Severity Of Rice Blast Disease Research Articles

A Comprehensive Survey and Assessment of Rice Blast Disease Incidence from Major Rice Growing Districts of Telangana State, India

Aim: The aim of this study was to assess the incidence and severity of rice blast disease caused by Pyricularia grisea in various rice cultivars grown in Telangana State during the kharif season of 2019. Methodology: A purposive disease survey was conducted in major rice-growing areas of Telangana State. Disease incidence and severity were recorded from the tillering to grain hardening stage. Percentage disease incidence and severity were calculated at each sampling location. Additionally, pathogenicity tests were conducted on susceptible rice cultivar TN-1 using different isolates of P. grisea. Results: The study revealed significant variations in rice blast disease incidence and severity across the surveyed areas. Disease incidence ranged from 18.5% in Mancherial to 79.41% in Peddapalli, while severity ranged from 22.2% to 85.1%. All sampled cultivars exhibited varying degrees of susceptibility, with severity scores ranging from moderately resistant (2.0) to highly susceptible (9.0). TN-1 showed the highest blast severity, while WGL 1368 exhibited the least severity. Pathogenicity tests showed significant differences among P. grisea isolates, with reactions on TN-1 ranging from moderately susceptible (4.0 to 5.0) to highly susceptible (8.0 to 9.0). Conclusion: The study highlights the widespread occurrence of rice blast disease in Telangana State and underscores the varying susceptibility levels among rice cultivars. These findings emphasize the importance of continued monitoring and management strategies to mitigate the impact of rice blast disease on rice production in the region.

Epidemiology of Rice Blast (Pyricularia oryzae) Disease in Central Punjab, Pakistan

Rice blast disease (RBD) is mostly controlled by fungicides by the farmers of central Punjab, Pakistan. However, the use of fungicides by the farmers is excessive and ill-advised, resulting in the emergence of new resistant strains of Pyricularia oryzae. The ill-advised employment of fungicides can be timed exploring the role of environmental factors favourable for this disease. The objective of current study was to determine the most favourable weather conditions for RBD in central Punjab, Pakistan, where this crop is mostly cultivated. Environmental factors including maximum and minimum temperatures (max and min temp), rainfall (Rf), relative humidity (Rh) and wind speed (Ws) conducive for RBD were characterized during this study. For this purpose, eight years (2009-2016) RBD severity data of susceptible to highly susceptible genotypes together with environmental data (max and min temp, Rf, Rh and Ws) was collected from Kala Shah Kako (KSK), Rice Research Institute (RRI), Punjab, Pakistan. The genotypes were being cultivated for eight years in randomized complete block design (RCBD), and data was kept on recording during the months of high disease pressure. Data was collected after ten days interval using disease scoring scale developed by International Rice Research Institute (IRRI) during 1996. Simple linear regression models were used to determine the relationship of environmental factors with RBD severity. The variation in RBD severity due to environmental factors was determined using coefficient of determination (R2). In present study, the relationship of max temp, Rf, Rh and Ws with RBD severity was positive, significant and linear, however, the relationship of min temp with RBD severity was negative. Max temp 40-42°C, min temp 21-23°C, Rf 2-3mm, Rh 50-70% and Ws 9-11 Km/h were found to be most favourable environmental conditions for RBD severity. The current research disclosed the significant role of all five environmental factors in the spread of RBD. Thus, future predictive models could be established using these five environmental factors for more accurate prediction of this disease in rice belt of Punjab, Pakistan, to time the application of fungicides.

Bacillus vallismortis TU-Orga21 blocks rice blast through both direct effect and stimulation of plant defense.

