Fungus Bipolaris Oryzae Research Articles

Response of Nepalese Rice Landraces to Brown Spot [Bipolaris oryzae (Breda de Haan) Shoemaker] at Rampur, Chitwan, Nepal

Brown spot disease, caused by the fungus Bipolaris oryzae, is a common foliar affliction in rice plants, impacting agricultural yields worldwide. A field experiment was conducted to identify brown spot resistant landraces at Rampur, Chitwan during June to November, 2018. A set of 54 rice genotypes comprising of 52 landraces and two checks (resistant and susceptible) were evaluated for resistance to the disease under field condition in alpha lattice design with three replicates. Area under disease progress curve (AUDPC) values varied significantly among the genotypes. Of the tested 54 genotypes, nine genotypes were found moderately resistant, 38 genotypes susceptible and seven genotypes were found highly susceptible. The maximum incidence (64.9%) of pathogen was found in seed of Hodbachhi followed by Sankharika (64.15%). The minimum average incidence of pathogen was found in check Sabitri (4.05%), which was as par with other 28 genotypes. The yield attributing characters were highly significant among the genotypes. Highest grain yield (1.55 t ha-1) was obtained from Ghusara (1.51 t ha-1) followed by Lalbachhi. Lowest grain yield was obtained from Ghuyeni Saro (0.21 t ha-1) followed by Jaguli Mansuli (0.25 t ha-1). All the yield and yield attributing characters were negatively correlated with AUDPC. Seed-borne infection after harvest was highly significant among the genotypes. The results revealed that among the screened genotypes most of the landraces of rice are susceptible to brown spot.

Morpho-Cultural Variability Characterization of Bipolaris oryzae Causing Brown Leaf Spot of Rice in Jammu Sub-Tropics

Extensive fortnightly surveys were undertaken in major rice growing districts of Jammu division to study cultural and morphological variability amongst the isolates of brown leaf spot disease causing fungus (Bipolaris oryzae). Based on disease severity 24 isolates (BO1 to BO24) were divided into three groups (I, II and III). Group ‘I’ comprised 11 isolates with disease severity values between 51.22-67.44% and categorized under highly virulent and group ‘II’ comprised disease severity values between 43.17-48.17% and were categorized under moderately virulent isolates. Group ‘III’ included eight isolates with disease severity value between 26.11-38.17% and categorized under less virulent isolates. On the basis of colony growth pattern, margin and colour, the isolates were categorized into 4 groups (A, B, C and D). Group A comprised of six isolates had entire margin, circular form, umbonate elevation with smooth surface and black to fluffy growth. Eleven isolates were categorised under group B developed colonies with undulated margin, irregular form, umbonate elevation with grey fluffy growth and greyish colour. Group C comprised three isolates had undulated margin, irregular form, umbonate elevation with smooth surface. Group D contained four isolates developed entire margin, circular form; raised elevation with wrinkled surface, mycelium was grey which turned to black and showed grey to black pigmentation. The largest conidial size was recorded in isolate BO1 (98.43-101×24.54-25.54 µm). The conidia developed mean septa of 4.5-7.4 with straight to curve shaped. The sporulation of different isolates of B. oryzae ranged between 6.1-7.6×106 spores/ml.

In vivo Testing of Plant Extracts in Controlling Rice Brown Spot Disease Through Folia Application

Background: Rice brown spot disease is caused by the fungus Bipolaris oryzae (Breda de Haan), which is one of the most significantly devastating diseases in rice. Nowadays, biological control agents and plant extracts as botanical fungicides are used to develop an alternative method to control this disease and reduce the use of synthetic fungicides. Therefore, the efficacy levels of Hydnocarpus anthelminthicus Pierre ex Laness., Crateva magna (Lour.) DC., Caesalpinia sappan L., Xanthophyllum lanceatum J. J. Sm. and Carallia brachiata (Lour.) Merr. crude extracts were tested in vitro against B. oryzae and their control of rice brown spot disease under greenhouse conditions. Methods: Five plants namely; H. anthelminthicus, C. magna, C. sappan, X. lanceatum and C. brachiata were cleaned with tap water and air dried at 28±2°C then cut into small pieces and ground into fine powder and stored at 4°C until used. Plant crude extracts was prepared using ethanol as solvent. Result: The results showed that the H. anthelminthicus crude extract showed the best antifungal activity against B. oryzae at the highest dose tested, causing 93% mycelial growth inhibition. Under greenhouse testing, the application of the H. anthelminthicus, X. lanceatum, C. brachiata, C. magna and C. sappan crude extracts at a concentration of 50,000 ppm effectively suppressed and reduced rice brown spot incidence caused by B. oryzae when applied once 30 days after transplanting (DAT). Interestingly, the H. anthelminthicus crude extract at a concentration of 10,000 ppm displayed the greatest suppression of the development of rice brown spot disease in terms of disease incidence when applied twice 30 DAT and 45 DAT compared with unprotected control. The results of this study indicated that H. anthelminthicus could provide botanical fungicide protection against rice brown spot disease to reduce the use of synthetic fungicides.

