In order to find out the interaction effect among the three species of Rhizoctonia namely, R. solani, R. oryzae and R. oryzae-sativae, subsequently two 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.
In laboratory condition, the antagonism among the three fungal pathogens was tested in dual culture method. The interaction between R. solani versus R.
oryute, R. solani versus R. oryzae-sativae and R. oryzae versus R. oryzae- sativae was observed in dual culture in petridishes and found that the radial growth of R. solani was always higher than the growth of R. oryzae and R.
oryzae-sativae starting from 48 to 96 hours period of lime. But the growth of R.·
oryzae or R. oryzae-sativae was more or less similar or followed by each other.
In R. solani versus R. oryzae and R. solani versus R. oryzae-sativae interactions, R. solaui 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 (CGR) of R. solani over R. oryzae and R. oryzae sativae were higher compared to control at72
and 90 hrs after inoculation while the CGR of R. oryzae sativae over Ro was not increased in interaction, R. oryzae versus R. oryzae sativae at three different time intervals. The higher colony growth ratio compared to control indicated the higher antagonistic effect. R. solani showed antagonistic effect on R. oryzae50
and R. oryzae sativae at 72 and 96 hrs respectively, on the other hand, R. oryzae sativae did not show any antagonistic effect on R. oryzae.
In field experiment, eight treatments were tested
under natura]field condition.
The treatments were Rhizoctonia solani + Rhizoctonia oryzae + Rhizoctonia oryzae-sativae, Rltizoctonia oryzae + Rhizoctonia oryzae-sativae, Rhizoctonia solani + Rhizoctonia oryzae, Rhizoctonia oryzae-sativae + Rhizoctonia oryzae, Rhizoctonia solani alone, Rhizoctonia oryzae alone, Rhizoctonia oryzae-sativae alone and control condition.
In case of % RLH and infected tiller, significant differences were found among the treatments. The % RLH and infected tiller in sheath blight were higher in R.
solani alone compared to R. solani+R. oryzae-sativae+R. oryzae, R. solani+R.
oryzae and R. sO/(1J1.i+R.oryzae-sativae treatments. In case of aggregate sheath spot, %RLH and infected tiller were also higher in R. oryzae-sativae alone compared to mix with both R. solani and R. oryzae or any of them. Similar trend was followed in sheath spot disease.
The highest percentages of RLH and infected tiller were found at maturity followed by hard dough and flowering stage. The development of these three diseases was higher during the later stages of crop growth. Interactions between treatments and growth stages for %RLH and infected tiller showed significant differences. The severity and incidence were greater in sheath blight, sheath spot and aggregate sheath spot, when R. solani, R. oryzae and R. oryzae sativae respectively inoculated alone. The severity and incidence of each disease were hindered very slightly by the inoculum mixed with three or two pathogens in different growth stages of rice.
No significant variation was observed on yield and yield contributing characters except 1000 grain weight. The highest (numerically) yield was recorded in control treatment. Among the three diseases, the higher % of yield losses
occurred when R ..'so/ani inoculated alone or mixed with both R. oryzae sativae and R. oryzae or any of them. Probably sheath blight caused by R. so/ani played a major role for causing yield loss of rice. A very little amount of yield losses occurred due to sheath spot and aggregate sheath spot respectively.
The findings of the present study indicated that R. so/ani, showed antagonistic effect on R. oryzae-satiave and R. oryzae. The severity and incidence of each diseuse were less when two or three pathogens inoculums were mixed in di fferent growth stages of rice.
Considering the situation :llld limitnt ion» of the present invcstigntion. further studies in the following areas may be suggested:
o Repetition of the same experiment is necessary to get definite conclusion.
o Regional trails I,nay be performed in order to find out the location variation.
o Di ffercnces of cropping season may be evaluated.
,"
52
-
"
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63
Appendices
APPENDICES
Appendix 1. Results of mechanical and chemical analysis of soil of the experimental plot
Mechanical analysis
Constituents Percent
Sand 33.50
Silt 60.20
Clay 6.20
Textural class Silty loam
Chemical analysis
Soil properties Amount
Soil I'll 6.08
Organic carbon ('Yo) 1.3
Total nitrogen (%) 0.08
Available P (ppm) 20
--
- ----- -
L:xchallgcablc K('10) 0.2
Appendix II. Monthly average temperature, relative humidity and total rainfall of the experimental site during the period from November 2005 to May 2006
Month Air temperature (ue) RH(%) Total Sunshine
Maximum Minimum 9am 2pm rainfall (hrs/day)
(mm)
November 05 29.5 18.7 76.1 59.6 5.2 7.0
December 05 27.5 14.4 73.1 52.6 0.0 7.5
January 06 25.5 12.4 78.8 45.9 0.0 6.7
February 06 31.1 18.4 76.0 45.3 0.0 7.2
March 06 33.6 20.1 67.8 39.8 0.0 8.4
April 06 33.6 22.8 77.7 61.0 95.2 7.6
May 06 34.0 24.8 77.3 62.8 465.0 6.4
64 ., •
Appendix III. Analysis of variance of the data on
%RLH and
%infected tiller. on sheath blight, sheath spot and aggregated sheath spot pooled over three growth stages
Sources of Degrees Mean ~guare
variation of Sheath blight Sheath spot Aggregate sheath
freedom spot
%RLH % %RLH % %RLH %
infected infected infected
tilIer tiller tiller, .
Rcplicai ion 2 2.~:15 17.:n5 O.:'\5<l 19.15~ 11.260 1.982
Treatment (A) 7 755.61 ** 4305.8** 3149.1
**
705.8** 3016.1** 586.2*'"EITor 14 11.613 44.433 14.362 10.364 8.938 2.S81
Growth stage (B) 2 10933.8** 3477.4** 1760.9** 154.0** 2043.1** 163.6**
Interaction 14 157.49** 285.02** 254.56** 21.72** 228.46** 20.92**
Pooled error 32 4.240 3.335 3.022 0.256 1.739 0.963
...: Significant at 0.0 I level ofsignificance