Beneficial microorganisms are an important strategy for sustainable plant production processes such as stimulate root exudation, stress tolerance, and yield improvement. This study investigated various microorganisms isolated from the rhizosphere of Oryza sativa L. in order to inhibit Magnaporthe oryzae cause of rice blast, by direct and indirect mode of action. The results indicated that Bacillus vallismortis strain TU-Orga21 significantly reduced M. oryzae mycelium growth and deformed the hyphal structures. The effects of biosurfactant TU-Orga21 was studied against M. oryzae spore development. The dose of ≥5% v/v biosurfactant significantly inhibited the germ tubes and appressoria formation. The biosurfactants were evaluated as surfactin and iturin A by Matrix-assisted laser desorption ionization dual time-of-flight tandem mass spectrometry. Under greenhouse conditions, priming the biosurfactant three times before M. oryzae infection significantly accumulated endogenous salicylic acid, phenolic compounds, and hydrogen peroxide (H2O2) during the infection process of M. oryzae. The SR-FT-IR spectral changes from the mesophyll revealed higher integral area groups of lipids, pectins, and proteins amide I and amide II in the elicitation sample. Furthermore, scanning electron microscope revealed appressorium and hyphal enlargement in un-elicitation leaves whereas appressorium formation and hyphal invasion were not found in biosurfactant-elicitation at 24h post inoculation. The biosurfactant treatment significantly mitigated rice blast disease severity. Therefore, B. vallismortis can be a promising novel biocontrol agent which contains the preformed active metabolites for a rapid control of rice blast by a direct action against pathogen and by boosting plant immunity.

A Machine Learning Technique for Rice Blast Disease Severity Prediction Using K-Means SMOTE Class Balancing

Rice blast disease is strongly dependent on environmental and climate factors. This paper demonstrates the integration of a rice blast disease severity prediction model based on climate factors, providing a decision-support framework for farmers to overcome these problems. The major contribution of the proposed study is to predict the severity of rice blast disease using the linear SVM model. Prediction of rice blast disease severity is divided into four classes: 0, 1, 2, and 3. Data imbalance is the most challenging problem in multi-class classification. This study has efficiently handled imbalanced data using k-means SMOTE and SMOTE oversampling techniques to balance training and testing data. Finally, cross-location and cross-year models are developed using a linear support vector machine and predict the severity of rice blast disease to the classes 0, 1, 2, 3, respectively. Cross-year and cross-location models are cross-validated using five-fold cross-validation.

Assessing rice blast disease severity through hyperspectral remote sensing

Remote sensing is being increasingly used in stress management in different agricultural practices. It is useful for real time analysis for crop stress which is not possible for visual observation alone. Rice blast caused by fungus Pyricularia Oryzae is a serious constrain in rice production in India. There is hardly any basic information available for spectral characteristics of rice blast disease for its real-time detection and management. Present study is to characterize spectral reflectance of blast affected rice in order to identify the sensitive spectral range. Disease severity of 10 different genotypes of rice was graded 0 to 9 based on the extent of host organ covered by symptom or lesion. Result shows that severely infected plant (score 9) have higher reflectance at visible region and lower reflectance at NIR region. Change in the reflectance for the infected plant as compare to the healthy plant was more pronounced in the VNIR, 550 to 760 nm and 1140 and 1300 nm having correlation coefficient above 0.6. The study of change in the reflectance with the change in wavelength (1st derivative) revealed that VNIR region have high correlation with the disease severity. Maximum rate of change value at red edge position (REP) is called as red edge value (REV) which has good relation with disease severity levels. Amplitude of the red edge peak decreases with the increase in severity levels. Amplitude of score 0 and 9 was 0.00929 and 0.002301, respectively for upland land condition whereas the amplitude of the score 0 and 9 was 0.010421 and 0.00193, respectively for upland land rice. This study identifies that VNIR and red edge region are sensitive for detecting rice blast, which could be utilized to aerial or satellite based monitoring blast affected rice cropping region.

Spatial distribution and identification of potential risk regions to rice blast disease in different rice ecosystems of Karnataka.

