To develop a disease forecasting model for bacterial leaf blight on rice and its management through plant extracts, antagonists and chemicals.
Development Of A Bacterial Leaf Blight Of Rice Disease Predictive Model Based On Five Years Environmental
And Disease Severity Data
Weekly environmental data consisting of air temperature (°C) (max/min), rainfall (mm), relative humidity (%) and wind speed (km/h) during September-October 2004-2008 were used to develop bacterial leaf blight (BLB) disease predictive model. Stepwise regression was used to determine the influence of environmental variables on BLB recorded on Super basmati, Bas. 385 and Bas. 2000 grown continuously for five years at RRI, KSK and NIAB. The data of BLB disease severity of other varieties i.e. Bas 370 and Bas Pak at NIAB and KSK 282 and IRRI 9 at RRI, KSK was also employed as dependent variable. The environmental conditions during five years differed significantly at two locations. The susceptible to highly susceptible reaction of rice varieties to BLB at two locations however, did not differ significantly. Majority of environmental variables (air temp max/min and rain fall) had significant correlation with BLB disease severity at both the locations, however, the degree of correlation increased when the data were split by years. Based on five years data a model consisting of all the five environmental parameters explained 64 and 54 percent of the variability in BLB disease development at NIAB and RRI, KSK, respectively. When these data were split by year different models emerged at both locations. At NIAB a three environmental variable model consisting of air temperature and wind movement explained 98% of the variability in BLB disease severity during 2005, 2007 and 2008 while two environmental variable model consisting of relative humidity and wind speed during 2004 and three variable model (relative humidity, wind speed and rainfall) during 2006 explained 94% and 98% of the variability in BLB disease development, respectively. A three environmental variable model consisting of air temperature (max/min) and relative humidity explained 97, 99 and 95% of the variability in BLB disease development during 2004, 2005 and 2006 at RRI, KSK respectively. During 2007 and 2008, minimum air temperature, relative humidity and wind speed explained 96 and 99% of the variability in BLB disease severity at this location. Maximum BLB at RRI, KSK was recorded at 35-38 and 26-27 °C max and min air temp., 61-72% relative humidity, 1-12 mm total rainfall and 3-5 km/h wind speed, while at NIAB maximum BLB was recorded at 33-37 and 20-23 °C max and min air temp, 35-59% relative humidity, 0.73-13 mm total rainfall and 3-5 km/h wind speed. Advance warning forecasts to rice growers can be issued at these critical ranges of the environment to support management decisions for the control of BLB.
Testing Of Bactericides, Fungicides, Biopesticides And Other Potential Chemicals For Blb Control
Experiments were conducted in laboratory (D-177) of Department of Plant Pathology in completely randomized design (CRD) with four replications. Fifteen chemicals i.e., Copper oxychloride, Cuperous oxide, Ridomil Gold, Defeater, Kumulus, Thiovet jet, Success, Alliette, Antracol, Karzate, Cordat, Flare, Score, Agrimycin 100 and, Streptomycin sulphate were tested on nutrient agar through inhibition zone technique. Out of 15 chemicals tested at 0.1, 0.2 and 0.3% concentration against the multiplication of Xanthomonas oryzae pv oryzae Copper oxychloride, Cuperous oxide, Kumulus, Agrimycine 100 and Streptomycine sulphate showed activity against the bacterium indicated by the inhibition zones recorded 48 and 72 hours after inoculation. The other ten chemicals did not show any activity. The best three chemicals effective at 0.2% concentration in ranking order were Agrimycin 100, Copper oxychloride and Streptomycine sulphate respectively.
