Bio-Solarization as an Integrated Approach in the Management of Rice Blast

In recent years, rice demand has been on the increase while its production is decreasing due to biotic and abiotic stresses. Rice blast caused by Magnaporthe oryzae remains the major biotic factor affecting smallholder rice farmers. This fungal disease cause 60-100% yield losses in rice production, thus leading to food insecurity especially in Sub-Saharan Africa. Currently, the disease is managed through prophylactic application of synthetic fungicides which are not environmentally friendly. Thus, the use of biopesticide may offer a sustainable management strategy. In this study, the efficacy of Trichoderma hamatum was assessed against rice blast disease through seeds-priming, roots dipping and foliar sprayed at 5ml/20L of water in the greenhouse. Data was collected on disease incidence and severity, tiller number, height, grains yield and dry root and shoot weights. The disease was scored on a scale of 0-10. Log transformed data was analyzed using one-way analysis of variance in GenStat 14th edition. The treatments means were separated using Tukeys studentized test. The results of this study indicates that the mode of application of T. hamatum had significant influence on rice blast severity on the leaves and panicles (P<0.006) and (P<0.001) respectively. The lowest blast severity was recorded in the foliar sprayed rice plants, compared to seeds-priming, roots dipping and control. The difference in leaf blast severity was significant between the foliar sprayed to that of seeds-priming, roots dipping and control. This study also revealed that the mode of delivery of T. hamatum was important in influencing grains yield of the rice (P<0.001). The highest grains yield was recorded in the foliar sprayed rice. Therefore, this study suggests that there is a potential in the use of foliar spray of T. hamatum in the management of rice blast and the enhancement grains yield of rice.

To better understand RNA-binding proteins in rice, a comprehensive investigation was conducted on the RRM1 gene family of rice. It encompassed genome-wide identification and exploration of its role in rice blast resistance. The physicochemical properties of the rice OsRRM1 gene family were analyzed. There genes were also analyzed for their conserved domains, motifs, location information, gene structure, phylogenetic trees, collinearity, and cis-acting elements. Furthermore, alterations in the expression patterns of selected OsRRM1 genes were assessed using quantitative real-time PCR (qRT-PCR). A total of 212 members of the OsRRM1 gene family were identified, which were dispersed across 12 chromosomes. These genes all exhibit multiple exons and introns, all of which encompass the conserved RRM1 domain and share analogous motifs. This observation suggests a high degree of conservation within the encoded sequence domain of these genes. Phylogenetic analysis revealed the existence of five subfamilies within the OsRRM1 gene family. Furthermore, investigation of the promoter region identified cis-regulatory elements that are involved in nucleic acid binding and interaction with multiple transcription factors. By employing GO and KEGG analyses, four RRM1 genes were tentatively identified as crucial contributors to plant immunity, while the RRM1 gene family was also found to have a significant involvement in the complex of alternative splicing. The qRT-PCR results revealed distinct temporal changes in the expression patterns of OsRRM1 genes following rice blast infection. Additionally, gene expression analysis indicates that the majority of OsRRM1 genes exhibited constitutive expressions. These findings enrich our understanding of the OsRRM1 gene family. They also provide a foundation for further research on immune mechanisms rice and the management of rice blast.

The rice blast incited byPyricularia oryzaecaused immense losses and left rice production in a predicament situation globally. Blast can be effectively controlled with synthetic fungicides. However, their indiscriminate use causes resistance among the pathogens coupled with environmental pollution issues. Exploitation of microbe‐based alternatives for the management of plant diseases diminishes public concerns on the ill effects of pesticide usage in crops. Under this scenario the present investigation was designed to envisage the potential rhizosphere microflora from native rhizosphere soil samples collected from rice growing regions of three different agro‐climatic zones of (North Telangana Zone, Central Telangana Zone and Southern Telangana Zone) for the sustainable management of rice blast in Telangana state. We observed varied level of antagonism againstPyricularia oryzaeunder in vitro conditions. Seeds treated with native effective rhizospheric microflora exhibited significantly higher seed vigour index ranging from 1940.7 to 2183.6 compared to control. Further, these effective rhizospheric microbes were identified through cultural and morphological characteristics as well as by the sequencing internal transcribed spacer (ITS) and 16S rRNA gene sequences analysis for bacteria and fungi asBacillus cereus,Bacillus xiamenensis,Bacillus subtilisandTrichoderma asperellumrespectively. Later, bio‐efficacy tests were carried out in the field during the 2 years of Kharif 2019 and 2021 by spraying the combinations of the antagonists in association with indigenous organic sources (Panchagavya, Beejamrutham and Vermiwash) and non‐chemical sources such as Butter milk and Neem oil on healthy rice plants to assess disease inhibition under natural conditions. Results obtained from present investigation on the field bio‐efficacy studies showed significant improvement in the seedling's growth with 83.36 cm plant height, 10.40 no of panicles with an average yield of 8583.33 kg ha−1, when compared to control during 2019 and 2021 with lower AUDPC and r value. Our findings indicate that the native rhizospheric microflora in association with indigenous organic sources can be used as potential alternative strategy for the management of rice blast in Telangana region of India. The knowledge gathered from the present study can be used to develop strategies for maintaining soil quality and crop conservation to increase crop productivity with less dependency on chemical approaches.