Rice is a globally important crop and highly vulnerable to rice blast disease (RBD). We studied the spatial distribution of RBD by considering the 2-year exploratory data from 120 sampling sites over varied rice ecosystems of Karnataka, India. Point pattern and surface interpolation analyses were performed to identify the spatial distribution of RBD. The spatial clusters of RBD were generated by spatial autocorrelation and Ripley’s K function. Further, inverse distance weighting (IDW), ordinary kriging (OK), and indicator kriging (IK) approaches were utilized to generate spatial maps by predicting the values at unvisited locations using neighboring observations. Hierarchical cluster analysis using the average linkage method identified two main clusters of RBD severity. From the Local Moran’s I, most of the districts were clustered together (at I > 0), except the coastal and interior districts (at I < 0). Positive spatial dependency was observed in the Coastal, Hilly, Bhadra, and Upper Krishna Project ecosystems (p > 0.05), while Tungabhadra and Kaveri ecosystem districts were clustered together at p < 0.05. From the kriging, Hilly ecosystem, middle and southern parts of Karnataka were found vulnerable to RBD. This is the first intensive study in India on understanding the spatial distribution of RBD using geostatistical approaches, and the findings from this study help in setting up ecosystem-specific management strategies against RBD.

An extension of mathematical model for severity of rice blast disease

&lt;abstract&gt;&lt;p&gt;This paper aims to extend the spore dispersal model to the Healthy-Latent-Infectious-Removed (HLIR) epidemic model for assessing the severity of rice blast disease. The model was solved by the Finite Difference Method (FDM). The results of the model were compared to data from the Prachinburi Rice Research Center (PRRC) on the severity of rice blast disease. Because of a small error, the comparison results showed good agreement between the PRRC data and the simulation by looking at the value of Willmott's index of agreement ($ d $). The first bed $ d $ was 0.7166, while the second bed $ d $ was 0.6421, indicating the model's performance. Furthermore, the optimal parameter, the fraction of spores deposited on the crop, was determined to be 0.173 and 0.016 for beds 1 and 2, respectively. The model can simulate and analyze rice blast outbreaks for educational purposes in future preparedness planning.&lt;/p&gt;&lt;/abstract&gt;

Foliar Spray of Silicon Enhances Resistance against Pyricularia oryzae by Triggering Phytoalexin Responds in Aerobic Rice

Rice blast (caused by Pyricularia oryzae) is the most devastative disease threatening sustainability rice production. The role of silicon as a foliar application in biochemical defence involvement towards P. oryzae infection in aerobic rice remains unclear. The goal of this study was to explore the effectiveness of silicon (Si) as a foliar spray in triggering phytoalexin synthesis to increase resistance against P. oryzae infection on two aerobic rice cultivars MR219-4 (partially resistant to rice blast) and MARDI Aerob 1 (resistant). Three Si sources: calcium silicate, silica oxide and sodium metasilicate were tested at 3, 6, and 9 mg/L against P. oryzae infection. Foliar application of calcium silicate at 9 mg/L significantly reduced rice blast disease severity to 0.11% (MARDI Aerob 1) and 3.30% (MR219-4). In vitro screenings of phytoalexins (sakuranetin and momilactone A) against P. oryzae revealed that sakuranetin is more prominent to inhibit P. oryzae in both solid and liquid media. The expression of sakuranetin was further quantified from Si-mediated rice seedlings after challenge inoculated with P. oryzae. High-Performance Liquid Chromatography (HPLC) revealed that sakuranetin in both Si-mediated rice seedlings inoculated with P. oryzae significantly increased at 2nd DAI with 0.13 mg/mL in MARDI Aerob 1 and 0.48 mg/mL in MR219-4 compared with control (without Si foliar application). These results emphasized calcium silicate as foliar spray augmented resistance to P. oryzae infection by prolonging sakuranetin accumulation as one of the mechanisms that strengthening the rice plant health besides physiological barrier mechanism in the aerobic rice.

Model of rice blast disease under tropical climate conditions

The Pyricularia oryzae is a fungus that leads to rice blast disease (RBD) in rice cultivar (Khao Dawk Mali 105), which grew in Thailand. The weather condition is one of the factors that affect plant and disease development. A Mathematical model is a useful tool for studying the dynamics and severity of plant disease. In this research, the severity of RBDs is simulated under environmental conditions, temperature, humidity, and dryness, in different parts of Thailand. The adopted model is developed to investigate the pathogen's life cycle together with the disease development in the paddy field. The result illustrates that temperature, the climatic factor , is the highest affected by the disease severity. In addition, the disease severity is high when it is low temperature and high humidity. On the other hand, the low severity also tends to be inverse in high severity. Moreover, the model can capture the outbreak period and predict the spatial distribution of the disease severity under climate conditions.

