Rice blast caused by Magnaporthe grisea is turn to be one of the most severe pathogen under change in climatic condition in coastal region of South-Eastern India. Severity of the pathogen was not overwhelming previously. An investigation was carried out in several villages of different districts of Andhra Pradesh and Odisha under the RAWEP programme of Centurion University of Technology and Management with compared to meteorological data support from IMD, Bhubaneswar, Odisha. Different meteorological factors consider under this study were maximum temperature (Tmax), minimum temperature (Tmin), relative humidity maximum (RH max), relative humidity minimum (RH min), rainfall (RF). Among the three cultivated rice varieties, Pooja and Samba mahsuri (BPT-5204) are the most susceptible blast varieties (5.71% and 4.85%) compared to Swarna (MTU 7029) with a disease incidence level of 1.23%. Outcome of this investigation also revealed that the most crucial two (Tmax and RH max) factors directly involved for the emergence of the disease compared to previous year 2015-16 and 2016-17. The peak disease infestation was observed in the month of October and November with PDI of 27.33 % and 26 %. Farmers based prolonged survey report and our observation concluded with the fact that Tricyclazole 75% WP (trade name BAAN/ Indofils) and 40% EC formulation of Isoprothiolane (trade name Fujione / Rallis India Limited) are the two sequential most effective fungicides compared to different market based available fungicides and showed best efficacy against neck, collar and leaf blasts. Weather parameters as well as complex adaptability of the pathogenic nature (showing resistant against different fungicides) turned this Ascomycota member to a severe one.
Rice is one of the most important major food crop in South Eastern India. Asian countries are main rice producer as well as consumer of world 90% production. The main rice producing countries are India, Bangaladesh, China, Thailand, Philippines, Myanmar, Japan. Rice cultivation is the major activity and source of income for millions of households round the globe (Magar
Agro-climatic condition, which prevailed in this region, are crucial and most important to act as a green corridor system for upcoming biotic and abiotic stresses on crop health. Under biotic stresses numbers of fungi, bacteria, viruses, nematodes and non-parasitic disorders are involved among which rice blast is one of the major important biotic stress, which acts as a limiting factor for rice production. Blast of rice was first introduced in this region in long past at Tanjore district of Tamil Nadu in 1918 (Pradhan et al. 2018). Rice blast pathogen is a devastating pathogen and it can cause yield loss ranging from 30-61% depending upon the stage of infection. The most severe form of blast is the Leaf and panicle blast (Zeigler and Correa. 2000). Depending on cultivar susceptibility, environmental conditions and management system, it causes yield losses up to 100% (Ou 1980). The fungus can infects all parts of the shoot (Talbot 2003; Sesma and Osbum 2004) and caused three different symptomatology neck, collar and leaf blast. Symptoms appears as diamond shape or eye shaped brownish lesions encircled with a yellow hallow or scattered darkish outline. Different meteorological factors played a crucial role for rice blast disease development. Sequential changes of weather variables in year after year makes the pathogen more severe and drastic in nature.
Planting of resistant cultivars, application of fungicides, and manipulation of planting times, fertilizers and irrigations are the most usual approaches for the management of this disease (Georgopoulos and Ziogas 1992; Moletti
Different host farmers were selected from different agro-ecological region by the RAWE students (
Geographical Location of Different villages selected under RAWE Programme
Format of questionnaire under RAWE Programme
The survey was done in questionnaire format (
The different types of land (Upland/Lowland/Medium land) was taken in to consideration for selection of plots. Low land plots were chosen as mainly rainfed rice was growing in the coastal region so that rain water can be harvested in the field itself for the high water required rice crop.