Rice blast disease is known as rice rotten neck, rice blight of seedlings, ryegrass blast and Johnson spot in different locations and is considered as the most destructive disease of rice in the world. It is caused by a filamentous, ascomycetous fungus Magnaporthe oryzae (syn. Pyricularia oryzae), which is polycyclic in nature and spreads by asexual spores (conidia). The infection spreads inside the host cell without causing visible symptoms in the early stage and above ground tissues of rice plants. The disease is reported in almost all the rice-growing seasons and an estimated yield loss is 10–30% of the total production. It has the ability to infect more than 50 species of grasses, including economically important crops like rice, wheat, barley and pearl millet. This disease is effectively managed by avoiding excessive nitrogen application which enhances the leaf area in per unit area which induces disease susceptibility. Moreover, balancing of the use and application of nitrogen in three split doses (50% N at basal, 25% N at tillering stage and 25% doses of N at panicle initiation stage) minimises the threat of blast diseases in standing crops. Foliar spray of systemic fungicide like tebuconazole 75 WG @ 500–750 g/ha, tricyclazole 75 WP @ 500 g/ha, metominostrobin 20 SC @ 500 mL/ha, or azoxystrobin 25 SC @ 500 mL/ha was highly effective with its protectivity and curative efficacy against the diseases when applied at boot growth and heading stage. This book chapter emphasises on blast pathogen, evolution, adaptation, pathogenesis and management of rice blast in the context of changing climate.

Management of rice blast (Pyricularia oryzae): implications of alternative hosts

Management of rice blast with modern combination fungicides against Magnaporthe oryzae

In this study, spatial analyses were conducted at three different scales to better understand the epidemiology of rice blast, a major rice disease caused by Magnaporthe oryzae. At the regional scale, across the major rice production regions in China, rice blast incidence was monitored on 101 dates at 193 stations from 10 June to 10 September during 2009 to 2014, and surveyed in 143 fields in September 2016; at the county scale, three surveys were done covering one to five counties in 2015 to 2016; and, at the field scale, blast was evaluated in six fields in 2015 to 2016. Spatial cluster and hot spot analyses were conducted in the geographic information system on the geographical pattern of the disease at regional scale, and geostatistical analysis was performed at all three scales. Cluster and hot spot analyses revealed that high-disease areas were clustered in mountainous areas in China. Geostatistical analyses detected spatial dependence of blast incidence with influence ranges of 399 to 1,080 km at regional scale and 5 to 10 m at field scale but not at county scale. The spatial patterns at different scales might be determined by inherent properties of rice blast and environmental driving forces, and findings from this study provide helpful information to sampling and management of rice blast.