Efficacy of berberine in controlling foliar rice diseases

Berberine showed in vitro remarkable antifungal activity against rice pathogens including Bipolaris oryzae, Curvularia lunata, Pyricularia oryzae and Rhizoctonia solani with MIC values of 125 μg/mL. It showed potent preventative and curative activities in suppression of brown leaf spot disease of a susceptible Oryza sativa var. KDML 105 under greenhouse conditions. Berberine at 5 mg/mL showed effective brown leaf spot disease suppression in rice when applied before pathogen inoculation. It also showed higher fungicidal activity in suppression of brown leaf spot disease in plants aged 30 and 60 days than did difenoconazole and mancozeb when applied after pathogen inoculation. Moreover, berberine at 10 mg/mL significantly (P < 0.05) reduced the percentage of rice blast disease severity by 49.81%, which was similar to the action of difenoconazole and mancozeb when applied twice under field conditions. However, it showed low fungicidal activity against dirty particle disease, a complex disease of rice, under field conditions when compared with synthetic fungicides. These results indicated that berberine is a promising bioactive compound which may be developed as a lead compound in a new fungicide to control brown leaf spot and blast diseases of rice.

Nitrogen supply reduces the earthworm-silicon control on rice blast disease in a Ferralsol

Revealing belowground-aboveground relationships (BAR) is essential to drive ecological processes to address agriculture dysfunctions, especially in the management of aboveground plant diseases. Earthworms are one of the most important soil organisms involved in BAR, and silicon (Si) has been identified as a crucial element regulating aboveground plant health. How earthworm-Si interactions induce BAR in poor- and rich-nutrient soil contexts is still poorly understood, despite a growing interest in agricultural sustainability. We investigated the potential of BAR induced by the earthworm-silicon interaction to control the severity of rice blast disease in a Ferralsol in Madagascar, with or without NPK fertilization. We conducted a greenhouse microcosm experiment in which we manipulated the presence of the endogeic earthworm Pontoscolex corethrurus and the fungus Pyricularia oryzae in a Ferralsol supplied or not with Si and fertilized with macronutrients (nitrogen, phosphorus and potassium, i.e., NPK). After eight weeks of growth, plant biomass, nutrition and disease severity were measured. Our results validated the hypothesis that a dual treatment of earthworm inoculation and Si fertilization in a nutrient-poor tropical soil confers a higher tolerance of rainfed rice to P. oryzae, in comparison with treatments with only earthworms or Si, providing the optimal agronomic balance between a gain in biomass (and nutrition) and a reduction in disease severity. The supply of macronutrients altered this positive BAR by favouring the phenomenon of N-induced susceptibility. The aboveground plant C:N ratio of 15 is a threshold below which any increase in N per C unit likely enhances blast disease. The role of belowground interactions to counteract agricultural dysfunctions is supported by our study. To accomplish ecological intensification and provision of ecosystem services such as disease regulation, our findings recommend replacing excessive use of macronutrient fertilizer with sustained agricultural practices promoting the development of earthworm populations, such as organic matter inputs, superficial or no tillage, and the use of cover crops or conservation agriculture.

Pseudomonas Cyclic Lipopeptides Suppress the Rice Blast Fungus Magnaporthe oryzae by Induced Resistance and Direct Antagonism.