The different disease samples were collected from the 10 above mentioned villages. Assessment of the disease severity was done by 0-5 point index scale (Inglis
Scale 0- No symptom
Scale 1- Greyish green lesion with dark green border (>10%)
Scale 2- Spindle shaped whitish to gray centers with necrotic border (> 20-30%)
Scale 3- Coalesce of spots and observation of large patches on leave (>40-60%)
Scale 4- Observation of Neck and node blast (>70-80%)
Scale 5- Burning appearance of total plant, lodging and dying of the plant (>90%)
The pathogen was isolated from the collected sample which was showing more disease severity. Isolation of pathogen was carried out by using Oatmeal Tomato Agar (OTA) media. For preparation of this media, 25g of oatmeal was boiled with 500ml of water and then filtered. Agar powder (12.5g) and Tomato juice (94ml) was mixed with the filtered solution and autoclaved at 15lb psi for 15min (Li-wang
After isolation of the pathogen successfully in OTA media, the pathogen was taken in glass slides to observe the spores under compound microscope in different magnification to get confirmation about the pathogen. Before observing the slide, Lactophenol and cotton blue was added in the slide at 1:1 ratio to stain it and see the spores clearly.
From the survey, It was observed that 70% of the farmers were growing rice crop while 20% farmers growing vegetables and rest 10% other crops. From the 70% farmers growing rice variety, 60% were cultivating Samba mahsuri (BPT-5204), 25% pooja variety, 10% Swarna (MTU 7029) variety and rest 5 % other varieties which was clearly mention in the below pie chart (
Percentage of farmers growing different crops and Different varieties of Rice
The meteorological data of last 3 years were collected from Indian Meteorological department, Bhubaneswar. The different factors considered are Temperature maximum (Tmax), Temperature Minimum (Tmin), Relative humidity Maximum (RHmax) and minimum (RHmin), rainfall (RF).
One of the most important methods to control blast disease is to use efficient fungicides (Manandhar 1984; Sah and Karki 1988; Chaudhary 1999). Therefore, the information of use of different management strategy against this disease was collected from the farmers. The different noted fungicides used against blast disease by the farmers were listed in the below mentioned table (
Status of five different market based fungicides selected for efficacy detection against Rice blast
Different statistical analysis was done to correlate the disease severity with the weather condition to know specifically how the blast disease is well dependent upon the climatic variables. For this analysis, different statistical tools were used like Miniab 17, IBM SPSS V.19 etc
Cultural isolate of the pathogen was maintained in BOD under 28-30 C for 48-72 hr. Variation of colony colour ranged from white, light gray, dark brown, black. Smooth to serrated texture, smooth edges at the periphery, sometimes metabolites found. Microscopical observation stated that shape of the conidia as typically pyriform with rounded base, apex narrowed, 2-3 septate/2-4 celled. The colour of the conidia ranged between pale olive to brownish to hyaline. Some of them were very long and narrow, while some were much broader with 2 septa. Conidial size ranged between 25-30 µm (l) ₓ 4-8 µm (b). Conidia are produced from sympodial manner from conidiogenus proliferating cells. The pathogen can sporulate from the host surface and form a scattered surface. Sometimes the aerial mycelia will present, it appears to be branched and hyaline to olivaceous. The newly raising conidiophores are simple to rarely branched that are moderately long and septate. Conidiophores are brownish in colour, denticles are sometimes found on the terminal position (
Disease severity data in the form of percent disease index (PDI) were comparatively analyzed between 2015-16 to 2017-18. Outcome of this analysis revealed that blast disease severity was higher (19.7%) in 2017-18 compared to 2015-16 (17.6%) and 2016-17 (18.3%), as well as time series analysis of the disease data showed highest disease severity percentage in October-November, followed by September, December, August and July (
Different weather variables (
Construction of heat map based on percent disease index from 2015-16 and 2017-18
Trend of Blast disease severity in July to December from 2016-17 to 2017-18 through time series analysis
Different weather variables were correlated with blast disease severity (PDI) (simple correlation with PDI and cross correlation with different factors) from 2015-2018 and found to be significant at 0.01 and 0.05 level. Statistical analysis were performed under Minitab version 17. Weather variables and PDI value were correlated and largest possible variance were measured under orthogonal transformation procedure or by analyzing principal component analysis. Yearly disease prediction from 2015-16 to 2017-18 was analyzed with interaction between weather variables with PDI through multiple regression equation (Fitted line equation) and depicted under
Weather variables from 2015-16 to 2017-18 and their consecutive rice blast disease severity (PDI) per month basis
