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The fresh and dried whole plant (CF and CD respectively) of Cympopogon citratus essential oils (EOs) and its fractions, were tested, for their antifungal activities against Bipolaris oryzae and Fusarium moniliforme; respectively responsible of brown spot and bakanae disease of rice (Oryzae sativa L). Their chemical compositions were obtained by GC-GC/MS analysis and correlated with their biological activities. All six collected EO fractions of C. citratus contain myrcene, limonene, α-gurjunene, neral and geranial, but in different proportions. Neral (45.64 - 79.00%) predominant in CD1, CD2, CDm, CFm, and geranial (18.79 - 45.64%) in CF1, CF2; were found as major components. A positive correlation between the biological activity and the predominant constituent (citral) content was not always apparent. Carvacrol acetate and farnesol (2E, 6Z) were found only in EO fractions from fresh plants (CF1, CF2, CFm), and have high antifungal activity against B. oryzae and F. moniliforme compared to that of fractions from dried plants (CD1, CD2, CDm). The EO fractions collected within the first 60 min starting from the moment the first drop of EO was dropped (CF1, CD1), were more active than the fractions collected after 61 min (CF2, CD2). Cedrol, hexahydrofarnesyl acetone, γ-decalactone, β-bisabolol, α-muurolol, cavacrol and β-eudesmol, were present in low amount in CF2 and CD2 and absent in CF1 and CD1. The results serve as benchmark for researchers/industries, in fast and better targeting bioactive compounds and identify plausible interactions that may exist between constituents of an essential oil for a given biological activity. [ABSTRACT FROM AUTHOR]

Conidial production is a critical factor in testing pathogenicity and studying the physiology and ecology of fungal pathogens. Therefore, selecting an appropriate condition and medium for consistent conidia production is essential. In this study, we investigated light conditions and suitable medium conditions using the slide culture method to establish optimal conditions for continuous spore acquisition of Bipolaris oryzae. Primarily, we observed conidial production using two B. oryzae isolates, CM23-042 and 23CM10, under two different light conditions: (1) consistent near-ultraviolet (NUV) with fluorescent light, and (2) a 12-hr shift of the NUV-dark cycle. Secondly, we examined conidial formation under seven different media on potato dextrose agar (PDA), V8-Juice agar, minimal medium (MM), sucrose-proline agar (SPA), rabbit food agar (RFA), rice bran agar (RBA), and rice leaf agar (RLA). Under consistent NUV light with fluorescent conditions, conidia were induced in both isolates, whereas conidia were not produced under other conditions after 7 days post-inoculation (dpi). Moreover, B. oryzae isolate CM23-042 produced the highest number of conidia in MM, while isolate 23CM10 yielded the highest number of conidia in PDA after 7 dpi. In summary, our data demonstrated that the consistent NUV light with fluorescent conditions were most conducive for conidia induction in B. oryzae. The selection of a medium for conidiation may vary depending on the B. oryzae isolates, but using MM and PDA or SPA and RFA medium could be effective for spore induction. These findings will contribute to improving conidiation according to the characteristics of collected isolates of B. oryzae.

Rice (Oryzae sativa L.) is one of the most important cereal crops on which an ever-increasing population is dependent for food globally. However, constraints associated with infectious diseases, notably brown spot transmitted by seed and wind reduced its production and productivity. This study was conducted to characterize Bipolaris oryzae isolates morphologically in Fogera plain, Amhara region of Ethiopia. Twenty-nine B. oryzae isolates were collected from Dera, Fogera, and Libokemkem districts and characterized morphologically at the Ambo Agricultural Research Center plant pathology laboratory. These isolates were grouped into nine categories on their colony morphology and growth pattern. About 34.48% of the isolates showed black with fluffy growth pattern, while 68.96% of the conidia shape were slightly curved. Moreover, 58.62% of 29 isolates was initially hyaline. Fast, moderate and slow mycelial growth habits were also observed in 29 isolates, from 3.07 to 15.49 μm in length and from 1.00 to 4.27 μm in breadth conidia size and from 1.52 × 109 to 1.80 × 1010/ml sporulation rates. Therefore, knowing such characteristics is crucial and it needs to identify the pathogen inherent genetic characteristics of the above isolates for fruitful management recommendations.

Abstract Rice brown spot is an important disease of rice worldwide that inflicts substantial yield losses. The antimicrobial potential of methanol, acetone and dimethyl sulfoxide (DMSO) extracts of different medicinal plants, viz., Syzygium aromaticum, Saussurea costus, Acorus calamus, Bergenia ciliate, Geranium pratense, Mentha longifolia, Inula racemosa, Podophyllum hexandrum, Heracleum candicans and Picrorhiza kurroa, against the brown spot pathogen Bipolaris oryzae in vitro was evaluated via mycelial growth inhibition and spore germination inhibition assays. Among the plant extracts tested, 100% mycelial inhibition was observed for the methanol extract of Syzygium aromaticum at all three concentrations (2000 ppm, 3000 ppm and 4000 ppm), followed by the methanol extract of Inula racemosa (90.33%) at 4000 ppm. A maximum conidial germination inhibition of 83.54% was exhibited by the Heracleum candicans leaf extract. Phytochemical profiling of Syzygium aromaticum and Inula racemosa through liquid chromatography and mass spectrometry (HR-LCMS) revealed the presence of several compounds, such as eugenol, ursolic acid, quercetin, chlorogenic acid, and noscapine. A molecular docking approach was used to identify key inhibitory molecules against B. oryzae. Among the compounds detected in S. aromaticum and Inula racemosa, ursolic acid and noscapine were found to have the greatest binding affinity for the Big Mitogen Activated Protein Kinase (BMK-1) enzyme present in B. oryzae. In conclusion, S. aromaticum and Inula racemosa are potent compounds that could serve as lead compounds for drug discovery in the future.