Beneficial Pseudomonas spp. produce an array of antimicrobial secondary metabolites such as cyclic lipopeptides (CLPs). We investigated the capacity of CLP-producing Pseudomonas strains and their crude CLP extracts to control rice blast caused by Magnaporthe oryzae, both in a direct manner and via induced systemic resistance (ISR). In planta biocontrol assays showed that lokisin-, white line inducing principle (WLIP)-, entolysin- and N3-producing strains successfully induced resistance to M. oryzae VT5M1. Furthermore, crude extracts of lokisin, WLIP and entolysin gave similar ISR results when tested in planta. In contrast, a xantholysin-producing strain and crude extracts of N3, xantholysin and orfamide did not induce resistance against the rice blast disease. The role of WLIP in triggering ISR was further confirmed by using WLIP-deficient mutants. The severity of rice blast disease was significantly reduced when M. oryzae spores were pre-treated with crude extracts of N3, lokisin, WLIP, entolysin or orfamide prior to inoculation. In vitro microscopic assays further revealed the capacity of crude N3, lokisin, WLIP, entolysin, xantholysin and orfamide to significantly inhibit appressoria formation by M. oryzae. In addition, the lokisin and WLIP biosynthetic gene clusters in the producing strains are described. In short, our study demonstrates the biological activity of structurally diverse CLPs in the control of the rice blast disease caused by M. oryzae. Furthermore, we provide insight into the non-ribosomal peptide synthetase genes encoding the WLIP and lokisin biosynthetic machineries.

Reduction of initial occurrence of rice blast (Pyricularia oryzae) inocula on seeds by microbial and hot water seed treatments

Rice blast disease resulting from infected rice seed can be avoided by using treated seeds. Seed treatment using chemical fungicide has many limitations such as development of resistance to pathogens, damage to the natural environment and the health of farmers and consumers. Such limitations have raised the need for alternative non-chemical seed treatment methods such as antagonist microbial agents and hot water. Laboratory and the screen house experiments were carried out with the aim of evaluating the efficacy of 'Trichoderma asperellum', 'Bacillus subtilis' and hot water (50 degreesC/15 min) seed treatments against rice blast disease inocula on rice seeds. The results showed that, seeds treated with microbial agents ('T. asperellum', 'B. subtilis') and hot water reduced the percentage of infected rice seeds by 4.3 to 52.7% relative to non-treated seeds. The germination percent and seedling vigour index increased from 12.3 % to 17.1 % . Rice seeds treated with 'B. subtilis' reduced the incidence and severity of rice blast disease from 10% to 72.4 %. Seed treatment using 'B. subtilis' followed by 'T. asperellum' were the best in reducing the number of infected seeds and rice blast disease incidence and severity on rice seedlings. Therefore, the use of these microbial agents has a potential for effective management of rice blast disease.

Pemodelan Keparahan Penyakit Blas pada Tanaman Padi di Kabupaten Subang

Modelling on Rice Blast Disease Severity in Subang DistrictBlast disease (Pyricularia oryzae) is a major diseases of rice in Indonesia. Research related to modelling of blast disease severity is limited. Therefore, this study aimed to design a statistical model on rice blast disease infestation on the rice paddy and to asses a correlation between the disease severity and infected seed level. The models were constructed based on multiple linier regression analyses. The study was conducted by observing the disease severity, collecting information about cultivation technique and weather conditions. The result of regression analysis showed severity modeling on influencing factors is Y = -67.17 + 5.51X1 – 10.54X2 + 13.26X3 + 8.51X4 + 2.29X5 + 1.32X6 + 8.47X7 + 0.31X8 + 4.53X9 (p-value &lt;0.0001, R2 = 0.85). Nitrogen application and plant ages had significant effect on disease severity. The addition of N fertilizer increased the severity of blast disease by 8.47%. Increasing the daily life of plants increases the disease severity by 0.31%. The correlation (r) of pathogen infection after harvesting was strongly influenced by infection before planting with correlation value of 0.78. This means that the severity of seed disease after harvesting is influenced by 78% infection of pathogenic seed before planting. The result of regression analysis showed Y = 5.98 + 2.41X (p-value = 0.0076, R2 = 0.61). An increase of 1% pathogens carried by seed before planting will be increasing disease severity by 2.41% after harvesting. The results of this study can be used as a reference in preparing preventive control measure and reduce the risk of pathogen carried by seeds that act as a source of initial inoculum.