Multiple Regression equation (Fitted line Equation) for prediction of rice blast disease severity
Yearly average of weather variable correlation with PDI
Correlation with Tmax and PDI under residual vs fitted graph
Correlation with Tmin and PDI under residual vs fitted graph
Correlation with RH1 and PDI under residual vs fitted graph
Correlation with RH2 and PDI under residual vs fitted graph
Correlation with Rainfall and PDI under residual vs fitted graph
Efficacy detection of five market based fungicides and their interaction with varietal tolerance
Comparison of disease tolerance superiority of Swarna than Pooja and Samba Mashuri through interval plot
Blast tolerant rice variety selection among cultivated varieties depends on nature of susceptibility. Among the three cultivated rice varieties, Pooja and Samba Mahsuri (BPT-5204) are the most susceptible blast varieties (5.71% and 4.85%) compared to Swarna (MTU 7029) with a disease incidence level of 1.23%. Again this three varieties were treated under different types of commercial chemical fungicides and their disease severity, disease control (%) were depicted under the
Different market based fungicides were evaluated to control different types of blast symptoms under field conditions and their ultimate effects on productivity. During the experiment leaf blast severity was found to be significantly less by using some specific fungicides, where as in other cases the severity was not downwards or more (without treatment). Among the five selected fungicides, Tricyclazole 75% WP (trade name BAAN/ Indofils) and 40% EC formulation of Isoprothiolane (trade name Fujione / Rallis India Limited) are the two sequential most effective fungicides compared different market based available fungicides and showed best efficacy against neck, collar and leaf blasts. Results of the experiment shown under the
Rice blast is one of the most severe disease in South eastern India. Variable epidemiological factors affect greatly on the disease establishment, development and severity resulting in huge crop loss. It was evident from the studies of simple correlation co-efficient between weather variables and PDI that maximum temperature, maximum relative humidity and rainfall were positively and significantly correlated with PDI i.e. the increment of rainfall and maximum relative humidity additionally interaction between this two factors and maximum temperature enhanced leaf blast disease by constructing one triangular pool. Nearly 30-35 degree temperature with high moisture (80-90%) and scattered rainfall (120-150 mm) helps in disease progress. As par Vishwanath and Channamma (1988) blast pathogen prefers optimum temperature and with high humidity and heavy rainfall for outbreaks. As par Bhatt and Chauhan (1985) observed that minimum temperature, more number of rainy days, higher rainfall are the most crucial factors of which favored blast disease. Patel and Tripathi, 1998 and Pall, 1988 reported nearly 22-29 C temperature with 85-99 per cent RH was act as a triggering factor for the blast. In 1994, Jain et al. reported moderate temperatures (21-29 C) with more than 80% mean atmospheric relative humidity during reproductive period favored the disease development, which is in conformity with our recent findings. Prediction equation from 2015-16 to 2017-18 can be used for forecasting leaf blast disease severity and can be used as a component of Integrated Disease Management (IDM) programme by decreasing the use of chemical spray as a control measure and used as a forecasting machinery under RAWEP programme. Therefore, it is concluded from the experimental results that, out of five independent weather variables considered under this research or prediction of PDI, maximum temperature, maximum RH and maximum RF were identified as critical weather parameters following principal component analysis. All the independent factors are somehow positively, negatively or partially correlated with disease severity. Effect of different fungicides to control blast disease were tested under this research under positive interaction with three mostly cultivated varieties. Magar et al. in 2015 found Tricycazole 22% and Hexaconazole 5 % combination is the best effective fungicides against blast disease and got more yield after applying the same. we have observed quite similar result by our research, where Tricyclazole 75% WP (trade name BAAN/ Indofils) and 40% EC formulation of Isoprothiolane (trade name Fujione / Rallis India Limited) are the two sequential most effective fungicides compared different market based available fungicides and showed best efficacy against neck, collar and leaf blasts with good yield. Environment itself as a laboratory of its own, we are not encouraging to farmers to use chemical measure, as because it is very much harmful for sustainable agriculture but it can useable as an IDM component when the disease is not manageable or very severe stage.
We would like to thank Prof. D.N. Rao (Vice President), Prof. Supriya Pattanayak (Vice Chancellor), Prof. S.P. Nanda (Dean) for giving a platform as a programme supervisor under RAWEP scheme at Centurion University, additionally IMD, Bhubaneswar, Odisha for their meteorological data support.