Rice blast (Pyriculariaoryzae Cavara) is one of the most devastating diseases affecting the rice crop in across the world. Systemic fungicides are used for the suppression of blast diseases caused by fungal pathogens. Propiconazole and Carbendazim are commercial chemical control products available in markets for the control of the fungal pathogen. An experiment was conducted to examine the effectiveness of systemic fungicide on suppression of rice blast incidence in farmers' field during wet seasons in 2016. The treatments consisted of the use of different levels of propiconazole and Carbendazim on ‘Rato Basmati’ a landrace rice variety. The experiments were arranged in a randomized complete block design with three replications. The disease was scored according to the standard scale developed by the International Rice Research Institute (IRRI). Disease severity and Area under Disease Progressive curve (AUDPC) was computed based on that scale score. Propiconazole and Carbendazim at different levels reduce disease development than no treatment (control). But its efficacy was not consistent. The magnitude of disease suppression by Propiconazole was high as compared to Carbendazim. The application of propiconazole at the rate of 1.5 ml effectively reduced disease severity and AUDPC at different dates. So propiconazole at the rate of 1.5 ml thrice at weekly intervals is effective to reduce the disease development

Rice blast, aused by Magnaporthe oryzae B.C.Couch, is considered as the main fungal disease in rice fields in Burkina Faso. This study aimed to assess the essential oils of Cymbopogon schoenanthus, Ocimum americanum, Ocimum gratissimum and Lippia multiflora on mycelial radial growth and inhibition rate of the fungus using the contact and fumigation methods. For each essential oil, six doses were used : T0 (0 µl/ml), T1 (0.1 µl/ml), T2 (0.6 µl/ml), T3 (1.2 µl/ml), T4 (1.8 µl/ml) and T5 (2.4 µl/ml). In both tests, two treatments of synthetic fungicides namely Tma (mancozeb) and Taz (azoxystrobin) at recommended doses of 6.67 µl/ml and 3.33 µl/ml respectively. The results showed that in the contact method, essential oils of L. multiflora, O. americanum,C. schoenanthus and O. gratissimum inhibited 100% (0 cm of diameter) the fungus mycelial radial growth at doses of T3 (1.2 µl/ml), T5 (2.4 µl/ml), T2 (0.6 µl/ml) and T2 (0.6 µl/ml) respectively. As for the fumigation method, oils of L. multiflora, O. americanum,C. schoenanthus and O. gratissimum inhibited mycelial radial growth of the fungus by 100% at doses of T2 (0.6 µl/ml), T5 (2.4 µl/ml), T4 (1.8 µl/ml) and T3 (1.2 µl/ml) respectively. Mancozeb and azoxystrobin treatments inhibited radial mycelial growth by 100% and 74.1% respectively. These essential oils can be used to control rice blast in the field. The use of these essential oils in rice blast management may also help to reduce environmental pollution caused by synthetic fungicides.”

Fungicides are the preferred rice blast (Pyricularia oryzae) control option by farmers. However, no fungicides are yet registered for this purpose in Australia. Hence, it is important to test the baseline sensitivity of P. oryzae isolates collected from blast-affected regions across northern Australia, which have not yet been exposed to the fungicides, as part of a resistance management strategy. Further, it is also important to investigate and compare effect of application timing of fungicides on conidial development, including germination and germ tube growth, and penetration on susceptible rice. The EC50 of a collection of fungicide-sensitive blast isolates were within the range of 0.02–2.02 and 0.06–1.91 mg L−1 for azoxystrobin and propiconazole, respectively. Azoxystrobin was shown to have greater inhibitory effect on conidial germination than propiconazole. In addition, for pre-inoculation application, only germ tubes in the presence of external nutrients continued to grow from 24 to 48 hpi. On susceptible seedlings, both fungicides completely controlled blast disease when applied the same day as inoculation. However, for pre- or post-inoculation application of fungicide, the extent of disease control was reduced, with azoxystrobin more efficacious than propiconazole. A stimulatory effect of both fungicides at low dose was observed on certain P. oryzae isolates. This is the first study to assess the baseline sensitivity of the P. oryzae population in Australia and the first to report a stimulatory effect of low azoxystrobin concentration on growth of P. oryzae. The study highlights, for the first time, the critical role of external nutrients in promoting germ tube growth under fungicide stress conditions. Lastly, it demonstrates the high degree of efficacy of the fungicides and their potential for future rice blast management in Australia.