Numerical solution of the differential equation for simulation of the rice blast disease

Rice blast disease is one of the diseases that causes damage to rice yield in Thailand. This research aims to simulate the severity of rice blast disease using the EPIRICE model for Khao Dawk Mali 105 that caused by Pyricularia oryzae in Prachin Buri, Thailand, and evaluate the simulation results by comparing with field collection data using root mean square error (RMSE). The epidemiological model consists of a system of ordinary differential equations (ODEs) that describes the dynamic of rice leaf disease. The Euler’s method is used to approximate the solutions of the ODEs. According to the RMSE, the simulation results were good agreement with the field collection data. Therefore, the numerical methods can be the technical tool for solving the severity of rice blast disease.Keywords: EPIRICE model, Khao Dawk Mali 105, Numerical Solution, Pyicularia oryzae, Rice blast disease

Induction of Resistance in Rice Against Magnaporthe Oryzae by Culture Filtrates of Biscogniauxia sp. O821

AbstractThe fungal strain O821 of Biscogniauxia sp. was isolated from wild mushrooms collected in Japan. Here, we demonstrate that a 24‐h pretreatment of rice leaves with an ethyl acetate extract of a culture filtrate from strain O821 (O821‐ECF) reduced the severity of rice blast disease caused by infection with Magnaporthe oryzae. To investigate possible mechanisms of this effect, we examined defence responses in the leaves. O821‐ECF treatment elicited the production of hydrogen peroxide (H2O2) and increased transcription of the PBZ1 gene. A time course analysis of H2O2 production indicated an increase with time after O821‐ECF treatment. Expression of the PBZ1 gene similarly peaked at 24 h after O821‐ECF treatment. However, no accumulation of salicylic acid (SA) was observed at 24 h after O821‐ECF treatment. These results suggest that SA‐independent resistance to rice blast is induced by O821‐ECF. Studies of O821‐ECF may contribute to the development of new plant activators for plant diseases such as rice blast disease.

Development of Microbial-Fortified Rice Straw Compost to Improve Plant Growth, Productivity, Soil Health, and Rice Blast Disease Management of Aerobic Rice

In aerobic rice cultivation systems, compost mulching and incorporation are important to rehabilitate the soil. Microbial-fortified compost is increasingly accepted as a safe approach in agro-waste management to recycling of crop residuals in agriculture soil and also to promote growth and suppress disease. This study aims to examine the stability and viability of the selected plant growth-promoting microorganisms (PGPM) in rice straw compost (RSC) over incubation period and its bio-efficacy in promoting rice (Oryza sativa) plant growth, productivity, soil health, and controlling of Pyricularia oryzae in aerobic cultivation conditions. Six selected PGPM: Pseudomonas aeruginosa (UPMP1), Corynebacterium agropyri (UPMP7), Enterobacter gergoviae (UPMP9), Bacillus amyloliquefaciens (UPMS3), Trichoderma harzianum (UPMT1), and Trichoderma virens (UPMT2) were used as a consortium of microbial inoculants to develop the microbial-fortified rice straw compost (MRSC). The MRSC was incorporated into mineral soil used for aerobic rice cultivation and its bio-efficacy was evaluated at harvest. The viability of Trichoderma spp. found stabilized at 6.78–6.00 log cfu/g and declined for all the bacterial isolates. At harvest, soil amended with MRSC significantly increased in plant height, leaf area index, 1000 grain weight, and productivity. The MRSC amended plots had significant low in rice blast disease severity with area under disease progress curve (AUDCP) of 748.22 unit/square, as compared to control (1782.67 unit/square). The physicochemical and microbiological properties of soil amended with MRSC were improved at harvest. The application of MRSC has potential to improve plant growth, productivity, rice blast disease management, and soil health of rice under aerobic cultivation systems.

Effects of acivicin on growth, mycotoxin production and virulence of phytopathogenic fungi.