Brown spot (BS) disease causes significant losses to rice productivity. In this study, a roving survey in the Karnataka state of India revealed a wider distribution of BS with a percent disease index range of 20.56–50.74. From the symptomatic geo-distinct samples, pure cultures of 63 isolates were obtained. Based on the conidial morphology, 63 isolates were identified as Bipolaris oryzae (Bo) (n = 40), Curvularia lunata (Cl) (n = 15), and Exserohilum rostratum (Er) (n = 08). The taxonomic identity was further confirmed via ITS-sequencing. A pathogenicity assay on a BS-susceptible rice cultivar GNV-05–01 confirmed the pathogenicity of all three pathogens, which induces typical BS disease on test plants. Further, on PDA media, all isolates of three pathogens showed significant cultural diversity for mycelial color, colony type, and sporulation. We further studied the in-planta distribution of three pathogens on a randomly collected 600 BS spots from 10 different rice fields, which indicated that 77.83%, 17.33%, and 4.83% of the typical BS were produced by Bo, Cl, and Er, respectively. The ITS region was sequenced for selected 9, 7, and 3 isolates of Bo, Cl, and Er, respectively, and analyzed for their nucleotide and haplotype diversity, and phylogenetic relationships. A phylogenetic study identified the unique clustering patterns, and haplotyping indicated 3, 4, and 6 haplotypes. Tajima's D (D) test showed several rare alleles in the ITS regions. This is the first comprehensive study reporting the three fungal pathogens causing BS of rice and it is useful for re-designing the screening protocol for the host plant resistance breeding program. [ABSTRACT FROM AUTHOR]

Rice brown spot is an important disease of rice worldwide that inflicts substantial yield losses. The antimicrobial potential of methanol, acetone and dimethyl sulfoxide (DMSO) extracts of different medicinal plants, viz., Syzygium aromaticum, Saussurea costus, Acorus calamus, Bergenia ciliate, Geranium pratense, Mentha longifolia, Inula racemosa, Podophyllum hexandrum, Heracleum candicans and Picrorhiza kurroa, against the brown spot pathogen Bipolaris oryzae in vitro was evaluated via mycelial growth inhibition and spore germination inhibition assays. Among the plant extracts tested, 100% mycelial inhibition was observed for the methanol extract of Syzygium aromaticum at all three concentrations (2000 ppm, 3000 ppm and 4000 ppm), followed by the methanol extract of Inula racemosa (90.33%) at 4000 ppm. A maximum conidial germination inhibition of 83.54% was exhibited by the Heracleum candicans leaf extract. Phytochemical profiling of Syzygium aromaticum and Inula racemosa through liquid chromatography and mass spectrometry (HR-LCMS) revealed the presence of several compounds, such as eugenol, ursolic acid, quercetin, chlorogenic acid, and noscapine. A molecular docking approach was used to identify key inhibitory molecules against B. oryzae. Among the compounds detected in S. aromaticum and Inula racemosa, ursolic acid and noscapine were found to have the greatest binding affinity for the Big Mitogen Activated Protein Kinase (BMK-1) enzyme present in B. oryzae. In conclusion, S. aromaticum and Inula racemosa are potent compounds that could serve as lead compounds for drug discovery in the future. [ABSTRACT FROM AUTHOR]

Many fungicides can control brown spot, caused by Bipolaris oryzae in rice (Oryza sativa L.), although searching for beneficial microorganisms for biocontrol will improve sustainable integrated pest management. The aim of this investigation was the selection of natural suppressors of the brown spot disease in rice. We performed biochemical (E1), molecular antagonism (E2) and severity suppression (E3) studies under laboratory and greenhouse conditions. The E1, E2 and E3 assays were performed with 21 isolates. The experimental design was completely randomized with three replicates. E1 characterized all 21 isolates for the production of extracellular enzymes, siderophores, biofilm, indole‐3‐acetic acid (IAA) and phosphate solubilization. E2 was conducted to test the in vitro antagonism between the 21 isolates and B. oryzae, and E3 was conducted under greenhouse conditions, where seeds of the rice cultivars BRS‐Primavera and Esmeralda were sown in plastic trays containing 3 kg of fertilized soil. After 45 days, rice leaves were sprayed and inoculated with a mixed suspension of bacterial cells (1 × 108 CFU) and B. oryzae. All of the 21 bacterial isolates produced lipase, N‐fixation, siderophore, IAA, biofilm and solubilized phosphorus. Bacillus cereus, Priestia megaterium, Stenotrophomonas nitritireducens, Serratia marcescens and Serratia nematodiphila reduced radial colony growth of B. oryzae and suppressed brown spot severity by up to 90%. This indicates the potential of these isolates for biocontrol of brown spot in rice as a component of rice disease management. [ABSTRACT FROM AUTHOR]

The ability of microorganisms to promote plant growth and mitigate abiotic and biotic stresses makes them an interesting tool for sustainable agriculture. Numerous studies aim to identify new, promising bacteria isolates. Traditional culture-based methods, which focus on selecting microorganisms with plant-growth-promoting traits, such as hormone production, nutrient solubilization, and antifungal properties, are widely used. This study aims to investigate the role of plant-growth-promoting properties in bacteria-mediated stress mitigation and the suitability of traditional culture-based methods as a screening tool for the identification of beneficial bacteria. To this end, we tested three endophytic Bacillus isolates, which have previously been shown to affect tolerance against iron toxicity in lowland rice, (a) for their effect on the resistance against brown spot disease, and (b) for plant-growth-promoting traits using common culture-based methods. Both B. pumilus isolates inhibited fungal growth in vitro and reduced brown spot disease in two of three rice cultivars in planta, although they tested negative for all plant-growth-promoting traits. While B. megaterium was negative for ACC deaminase activity and nutrient solubilization, it exhibited auxin production. Nevertheless, B. megaterium did not suppress brown spot disease in any of the three rice cultivars. This study shows that bacteria do not necessarily have to possess classical plant-growth-promoting properties in order to be beneficial to plants, and it emphasizes the limitation of common culture-based methods in effectively identifying beneficial bacteria. Moreover, our results highlight the significance of the interaction between bacteria and plant cultivars in determining the beneficial effects of Bacillus spp. on plants under biotic or abiotic stresses. [ABSTRACT FROM AUTHOR]

