Experiments were conducted both in laboratory and experimental field of Plant
Pathology Division of Bangladesh Rice Research Institute (BRRI), Gazipur
during Boro season, 2005-2006, to find out the interaction among the three
Rhizoctonaspecies namely, Rhizoctonia solani, Rhizoctonia oryzae and
In laboratory condition, the interaction between Rhizoctoniaspecies was
observed in dual culture and found that the radial growth of R. solaniwas
always higher than the growth of R. oryzaeand R. oryzae-sativae.But the radial
growth of R. oryzaeor R. oryzae-sativaewas more or less similar. In R. solani
versus R. oryzaeand R. solaniversus R. oryzae-sativaeinteractions, R. solani
fused with R. oryzaeor R. oryzae-sativaewithin 24 hours and was slightly
overlapping on R. oryzaeand R. oryzae-sativae, respectively at 96 hours. Both
R. oryzaeand R. oryzae-sativaewere comparatively slow growing fungi. R.
oryzaefused with R. oryzae-sativaeat 96 hours but no overlapping was
recorded within this period. In interactions, R. solaniversus R. oryzaeand R.
solaniversus R. oryzae sativae,the colony growth ratios (CGR) of R. solani
over R. oryzaeand R. oryzae sativaewere higher compared to control at 72 and
96 hrs after inoculation indicating positive antagonistic effect on R. oryzaeand
R. oryzae sativae. R. oryzae sativaedid not show any antagonistic effect on R.
In field experiment, % relative lesion height (RLH) and % infected tiller were
significantly differed among the combination of R. solani, R. oryzae and R.
oryzae-sativaeor either of two or each alone. The % RLH and % infected tiller
in sheath blight were higher in R. solanionly. In case of aggregate sheath spot,
% RLH and infected tiller were also higher in R. oryzae-sativaealone compared
to mixed with both R. solaniand R. oryzaeor 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. oryzaeand R. oryzae sativaealone
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 (1 3.86-1 8.93
%) occurred when R. solaniinoculated alone or mixed with both of R. oryzae
sativaeand R. oryzaeor any of them.