Acivicin is an inhibitor of γ-glutamyl transpeptidase and glutamine amidotransferase. When grown on a synthetic minimal agar medium, acivicin strongly inhibited the growth of Magnaporthe oryzae and Alternaria brassicicola, and to a lesser extent, Botrytis cinerea. However, only partial or marginal growth inhibition was observed with regard to Fusarium sporotrichioides and Fusarium graminearum. The growth retardation caused by acivicin was significantly alleviated by cultivating the fungus on a nutrient-rich medium. The inhibition of M. oryzae growth caused by 1 μmol l(-1) of acivicin on minimal agar medium was subdued by the addition of specific single amino acids, including His, a branched-chain amino acid (Leu, Ile or Val), an aromatic amino acid (Trp, Tyr or Phe), Met or Gln, at a concentration of 0·4 mmol l(-1). Trichothecene production by F. graminearum in trichothecene-inducing liquid medium was reduced significantly in the presence of acivicin despite its inability to inhibit growth in the trichothecene-inducing liquid medium. Foliar application of conidia in the presence of acivicin reduced the severity of rice blast disease caused by M. oryzae. These results suggest the usefulness of this modified amino acid natural product to mitigate agricultural problems caused by some phytopathogenic fungi. Significance and impact of the study: Fusarium head blight or scab disease and rice blast, caused by Fusarium graminearum and Magnaporthe oryzae, respectively, are major diseases of cereal crops that cause a significant loss of yield and deterioration in the quality of the grain. The present study investigated the effects of acivicin, a glutamine amino acid analog, on the physiology of various phytopathogenic fungi. Application of acivicin to a fungal culture and conidial suspension reduced mycotoxin production by the wheat scab fungus and the severity of rice blast, respectively. These results suggest the possibility that acivicin may serve as a lead compound to develop agricultural chemicals for the control of some plant diseases.

Bio-efficacy of microbial-fortified rice straw compost on rice blast disease severity, growth and yield of aerobic rice

The bio-efficacy of microbial-fortified rice straw compost was evaluated for plant growth promotion, resistance induction and yield increment with Pyricularia oryzae challenged inoculation at 14, 56 and 80 days after sowing (DAS) on rice variety M4 under greenhouse conditions. Soil treatments included control (laterite soil alone), rice straw compost and rice straw compost fortified with four plant growth-promoting rhizobacteria: Pseudomonas aeruginosa (UPMP1), Corynebacterium agropyri (UPMP7), Enterobacter gergoviae (UPMP9), Bacillus amyloliquefaciens (UPMS3) and two plant growth-promoting fungi: Trichoderma harzianum (UPMT1) and Trichoderma virens (UPMT2). Soil amended with microbial-fortified rice straw compost significantly increased plant growth and productivity. Rice yield was highly correlated to productive tiller number (r = 0.96), leaf area index (LAI) (r = 0.96) and plant height (r = 0.97) for P. oryzae inoculation at 14 DAS. However, 1000 grain weight (r = 0.96), area under disease progress curve (AUDPC) (r = −0.62) and infected panicle (r = −0.59) were highly correlated to rice yield with P. oryzae inoculation at 80 DAS. Low productivity was expected with P. oryzae infection at the later growth stage. This was due to increase in panicle blast that caused deterioration of grain quality and resulting in severe yield loss (30.99 %) as compared to early infection at 14 DAS in soil amended with microbial-fortified rice straw compost. Disease development and yield loss data with different P. oryzae inoculation timings is important for disease management in rice under aerobic cultivation system.

Effect of a Multiline of Rice Cultivar Sasanishiki and Its Isogenic Lines on Suppressing Rice Blast Disease.

The effect of the multiline consisting of a rice cultivar, Sasanishiki, and its isogenic lines on the rice blast disease caused by Pyricularia oryzae Cavara was investigated under natural conditions. The blast disease severity and the percent diseased plants in the mixtures were less than that observed in the single line plantings. The blast disease occurrence in the mixture of compatible and incompatible lines was less than that of the compatible lines mixture. Moreover, even in the compatible lines mixture, the rice blast disease severity was depressed significantly. It became apparent that a reduced inoculum density effect and a barrier effect for infection depressed the blast disease, and it was assumed that an induced resistance operated to suppress the blast disease in the Sasanishiki's multiline. Furthermore, the feasibility of using the Sasanishiki multiline of ten isogenic lines with different true resistances was effective for the control of blast diseases.