.
Description:
A Thesis
Submitted to the Faculty of Agriculture,
Sher-e-Bangla Agricultural University, Dhaka
in Partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE (MS)
IN
PLANT PATHOLOGY