Dirty panicle disease is one of the most important diseases that can cause yield losses in rice production. Despite the severity of the disease, the molecular basis of resistance to the pathogen is poorly understood. Using QTL-seq with an F2 population, we identified three genomic regions on chromosomes 1, 9, and 10, namely qDP1, qDP9, and qDP10. These regions are significantly associated with resistance to dirty panicle disease caused by two fungal pathogens, Bioplaris oryzae and Cirvularia lunata. qDP1 was significantly associated only with resistance to B. oryzae, whereas qDP9 and qDP10 were significantly associated with both B. oryzae and C. lunata. We also developed KASP markers for each QTL detected and validated them in the F2 population. The markers were able to explain phenotypic variation in a range of 5.87–15.20%. Twelve potential candidate genes with annotated functions as resistance-related genes were proposed. These candidate genes include those encoding RLK, MATE, WAK, NBS-LRR, subtilisin-like protease, and ankyrin repeat proteins. The results of this study provide insights into the genetic mechanism of dirty panicles in rice and will be useful for future breeding programs for dirty panicle resistance. This is the first report of QTLs associated with resistance to dirty panicle disease in rice. [ABSTRACT FROM AUTHOR]

Bipolaris oryzae, fungal pathogen causing rice brown spot disease, exerts a significant economic impact by reducing rice yield and quality. The costs associated with the management of this destructive pathogen, including fungicide applications and other preventive measures, increase the cost of cultivation and pave the way for the economic burden faced by rice farmers and the broader agricultural industry. Taking this into consideration, 32 spermosphere bacteria were isolated from various rice landraces and challenged against the virulent isolate of Bipolaris oryzae (OM977033) under in vitro conditions. Among them, six strains of spermosphere bacteria from different rice seeds exhibited notable inhibitory effects on the tested pathogen. SPKKM 4 isolated from Navara, SPKKM 2 from Mappillaisamba, SPKKM 5 from Navara black, SPKKM 18 from Kavuni, SPKKM 9 from Mallikar and SPKKM 32 from ADT 44 rice seeds exhibited pronounced inhibition of Bipolaris oryzae mycelial growth. Furthermore, seedling vigor assessments revealed the remarkable growth-promoting potential of SPKKM 5, SPKKM 4, and SPKKM 2 among the tested bacterial strains. Molecular characterization confirmed their identities as Bacillus subtilis (OQ073461), Acinetobacter schindleri (OK342196) and Acidovorax spp. (OP522279), respectively. Subsequent pot culture experiments demonstrated that Bacillus subtilis (SPKKM 5) applied at 10 ml kg-1 as seed treatment and foliar spray (0.5%) at flowering and 15 days later, resulted in a remarkable 65.86% reduction in disease incidence compared to the control. [ABSTRACT FROM AUTHOR]

Chitin is a well-known elicitor of disease resistance and its recognition by plants is crucial to perceive fungal infections. Chitin can induce both a local immune response and a systemic disease resistance when provided as a supplement in soils. Unlike local immune responses, it is poorly explored how chitin-induced systemic disease resistance is developed. In this study, we report the systemic induction of disease resistance against the fungal pathogen Bipolaris oryzae by chitin supplementation of soils in rice. The transcriptome analysis uncovered genes related to cell-wall biogenesis, cytokinin signaling, regulation of phosphorylation, and defence priming in the development of chitin-induced systemic response. Alterations of cell-wall composition were observed in leaves of rice plants grown in chitin-supplemented soils, and the disease resistance against B. oryzae was increased in rice leaves treated with a cellulose biosynthesis inhibitor. The disruption of genes for lysin motif (LysM)-containing chitin receptors, OsCERK1 (Chitin elicitor receptor kinase 1) and OsCEBiP (Chitin elicitor-binding protein), compromised chitin-induced systemic disease resistance against B. oryzae and differential expression of chitin-induced genes found in wild-type rice plants. These findings suggest that chitin-induced systemic disease resistance in rice is caused by a perturbation of cell-wall biogenesis in leaves through long-distance signalling after local recognition of chitins by OsCERK1 and OsCEBiP. [ABSTRACT FROM AUTHOR]

Brown spot disease of rice caused by Bipolaris oryzae results in severe yield losses. A high-quality genome was assembled using Nanopore sequencing data, resulting in a 36-Mb nuclear genome with 19 contigs and a mitogenome. This assembly provides valuable genetic resources for investigations of rice- B. oryzae interactions., Competing Interests: The authors declare no conflict of interest.

Chitin is a well-known elicitor of disease resistance and its recognition by plants is crucial to perceive fungal infections. Chitin can induce both a local immune response and a systemic disease resistance when provided as a supplement in soils. Unlike local immune responses, it is poorly explored how chitin-induced systemic disease resistance is developed. In this study, we report the systemic induction of disease resistance against the fungal pathogen Bipolaris oryzae by chitin supplementation of soils in rice. The transcriptome analysis uncovered genes related to cell-wall biogenesis, cytokinin signaling, regulation of phosphorylation, and defence priming in the development of chitin-induced systemic response. Alterations of cell-wall composition were observed in leaves of rice plants grown in chitin-supplemented soils, and the disease resistance against B. oryzae was increased in rice leaves treated with a cellulose biosynthesis inhibitor. The disruption of genes for lysin motif (LysM)-containing chitin receptors, OsCERK1 (Chitin elicitor receptor kinase 1) and OsCEBiP (Chitin elicitor-binding protein), compromised chitin-induced systemic disease resistance against B. oryzae and differential expression of chitin-induced genes found in wild-type rice plants. These findings suggest that chitin-induced systemic disease resistance in rice is caused by a perturbation of cell-wall biogenesis in leaves through long-distance signalling after local recognition of chitins by OsCERK1 and OsCEBiP.

The ability of microorganisms to promote plant growth and mitigate abiotic and biotic stresses makes them an interesting tool for sustainable agriculture. Numerous studies aim to identify new, promising bacteria isolates. Traditional culture-based methods, which focus on selecting microorganisms with plant-growth-promoting traits, such as hormone production, nutrient solubilization, and antifungal properties, are widely used. This study aims to investigate the role of plant-growth-promoting properties in bacteria-mediated stress mitigation and the suitability of traditional culture-based methods as a screening tool for the identification of beneficial bacteria. To this end, we tested three endophytic Bacillus isolates, which have previously been shown to affect tolerance against iron toxicity in lowland rice, (a) for their effect on the resistance against brown spot disease, and (b) for plant-growth-promoting traits using common culture-based methods. Both B. pumilus isolates inhibited fungal growth in vitro and reduced brown spot disease in two of three rice cultivars in planta, although they tested negative for all plant-growth-promoting traits. While B. megaterium was negative for ACC deaminase activity and nutrient solubilization, it exhibited auxin production. Nevertheless, B. megaterium did not suppress brown spot disease in any of the three rice cultivars. This study shows that bacteria do not necessarily have to possess classical plant-growth-promoting properties in order to be beneficial to plants, and it emphasizes the limitation of common culture-based methods in effectively identifying beneficial bacteria. Moreover, our results highlight the significance of the interaction between bacteria and plant cultivars in determining the beneficial effects of Bacillus spp. on plants under biotic or abiotic stresses.