Magnaporthe oryzae is the major pathogen of cultivated rice worldwide, which can cause substantial losses to rice production. Rice blast management is based predominantly on the application of fungicides; however, only a little is known about responses of pathogen populations to the most widely used fungicides. In this work, the baseline sensitivity of the Italian M. oryzae population to tricyclazole and azoxystrobin in terms of mycelium growth was determined, and the possible adaptation of the pathogen population after several years of repeated exposure to fungicide treatments was evaluated. All the analyzed strains demonstrated higher sensitivity and variability to azoxystrobin (concentration of fungicide causing 50% growth inhibition [ED50] = 0.063 mg liter-1) than to tricyclazole (99.289 mg liter-1). After comparing two additional populations collected from fields repeatedly treated with fungicides to the baseline, no decrease in sensitivity toward these fungicides was observed and no resistant strains were detected. The shift of the pathogen sensitivity toward these fungicides has not occurred, although we observed slightly increased variance associated with ED50 of azoxystrobin. Therefore, both azoxystrobin and tricyclazole can be used to manage rice blast in Italy but it will be important to continue monitoring M. oryzae population to early detect possible azoxystrobin resistance.

In Japan, simulation models of rice blast epidemics have been developed as a tool for disease forecasting services in the public domain since the early 1970s. Later, the government changed the policy on disease management and started to emphasize lesser dependency on fungicides. Consequently, the disease forecasting had to introduce the concept of integrated pest management (IPM). An idea was proposed to use a simulation model for blast forecasting as a decision support system (DSS) based on IPM strategy. However, it is difficult to determine economic injury level (EIL) and action threshold (AT) of blast disease based on objective evidences. Also, accuracy and precision of simulation models of natural systems is innately insufficient. These two issues challenge the usefulness of simulation models for contemporary rice blast management. However, only if the EIL are subjectively determined by the decision-makers, forecasting with a simulation model can play a major role for IPM program for rice blast disease. The next step should be large scale field trials to test the usefulness of this system. The results certainly become strong evidences to encourage introducing the system into rice blast management programs.

Rice blast, caused by the filamentous fungus Pyricularia oryzae, has long been one of the major threats to almost all rice-growing areas worldwide. Metconazole, 5-(4-chlorobenzyl)-2, 2-dimethyl-1-(1H-1, 2, 4-triazol-1-ylmethyl) cyclopentanol, is a lipophilic, highly active triazole fungicide that has been applied in the control of various fungal pathogens of crops (cereals, barley, wheat), such as the Fusarium and Alternaria species. However, the antifungal activity of metconazole against P. oryzae is unknown. In this study, metconazole exhibited broad spectrum antifungal activities against seven P. oryzae strains collected from rice paddy fields and the wild type strain P131. Scanning electron microscopic analysis and fluorescein diacetate staining assays revealed that metconazole treatment damaged the cell wall integrity, cell membrane permeability and even cell viability of P. oryzae, resulting in deformed and shrunken hyphae. The supplementation of metconazole in vitro increased fungal sensitivity to different stresses, such as sodium dodecyl sulfate, congo red, sodium chloride, sorbitol and oxidative stress (H2O2). Metconazole could inhibit key virulence processes of P. oryzae, including conidial germination, germ tube elongation and appressorium formation. Furthermore, this chemical prevented P. oryzae from infecting barley epidermal cells by disturbing appressorium penetration and subsequent invasive hyphae development. Pathogenicity assays indicated a reduction of over 75% in the length of blast lesions in both barley and rice leaves when 10 μg/mL of metconazole was applied. This study provides evidence to understand the antifungal effects of metconazole against P. oryzae and demonstrates its potential in rice blast management.