Testing Of Antagonistic/Allelopathic Effect Of Different Fungi And Bacteria And Plant Extracts For Blb Control
Experiments were conducted in laboratory (D-177) of Department of Plant Pathology in completely randomized design (CRD) with four replications. Fifteen antagonists i.e., Bacillus subtilis, Aspergillus niger, Aspergillus flavus, Pseudomonas flourescens, Botrydiplodia theobromae, Azospirillum sp. Azotobactor sp. Fusarium oxysporum sp. Fusarium semitectum, Trichoderma harzianum, Aspergillus fumigates, Pseudomonas putida, Pseudomonas aeruginosa Trichoderma viridae and pseudomonas flourescens strain No. 5 were tested against in vitro multiplication of X. oryzae pv oryzae. Out of 15 antagonists B. subtilis, A. niger, A. flavus, P. flourescens, T. harzianum, P. putida, P. aeroginosa showed activity against the bacterium compared to untreated control. The other eight antagonists did not show activity against the bacterium. The best three in ranking order were Bacillus subtilis, Pseudomonas flourescens and P. aeruginosa against the BLB pathogen, respectively.
In vitro testing of 15 plant extracts for their efficacy to control bacterial blight pathogen was conducted in CRD with four replications. The fifteen plant extracts/allelochemicals were Neem, Dathura, Akk, Fline, Sorghab, Eucalyptus, Sunfab, Brassica, Mango, Onion, Jaman, Axiom, Vampire, Ginger, and Garlic. Six plant extracts i.e., Neem, Dathura, Akk, Mango, Onion and Garlic were somewhat effective in controlling the BLB pathogen. Others did not show any activity against the pathogen. The best three in ranking order were Garlic, Neem and Dathura extracts compared to untreated control, respectively.
Offseason Tunnel Experiment
Basmati 2000 was grown on February 2, 2010 in a plastic tunnel. The experiment was conducted in completely randomized design with four replications. All these plants were artificially inoculated with a suspension of Xanthomonas oryzae pv. oryzae @ 108cfu/ml as determined by dilution plate technique. The inoculation was done on 27-3-2010 and the treatments (all the above mentioned chemicals, antagonists and plant extracts showing activity against the bacterium in vitro) were applied after 24 hours and the data on disease severity were recorded on weekly basis starting from the initial appearance of bacterial blight disease symptoms.
The disease ratings taken four times were subjected to analysis of variance and the treatment means were compared with the help of least significant difference test. There was a great variation in the disease severity data; however, those treatments which were effective in consistently reducing the BLB significantly compared to untreated control were Copper oxychloride, Cuperous oxide and Kumulus in that order. Agrimycine 100 and Streptomycine sulphate very effective in lab were not so effective in field grown plants. Among the antagonists, Bacillus subtilis and Pseudomonas spp performed well in controlling disease severity. Garlic extract was found to be most effective in controlling BLB pathogen followed by Neem and Dathura in that order. However, phytotoxic effect of these extracts was observed in the form of burning and withering of plants.
Conclusion: Copper oxychoride is readily available in the market and economical also. The extracts of Garlic, Neem Datura need to be standardized to avoid phytotoxic injury. Bacillus subtilis hold good promise for the control of BLB pathogen. The real test of Copper oxychloride, Garlic extract and Bacillus subtilis or other effective treatments demands their application in farmers field under natural inoculum conditions. The treatments performing well in lab or in controlled conditions in greenhouse/plastic tunnel may fail keeping in view the aggressive virulences of the bacterium under field conditions.
Recommendations to the Rice Growers:
1. Three applications of Copper oxychloride or Cuperous oxide at an interval of 10-15 days depending on initial appearance of BLB symptoms will be a good management strategy to control bacterial blight.
2. This year the bio-control technology (application of garlic/neem/dathura extract or Bacillus subtilis) will be tested at farmers field at five locations. The large scale application of the effective treatment will also be done at 10 selected locations in rice growing areas to benefit the farmers to get rid of BLB from the rice field especially Super Basmati or Basmati 2000.
3. Maximum BLB can be expected at 35-38 and 26-27 °C max and min air temp., 61-72% relative humidity, 1-12 mm total rainfall and 3-5 km/h wind speed, while at some locations maximum BLB may occur at 33-37 and 20-23 °C max and min air temp, 35-59% relative humidity, 0.73-13 mm total rainfall and 3-5 km/h wind speed. Advance warning forecasts to rice growers can be issued at these critical ranges of the environment to support management decisions for the control of BLB.