Global rice production is seriously affected by many abiotic and biotic factors. Among the aggressive rice pathogens, Xanthomonas oryzae pv. oryzae (X. o. pv. oryzae), Bipolaris oryzae (B. oryzae) and Sphaerulina oryzina (S. oryzina) cause bacterial leaf blight, brown leaf spot and narrow brown leaf spot diseases, respectively. The objective of this study was to evaluate the efficacy of biogenic zinc oxide nanoparticles (ZnO NPs) as antimicrobial agent to control rice pathogens. This is the first report of antifungal activity evaluation of ZnO NPs against B. oryzae and S. oryzina. A pre-characterized bacterial strain Escherichia sp. SINT7 was bio-prospected for synthesis of green ZnO NPs. The NPs were confirmed by a characteristic peak measured at 360.96 nm through UV–Vis spectroscopy. Further, the NPs were characterized to elucidate the surface capping molecules, crystallite structure and morphology by various spectroscopic and imaging techniques, which confirmed the spherical shape of NPs with size ranging from 13.07 to 22.25 nm. In vitro studies against X. o. pv. oryzae pathogen depicted the substantial antibacterial activity (up to 25.7 mm inhibition zone at 20 μg/ml NPs concentration). Similarly, ZnO NPs reduced the mycelial growth of B. oryzae and S. oryzina up to 72.68 and 95.78%, respectively at 50 μg/ml concentration on potato dextrose agar plates, while the mycelial biomass reduction was found to be 64.66 and 68. 49% for B. oryzae and S. oryzina, respectively on potato dextrose broth media as compared to control without the addition of NPs. The green ZnO NPs also significantly reduced the fungal spore germination and a disintegration of fungal hyphae for both fungal strains was observed under the microscope as a result of NPs treatment. Hence, it was concluded that biologically synthesized ZnO NPs are potential antimicrobials and could be compared in greenhouse pathogenicity assays with commercial pesticides to control rice pathogens. [ABSTRACT FROM AUTHOR]

The impact of atmospheric glow discharge plasma and plasma activated water on reducing rice seed-borne brown spot disease was investigated. It has been shown that the generation of reactive oxygen and nitrogen species by plasma containing electrons, positive or negative ions, and neutral species has antimicrobial activity. In this study, four plasmas were used for seed treatment viz., O2-air glow discharge plasma for 90 s, 120 s, air-plasma activated water for 9 and 12 min. Control (without treatment) and chemical treatment were used in order to compare the treatment effect. The plasma treatments used for this study showed a promising positive effect on seed germination and plant growth, and reduction of brown spot severity in the field. Among the plasmas, O2-air glow discharge plasma for 90s significantly increased seed germination (94.67%) compared to control (84.0%). Conidial suspension of Bipolaris oryzae treated with O2-air glow discharge plasma for 90 s and air-plasma activated water for 9 min successfully reduced the conidial germination ability of Bipolaris oryzae on Potato Dextrose Agar (PDA). The brown spot incidence and severity were significantly reduced in the plot which received seed treatment with O2-air glow discharge plasma for 90s and air-plasma activated water for 9 min. Interestingly, the same treatment remarkably enhances the plant growth parameters and yield of BRRI dhan28 compared to control treatment. [Fundam Appl Agric 2021; 6(2.000): 107-118]

Brown leaf spot (BLS), a disease caused by the fungus Bipolaris oryzae (teleomorph: Cochliobolus miyabianus), is a major economic concern in rice-growing regions around the world including Pakistan, but it has gotten little attention in Pakistan. All well-known Basmati rice cultivars are affected by BLS. During 2020-21, surveys were conducted in nine rice-growing districts of Punjab province, Pakistan, from various fields of rice, infected samples were collected. BLS was found in all of Punjab's surveyed districts. According to the findings, eighty-five rice fields were surveyed, and 81 were found to be infected with BLS. Gujranwala has the highest BLS incidence (51%), Hafzabad (50%), and Narowal (47%). The highest severity rate was 75% in Super rice in district Gujranwala at Nathu Siwiya road, while the lowest was 5% in basmati rice in Gujrat. Based on morphological characterization, the pathogen was identified as B. oryzae. The findings showed that BLS has been present in rice-producing regions of Pakistan, particularly in the Basmati region of Punjab, for many years. To reduce inoculum levels and yield losses, resistant Basmati cultivars must be introduced. [ABSTRACT FROM AUTHOR]

Rice brown leaf spot disease is one of the most devastating fungal diseases that affect rice plants and reduces the yield across the globe. In the present study, twenty isolates from different rice-growing districts in Tamil Nadu by tissue segment approach was isolated from disease-infected leaves and a purified. The isolates were identified at the genus level using ITS primers, which resulted in an amplicon size of a 550 bp. With the use of species-specific primers of BF and BR the isolate was confirmed as B. oryzae. Gene-specific primers were designed using Primer 3 plus software for the Glycoside hydrolase family 13 protein, which is a highly conserved gene in B. oryzae. All isolates were sequenced using gene-specific primers, and phylogenetic tree analysis was used to investigate the isolate's diversity. The results revealed considerable variance among the B. oryzae collected from different locations of Tamil Nadu with other B .oryzae isolates retrieved from the NCBI database. The isolates were phenotypically validated using morphological and cultural features. [ABSTRACT FROM AUTHOR]

Dhungana, A., Puri, C., Shah, K., Yogi, S., Dhakal, D.P., Acharya, B., and Shrestha, J. 2020. Screening rice genotypes for brown spot disease resistance. Tunisian Journal of Plant Protection 15 (2): 29-39.