BackgroundWith its adapted microbial diversity, the phyllosphere contributes microbial metagenome to the plant holobiont and modulates a host of ecological functions. Phyllosphere microbiome (hereafter termed phyllomicrobiome) structure and the consequent ecological functions are vulnerable to a host of biotic (Genotypes) and abiotic factors (Environment) which is further compounded by agronomic transactions. However, the ecological forces driving the phyllomicrobiome assemblage and functions are among the most understudied aspects of plant biology. Despite the reports on the occurrence of diverse prokaryotic phyla such as Proteobacteria, Firmicutes, Bacteroides, and Actinobacteria in phyllosphere habitat, the functional characterization leading to their utilization for agricultural sustainability is not yet explored.Currently, the metabarcoding by Next-Generation-Sequencing (mNGS) technique is a widely practised strategy for microbiome investigations. However, the validation of mNGS annotations by culturomics methods is not integrated with the microbiome exploration program. In the present study, we combined the mNGS with culturomics to decipher the core functional phyllomicrobiome of rice genotypes varying for blast disease resistance planted in two agroclimatic zones in India. There is a growing consensus among the various stakeholder of rice farming for an ecofriendly method of disease management. Here, we proposed phyllomicrobiome assisted rice blast management as a novel strategy for rice farming in the future.ResultsThe tropical "Island Zone" displayed marginally more bacterial diversity than that of the temperate ‘Mountain Zone’ on the phyllosphere. Principal coordinate analysis indicated converging phyllomicrobiome profiles on rice genotypes sharing the same agroclimatic zone. Interestingly, the rice genotype grown in the contrasting zones displayed divergent phyllomicrobiomes suggestive of the role of environment on phyllomicrobiome assembly. The predominance of phyla such as Proteobacteria, Actinobacteria, and Firmicutes was observed in the phyllosphere irrespective of the genotypes and climatic zones. The core-microbiome analysis revealed an association of Acidovorax, Arthrobacter, Bacillus, Clavibacter, Clostridium, Cronobacter, Curtobacterium, Deinococcus, Erwinia, Exiguobacterium, Hymenobacter, Kineococcus, Klebsiella, Methylobacterium, Methylocella, Microbacterium, Nocardioides, Pantoea, Pedobacter, Pseudomonas, Salmonella, Serratia, Sphingomonas and Streptomyces on phyllosphere. The linear discriminant analysis (LDA) effect size (LEfSe) method revealed distinct bacterial genera in blast-resistant and susceptible genotypes, as well as mountain and island climate zones. SparCC based network analysis of phyllomicrobiome showed complex intra-microbial cooperative or competitive interactions on the rice genotypes. The culturomic validation of mNGS data confirmed the occurrence of Acinetobacter, Aureimonas, Curtobacterium, Enterobacter, Exiguobacterium, Microbacterium, Pantoea, Pseudomonas, and Sphingomonas in the phyllosphere. Strikingly, the contrasting agroclimatic zones showed genetically identical bacterial isolates suggestive of vertical microbiome transmission. The core-phyllobacterial communities showed secreted and volatile compound mediated antifungal activity on M. oryzae. Upon phyllobacterization (a term coined for spraying bacterial cells on the phyllosphere), Acinetobacter, Aureimonas, Pantoea, and Pseudomonas conferred immunocompetence against blast disease. Transcriptional analysis revealed activation of defense genes such as OsPR1.1, OsNPR1, OsPDF2.2, OsFMO, OsPAD4, OsCEBiP, and OsCERK1 in phyllobacterized rice seedlings.ConclusionsPCoA indicated the key role of agro-climatic zones to drive phyllomicrobiome assembly on the rice genotypes. The mNGS and culturomic methods showed Acinetobacter, Aureimonas, Curtobacterium, Enterobacter, Exiguobacterium, Microbacterium, Pantoea, Pseudomonas, and Sphingomonas as core phyllomicrobiome of rice. Genetically identical Pantoea intercepted on the phyllosphere from the well-separated agroclimatic zones is suggestive of vertical transmission of phyllomicrobiome. The phyllobacterization showed potential for blast disease suppression by direct antibiosis and defense elicitation. Identification of functional core-bacterial communities on the phyllosphere and their co-occurrence dynamics presents an opportunity to devise novel strategies for rice blast management through phyllomicrobiome reengineering in the future.Graphical abstract

Rice (Oryza sativa) plays a significant role in achieving global food security. However, it suffers from several biotic and abiotic stresses that seriously affect its production. Rice blast caused by hemibiotropic fungal pathogen Magnaporthe oryzae is one of the most widespread and devastating diseases of rice. The crop rice is vulnerable to this pathogen from seedlings to adult plant stages affecting leaves, nodes, collar, panicles and roots. This disease can be effectively managed through host resistance. Of the 100 blast resistance genes, identified and mapped in different genotypes of rice, 19 genes have been cloned and characterized at the molecular level. Most of these genes belong to nucleotide binding sites and leucine rich repeats. Besides more than 350 quantitative trait loci (QTLs) have also been identified in the rice genome. These blast resistance genes and QTLs have been successfully mobilized in the commercial cultivars by using standard plant breeding techniques and also by marker assisted backcross breeding. With the advent of latest molecular biology techniques and our understanding of the basic mechanisms of Magnaporthe-rice pathosystem, the strategies for broad-spectrum resistance to M. oryzae can be designed in future.