STUDIES ON THE INTERACTION AMONG Rhizoctonia solani, Rhizoctonia oryzae AND Rhizoctonia oryzae-sativae CAUSING SHEATH DISEASES OF RICE

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.