Brown spot, caused by Bipolaris oryzae, is a devastating disease of rice which can cause yield loss in most rice-growing regions of the world. Breeding for disease resistance is the preferred strategy of managing brown spot. Hence, identification and subsequent development of disease resistance in rice genotypes are crucial. The field resistance of 95 rice genotypes to brown spot was evaluated under water and fertilizer stress during 2017 and 2018. Partial resistance was assessed through reaction type (disease rating) and epidemiological parameters estimates i.e. final brown spot index, area under disease progress curve and apparent infection rate. Disease rating, brown spot index, and area under disease progress curve detected differences in the responses of rice genotypes to disease under field condition, which could be used to study brown spot resistance. Among the genotypes tested, 22 genotypes were resistant to moderately resistant (23.16%) while majority were moderately susceptible to susceptible (76.84%). A significant correlation between leaf angle and area under disease progress curve indicated positive influence of leaf erectness on severity of brown spot disease. Results showed that leaf infection did not significantly affect the number of filled grains per panicle or hundred seed weight, but caused yield decline by decreasing the number of productive tillers. Nevertheless, the infection of rice genotypes from flowering to ripening stages decreased the number of filled grains per panicle and grain weight. The resistant genotypes identified in this study can be exploited for future rice breeding programs to develop promising resistant lines in management of the brown spot disease.

Rice brown spot (BS), caused by Bipolaris oryzae, causes yield loss and deterioration of grain quality. Using single-nucleotide polymorphism (SNP) markers, we conducted quantitative trait locus (QTL) analysis of BS resistance in backcross inbred lines (BILs) from a cross between an American rice cultivar, 'Dawn' (resistant), and 'Koshihikari' (susceptible). Four QTLs for BS resistance were detected in a three-year field evaluation, and 'Dawn' contributed the resistance alleles at all QTLs. The QTL with the greatest effect, qBSR6-kd, explained 15.1% to 20.3% of the total phenotypic variation. Although disease score and days to heading (DTH) were negatively correlated in all three years, qBSR6-kd was located near a QTL for DTH at which the 'Dawn' allele promoted heading. Another BS resistance QTL (qBSR3.1-kd) was unlinked to the QTLs for DTH. Therefore, these two QTLs are likely to be useful for breeding BS-resistant varieties without delaying heading. The other two BS resistance QTLs (qBSR3.2-kd and qBSR7-kd) were located near DTH QTLs at which the 'Dawn' alleles delayed heading. The QTLs reported here will be good candidates for developing BS-resistant cultivars. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the pathogenicity of Bipolaris oryzae, the causal agent of brown spot disease on Egyptian rice cultivars. Sample of rice were collected from 10 cultivars namely (Sakha 101, Sakha 104, Sakha 106, Giza 176, Giza 177, Giza 178, Giza 182, Egyptian hybrid and Egyptian Yasmin). Fungal genera were recovered from the rice samples. These fungi were identified as (Curvularia lunata, Asprgillus niger, Asprgillus flavus, Penicillium sp., Trichoderma, Alternaria alternata, Bipolaris oryzae, Fusarium verticillioides, Fusarium chlamydosporum, Rhizopus oryzae, Curvularia tuberculate, Bipolaris hawaiiensis, Cephaliophora tropica and Negrospora sp.). Out of the fourteen fungi, B. oryzae was characterized as one of the highest frequently exists fungus. Ten isolates of B. oryzae were investigated in terms of spore dimension, number of septa of conidia, linear growth and culture color. These ten B. oryzae isolates were used in the pathogenicity test on five commercial rice cultivars (Sakha 108, Sakha super 300, Giza 177, Giza 182 and Egyptian hybrid. The disease severity was assessed 7days after inoculation, 21-days-old rice plants. The most aggressive B. oryzae isolates were B.o10, B.o7, B.o9 and B.o8. On the other hand, the lowest aggressive once were B.o2, and B.o1. Screening of the B. oryzae isolates on the commercial rice cultivars in the rice cultivation area in Egypt could help develop prediction plane of brown spot disease, ultimately, facilitate the most proper decision for rice cultivars to be cultivated. [ABSTRACT FROM AUTHOR]

Brown leaf spot (BLS) (caused by Bipolaris oryzae) is among the most important disease affecting rice production in Punjab and in other regions in the Pakistan. Contact old fungicides have been used extensively to manage the diseases, especially BLS. Unfortunately, heavy reliance on use of fungicides with a single mode of action has induced the development of the contract resistant isolates of Bipolaris oryzae in the Pakistan. All the fungicide treatments were effective in reducing BLS incidence compared to the untreated control. The result of in vitro study depicted that among ten fungicides, Nanok (4.68mm) exhibited minimum fungus colony growth as compared to Evito (6.98), Electus Ultra (11.08), Nativo (10.87), Top Guard (12.6), Zandar (13.85), Bloom (17.54), Kasumin (20.43), Meishile (25.08) and Novice (30.91mm) respectively as compared to control (61.05) and best selected two systemic fungicides further evaluated in greenhouse and field condition. Result expressed that the combination of both fungicides Nanok+evito application showed minimum disease incidence (12.39%, 16.72%) as compared to Evito (16.11,23.22) and Nanok (23.05,30.05) respectively as compared to control (46,63.16) in green house and field experiments respectively. Interaction between treatments and concentration (TxC) represented that Nanok expressed maximum disease incidence at 0.5% (34), 1% (30.33) and 1.5% (25.83), followed by Evito (26.83,24,18.83) as compared to their combination Nanok+evito which showed the minimum disease incidence (19,17.16,14) with respectto control. [ABSTRACT FROM AUTHOR]

Brown leaf spot (BLS), Bipolaris oryzae is one of the emerging threats to the rice crop. Its infection caused deficiency of minerals contents in rice crop. Therefore, current study was designed to determine the variations of ionic contents in rice crop after the attack of BLS disease. The leaf samples of resistant rice varieties (Kissan Basmati, Chenab Basmati, IRRI-6) and susceptible varieties (Basmati-2000, Basmati-515, KSK-133) were analyzed, and the significant alterations (p ≤ 0.05) in the ionic contents were noted across treatments, types (un-inoculated and inoculated), groups (susceptible and resistant) and varieties of rice due to the infection of the pathogen. Nested structure analysis of variance revealed a significant difference in ionic status (N, P, K, Na, Ca, Cu, Fe, and Zn) of rice leaves. Resistant type of plants expressed 1.28% and 0.54% while susceptible type showed 1.22% and 0.43% difference in concentrations of N and K respectively. Moreover, resistant type expressed 7379.23, 2229.47, 5.02, 222.68, 28.94 and 662.29 ppm; while, susceptible type showed 7025.38, 1895.02, 4.15, 177.95, 22.17 and 520.71 ppm difference in concentrations of P, Na, Cu, Fe, Zn and Ca, respectively. It was accomplished that resistant variety stored ionic contents at higher concentrations than susceptible. The higher ionic contents concentration in resistant rice plants build up the physiological and biochemical processes of the rice plant, which help to avoid the spread of the pathogen. [ABSTRACT FROM AUTHOR]

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The nursery resistance of 95 rice genotypes to brown spot (BS) was evaluated under water stress and irrigated conditions during 2017 and 2018. Disease assessment was done by calculating the final brown spot index, area under the disease progress curve and apparent infection rate. Susceptible genotypes demonstrated high disease indices at both the hydrological treatments in comparison to resistant genotypes. Water shortage at the seedling stage caused an increasing rate of disease severity in rice genotypes; however, the responses varied among genotype. These findings suggest that the evaluation of resistance to brown spot disease could be done under water stress conditions. Among genotypes tested, 13 genotypes, i.e. Gharib-Siyah-Reihani, Ghashangeh, Gerdeh, Shahpasand, Neda, Sange-Tarom, Hasani, Dasht, Gohar, Kanto 51, Khazar, Koohsar and Mohammadi-Chaparsar exhibited seedling resistance to brown spot disease at both hydrological conditions which could be recommended for cultivation and further breeding utilization to develop promising resistant lines in management of the brown spot disease. [ABSTRACT FROM AUTHOR]

This research took place at the Provincial Plant Sanitation Laboratory, in Camaguey, Cuba, between September 2013 and September 2015. The in vitro compatibility and antagonistic capacity of Trichoderma harzianum Rifai (strain A-34) on rice pathogens (Bipolaris oryzae Breda de Haan, Sarocladium oryzae (Sawada) w., Gams and D. Hawksworth and Magnaporthe grisea (Hebert Barr), was determined against pesticides used on rice. Assessment using traditional methods of microbiological isolation of mycelial growth, sporulation and conidial germination of the antagonist, to determine if the action mechanisms (antibiosis, competence, parasitism) against fungal pathogens, was made between 24 and 216 hours of application. A bifactorial design in dual culture was used for statistical analysis, along with scales for determination of microbial antagonistic capacity. Active ingredients tebuconazol + procloraz, trifloxistrobin+ ciproconazole, and epoxiconazole + kresoxim-methyl, affected mycelial growth of the antagonist. Moreover, the antagonist against active ingredients carbendazim, copper oxychloride, azoxystrobin and tebuconazo + triadimenol showed mycelial growth, sporulation and pathogen interaction, affecting their growth by means of coiling, penetration, granulation, and cell lysis, between 96 and 216 hours.

Brown spot disease (Bipolarisoryzae) is increasing threat to global food security in the world as well as the most damaging disease of rice crop in Pakistan. In September 2017, a field survey was conducted in four rice-growing districts of Punjab namely (Faisalabad, Hafizabad, Sheikhupura and Lahore) and diseased samples were collected from different fields of rice showing disease symptoms. The results showed that Ninety-seven fields of rice were surveyed and 62 were found infected with disease. Disease prevalence was highest in district Sheikhupura 84%, followed by Lahore, Hafizabadand, Faisalabad with 80%, 60% and 53% respectively. The risk of disease incidence was highest in district Sheikhupura and Lahore82% in Super Basmati, 74% in KSK-282 followed by Faisalabad and Hafizabad71% in Super basmati, 60% in Super rice respectively. The severity rate was the highest in district Lahore at KotPindiDass 88%in Super rice, but the minimum was observed atShamke road 46% in PK 386. It is concluded that, the disease incidence and severity level of B. oryzae was higher in fields of district Sheikhupura in Punjab, Pakistan. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is a biomass candidate crop which has been improved for yield, but disease resistance development has largely been ignored. Bipolaris oryzae (Breda de Haan) Shoemaker can cause Bipolaris seed rot, reducing seedling establishment, and Bipolaris leaf spot, reducing biomass yield. In order to initiate a breeding program, heritability based on half-sib progenies of the disease resistance were conducted in 47 half-sib progenies of lowland 'Kanlow' and upland 'Cave-in-Rock'. Test crosses of progenies from resistant and susceptible parents in upland 'Shelter' and Cave-in-Rock were conducted to determine genetic control of resistance to Bipolaris leaf spot. To breed for resistance to two diseases, two cycles of recurrent phenotypic selection were done separately in Shelter and Cave-in-Rock at 10% selection intensity. As a result, resistance to Bipolaris seed rot showed moderate to high heritability (0.33 ± 0.16 to 0.83 ± 0.09) in both individual- and half-sib-based computations, reflecting actual genetic gain (44.5–125.3%) from two cycles of selections. However, resistance to Bipolaris leaf spot showed non-significant heritability (0.02 ± 0.06 to 0.19 ± 0.19) and non-significant progress of selection for the trait. Results from test crosses suggested that the resistance was not controlled by R genes but possibly was quantitatively inherited by many alleles with small effects. Such a difference in the gains resulted in non-significant correlation between two resistances. Due to high progress in selection resistance to Bipolaris seed rot, the screening method for resistance can be integrated to existing breeding programs. • Resistance to Bipolaris seed rot has moderate to high heritability resulting in high genetic gain from the selection. • Resistance to Bipolaris leaf spot has low or non-significant heritability resulting in no improvement from the selection. • Resistance to Bipolaris leaf spot should be controlled by multiple minor effect alleles. • There is no correlation between two disease resistances. [ABSTRACT FROM AUTHOR]

This research took place at the Provincial Plant Sanitation Laboratory, in Camaguey, Cuba, between September 2013 and September 2015. The in vitro compatibility and antagonistic capacity of Trichoderma harzianum Rifai (strain A-34) on rice pathogens (Bipolaris oryzae Breda de Haan, Sarocladium oryzae (Sawada) w., Gams and D. Hawksworth and Magnaporthe grisea (Hebert Barr), was determined against pesticides used on rice. Assessment using traditional methods of microbiological isolation of mycelial growth, sporulation and conidial germination of the antagonist, to determine if the action mechanisms (antibiosis, competence, parasitism) against fungal pathogens, was made between 24 and 216 hours of application. A bifactorial design in dual culture was used for statistical analysis, along with scales for determination of microbial antagonistic capacity. Active ingredients tebuconazol + procloraz, trifloxistrobin+ ciproconazole, and epoxiconazole + kresoxim-methyl, affected mycelial growth of the antagonist. Moreover, the antagonist against active ingredients carbendazim, copper oxychloride, azoxystrobin and tebuconazo + triadimenol showed mycelial growth, sporulation and pathogen interaction, affecting their growth by means of coiling, penetration, granulation, and cell lysis, between 96 and 216 hours.

Resumen La investigación se realizó en el Laboratorio Provincial de Sanidad Vegetal en Camagüey, en la etapa comprendida de septiembre de 2013 a septiembre de 2015, en condiciones in vitro donde se determinó la compatibilidad y capacidad antagónica frente a pesticidas usados en el arroz, de Trichoderma harzianum Rifai cepa A-34 sobre los patógenos del arroz (Bipolaris oryzae Breda de Haan, Saracladium oryzae (Sawada) w. Gams & D.Hawksworth y Magnaporthe grisea (Hebert) Barr). Las evaluaciones mediante métodos tradicionales de aislamiento microbiológico del crecimiento micelial, la esporulación y la germinación conidial del antagonista para determinar si ejerce los mecanismos de acción de antibiosis, competencia, y parasitismo ante los patógenos fúngicos se efectuaron a partir desde las 24 hasta las 216 horas empleando. Para el análisis estadístico se empleó un diseño bifactorial en el cultivo dual, además de las escalas para la determinación de la capacidad antagónica de los microorganismos. Los ingredientes activos tebuconazol + procloraz, trifloxistrobin+ ciproconazol, y epoxiconazol + kresoxim- metil, afectaron el crecimiento micelial del antagonista, por otra parte el antagonista frente a los ingredientes activos carbendazim, oxicloruro de cobre, azoxistrobina y tebuconazol + triadimenol tuvo crecimiento micelial, esporulación e interacción con los patógenos afectándose el crecimiento de los mismos a través de los mecanismos de acción de enrollamiento, penetración, granulación , y lisis celular desde las 96 hasta las 216 horas. Trichoderma harzianum Rifai compatibility with fungicides and its effect on three fungal plant rice pathogens. ABSTRACT The research was conducted at the Provincial Laboratory of Plant Protection in Camagüey, in the fall period September 2013 to September 2015, under in vitro conditions where compatibility and antagonistic capacity was determined against used in rice pesticides, Trichoderma harzianum Rifai strain A-34 on rice pathogens (Bipolaris oryzae Breda de Haan, Saracladium oryzae (Sawada) w. Gams & D.Hawksworth and Magnaporthe grisea (Hebert) Barr). Evaluations by traditional methods of microbiological isolation of mycelial growth, sporulation and conidial germination of the antagonist to determine whether to exercise the mechanisms of action of antibiosis, competition and parasitism against fungal pathogens were made from from 24 up to 216 hours. For statistical analysis, a two-factor design was used in the dual culture, plus scales for determining the ability of microorganisms antagonistic. The ingredients tebuconazole active + prochloraz, trifloxystrobin + cyproconazole, epoxiconazole + kresoxim- methyl, affected mycelial growth of the antagonist on the other hand the antagonist against the active ingredients carbendazim, copper oxychloride, azoxystrobin and tebuconazole + triadimenol had mycelial growth, sporulation and interaction with pathogens thereby affecting the growth of the same through the winding mechanisms of action, penetration, granulating, and cell lysis from 96 to 216 hours.

This work was developed at Agriculture Microbiology laboratory in the Agriculture Faculty at Universidad Central “Martha Abreu” de Las Villas, with the aim to evaluate the influence of incubation time of Trichoderma harzianum Rifai on antifungal activity of its culture filtrates against Bipolaris oryzae. Flask with Czapek broth was used for growing T. harzianum, then one disc of mycelium were incubated during 20 and 30 days at 28±1ºC and dark. Trichoderma harzianum (strain A-34) was submited to filtration process, and comparison were done among concentration of 0%, 25%, 50%, 75%, 100% (v/v). Major inhibition porcentaje were observed in concentrations of 75% y 100% both at 20 and 30 days of incubation. At 20 day the inhibition porcentaje was greater in comparsison with 30 days.

ABSTRACT: The occurrence of leaf spots in irrigated rice can reduce the yield and compromise the quality of the grain. However it is unknown the economic damage threshold (EDT) that these spots cause the yield of crop. The objective of this study was to obtain damage functions for models of critical, to relate damage by simultaneous occurrence of blast, brown spot and scald spot with grain yield harvests in 2011/12 and 2012/2013, in Rio do Oeste, Santa Catarina State, Brazil. Gradient of diseases intensity was generated by number of applications and fungicides rates. Design was a randomized block with four replications and six treatments consisting of mixing fungicide applications of triazole (difenoconazole) and strobilurin (azoxystrobin). In 2011/12 and 2012/13 growing season were made two and three tests respectively with the same experiment. Before each application it was determined the incidence and severity of fungal diseases. The critical point models were obtained by linear regression between grain yield and incidence (I) and severity (S). In 2011/12 the functions were not significant at the beginning of tillering and 2012/2013 harvest resulted in R=13.404-92.98I and R=10.685-3.804S. Respectively in each harvest resulted in tillering (R=9.141-103.6I; R=7.605-1.538 and R=8.864-73.91I; R=7.202-77S), panicle initiation (R=9.432-188.5I; R=7.,038-1.466S and R=10.176-87.33I; R=8.258-533.55S), booting (R=7.044-71.78I; R=6.881-1.296S and R=9.993-71.74I; R=8.846-763.83S), flowering (R=7.447-82.29I; R=8.731-1.398S and R=8.347-54.36I; R=7.338-681.52S) and milky grain (R=10.143-80.5I; R=7.522-1.402S and R=8.661-60.063I; R=9.754-1.465S). The generated functions allow getting the damage coefficient for use in the calculation of EDT in multiple pathossystem leaf spots in irrigated rice.

The inducible metabolites in rice leaves treated with 1 mM jasmonic acid (JA) were analyzed using HPLC. We detected an increase in the levels of two compounds, 1 and 2. Based on the comparison with mass spectra and chromatographic behavior with authentic compounds, 1 and 2 were identified as 13-oxooctadeca-9,11-dienoic acid (13-KODE) and 9-oxooctadeca-10,12- dienoic acid (9-KODE), respectively, which have not been detected in rice to date. The accumulation of these compounds was also induced by an infection by Bipolaris oryzae. Treatment of rice leaves with KODEs induced the accumulation of defensive secondary metabolites, sakuranetin, naringenin, and serotonin, suggesting that KODEs may play a role in the elicitation of defense responses. The compounds that have an á, â-unsaturated carbonyl group similar to KODEs did not reproduce the response of accumulation of defensive secondary metabolites, suggesting that additional structural factors such as long hydrophobic carbon chain are needed to elicit defense responses. [ABSTRACT FROM AUTHOR]

Bipolaris oryzae is a phytopathogenic fungus causing a brown spot disease in rice, and produces substance that strongly perturbs motility and membrane integrities of boar spermatozoa. The substance was isolated from the liquid culture of the fungal strain using extraction and a multi-step semi-preparative HPLC procedures. Based on the results of mass spectrometric and 2D NMR techniques, the bioactive molecule was identified as ophiobolin A, a previously described sesterterpene-type compound. The purified ophiobolin A exhibited strong motility inhibition and viability reduction on boar spermatozoa. Furthermore, it damaged the sperm mitochondria significantly at sublethal concentration by the dissipation of transmembrane potential in the mitochondrial inner membrane, while the plasma membrane permeability barrier remained intact. The study demonstrated that the cytotoxicity of ophiobolin A toward somatic cell lines is higher by 1–2 orders of magnitude compared to other mitochondriotoxic mycotoxins, and towards sperm cells unique by replacing the progressive motility by shivering tail beating at low exposure concentration.

Copyright of BIOAGRO is the property of Revista BIOAGRO and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aspergillus flavus, Bipolaris oryzae and Fusarium semitectum are fungi that infect rice crop both in field and storage. Seed health testing is conducted in order to prevent or to minimize risks caused by seed-borne pathogens. One of potential technology which can be developed as detection method is fiber optic fluorescence spectroscopy. The research aimed to develop an alternative detection method more rapid, accurate, and simple for seed-borne fungal pathogen based on secondary metabolites by using fiber optic spectroscopy fluorescence. This research covered: preparation of pure isolates of A. flavus, B. oryzae, and F. semitectum; calibration of fiber optic fluorescence spectroscopy and fungal secondary metabolite analysis by Py-GC-MS; and detection of A. flavus, B. oryzae and F. semitectum on rice seed. The data were analyzed by Spectrasuite Ocean Optic software. Fiber optic fluorescence spectroscopy was able to detect fluorescence emission of fungal metabolites after rice seed were incubated for 24 hours. Each fungus produced specific secondary metabolite when exposed to violet or ultraviolet light which has specific fluorescence emission. A. flavus produced aflatoxin B1 at 440 nm, B. oryzae produced ophiobolin A at 534 nm, and F.semitectum produced beauvericin at 510 nm. [ABSTRACT FROM AUTHOR]

In the present study, the effect of red light on the infection behavior of Bipolaris oryzae on rice leaves and the effects of chemical inhibitors and spore germination fluid (SGF) of B. oryzae on red-light-induced resistance against brown spot disease were investigated. Red light irradiation and natural light did not differ significantly with respect to their effect on spore germination and appressorium formation of B. oryzae 24 h after inoculation. However, formation of infection hyphae was significantly inhibited under red light compared to that under natural light. Pretreatment with the photosynthetic inhibitor 3-(3,4-dichorophenyl)-1,1-dimethylurea (DCMU) or with the aromatic amino acid inhibitor N-(phosphonomethyl) glycine (glyphosate) for 24 h inhibited the development of resistance in rice leaves. To elucidate the elicitor(s) produced during the B. oryzae-rice plant interaction, the effect of SGF prepared in the absence (A-SGF) or presence (P-SGF) of rice leaves on red-light-induced resistance was investigated. When rice plants were pretreated with A-SGF or P-SGF for 24 h, P-SGF had elicitor activity under red light, but not under natural light or with A-SGF. These results suggest that germinating spore of B. oryzae produced an elicitor(s) under red light conditions in a host-dependent manner. In conclusion, we hypothesize that an unidentified elicitor(s) produced at an early stage of fungal infection during the B. oryzae-rice interaction contributes to the inhibition of cell death in rice leaves under red light and enhances resistance-related tryptophan and phenylpropanoid pathways. [ABSTRACT FROM AUTHOR]

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Brown spot of paddy caused by Bipolaris oryzae is a threat to paddy cultivation across the globe. An extensive survey was conducted during kharif seasons of 2012, 2013 and 2014 and 116 isolates of B. oryzae were isolated from the diseased specimens collected from different geographical locations of India representing major rice growing regions. The isolates were charactaerized for morphological traits like colony characters, colony diameter, and sporulation. On the basis of colony morphology and growth pattern on PDA, these isolates were grouped into 8 different categories. Based on colony diameter, all these isolates were grouped into 3 different categories of slow, moderate and fast growing isolates. Maximum sporulation was observed in isolates from Bihar and Jharkhand while the least sporulation was seen in isolates from Gujarat. The molecular characterization carried out on 20 representative isolates using random apmlified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) revealed variability in the isolates. These differences were also observed when cluster analysis was carried out. Out of 20 RAPD and 20 ISSR primers, 5 RAPD and ISSR primers each gave very nice reproducible banding patterns. Polymorphism ranged between 54.0-100% in RAPD markers while it was from 49.2-100% with ISSR markers. This is the first study in our country wherein isolates representing all major rice growing areas of the country has been taken into consideration for variability study and it was observed both by morphological and molecular methods.