Biochemical Profiling of Resistant Phenotypes Against Bipolaris oryzae Causing Brown Spot Disease in Rice

Brown leaf spot disease of rice is a dominant lethal disease, caused by the fungus Bipolaris oryzae. The pathogen is an obligate parasite and causes qualitative and quantitative damage to rice crop. The objective of the present study was to investigate what extent the defense related biochemical compounds reflect the distinct categories of resistance phenotypes in rice against brown spot disease. This was done by determining the concentration of Catalase (CAT), Phenylalanine ammonia-lyase (PAL), Polyphenol oxidase (PPO), Peroxidase (POD), and β-1,3-Glucanase enzymes in resistant, moderately resistant and susceptible rice genotypes. The disease resistant phenotypes in rice line (PARC-7) reflect the higher accumulation of CAT, PAL, PPO, POD, and β-1,3-Glucanase. The pattern of enzyme accumulation was similar in all resistant genotypes. The rice genotypes with moderately resistant phenotypes showed significant difference with respect to the concentration of biochemical defense-related compounds. The difference in accumulation of defense related enzymes reflected the level of disease severity (% leaf area covered) on resistant and moderately resistant genotypes. The susceptible rice genotypes showed the minimum concentration of these enzymes, with the lowest concentrations found in the rice variety Bas-2000 (80% Disease Index). The differential defense response in resistant and susceptible genotypes suggests that these enzymes can be used as biochemical markers for early detection of disease resistant genotypes. The study of enzyme accumulation at different time points and at different levels of disease severity helps to understand the resistance mechanisms against brown spot disease in rice.

Synthesis and Investigation of Tetrahydro-β-carboline Derivatives as Inhibitors of Plant Pathogenic Fungi.

A series of tetrahydro-ß-carbolines substituted with an alkyl or acyl side chain was synthesized and screened for its antifungal activity against plant pathogenic fungi (Bipolaris oryzae, Curvularia lunata, Fusarium semitectum, and Fusarium fujikuroi). The structure activity relationship revealed that the substituent at the piperidine nitrogen plays an important role for increasing antifungal activities. In this series, 2-octyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole (3g) displayed potent antifungal activities with a minimum inhibitory concentration of 0.1 μg/mL, including good inhibitory activity to the radial growth of fungus at a concentration of 100 μg/mL compared to amphotericin B.

FIELD EVALUATION OF NATIVO 300 SC FUNGICIDE (TRIFLOXYSTROBIN 100 g l-1 + TEBUCONAZOLE 200 g l-1) ON RICE BROWN SPOT (Oryza sativa L.)

Rice brown spot caused by the fungus Bipolaris oryzae is one of the constraints affecting the productivity of rice (Oryza sativa L.) in Côte d'Ivoire. As an effort to find ways of controlling this disease, the efficacy of the fungicide NATIVO 300 SC (trifloxystrobin 100 g l-1 + tebuconazole 200 g l-1) was tested in field conditions at Gbombélo in western Côte d'Ivoire. Five fungicide treatments were studied (water, 2 kg ha-1 of COGA 80 WP (800 g/kg mancozeb), 250 ml ha-1 of NATIVO 300 SC, 300 ml ha-1 of NATIVO 300 SC and 350 ml ha-1 of NATIVO 300 SC), in a Fischer experimental design with four replicates. Results showed a significant effect of fungicides on the severity of brown spot disease, with scores 2 to 3 times lower than in the control plot (water-treated). NATIVO 300 SC at the 350 ml ha-1 dose showed the same severity score as COGA 80 WP, the reference fungicide. Regarding the effect on the yield, NATIVO (300 SC, 350 ml ha-1) performed 9 times better (1.2825 tons ha-1) than the control plot (0.1392 ton ha-1), compared to 6 times for COGA 80 WP (0.9626 ton.ha-1). These results show that NATIVO (300 SC) is as effective, against rice brown spot (Bipolaris oryzae), as COGA 80 WP, the reference fungicide. However, at the dose of 350 ml ha-1, NATIVO 300 SC was the most efficient both from crop protection and agronomic perspective.

Bioreduction of Gold Ions from Anisotropic to Isotropic Nanostructures by NADPH‐Dependent Reductase from Bipolaris oryzae

AbstractHere, we report an eco‐friendly, benign and rapid mycogenic synthesis of gold nanoparticles of various shapes using cell‐free extract of the fungus Bipolaris oryzae (B. oryzae). Three different volumes of cell‐free extract of the fungus were exposed to an aqueous solution of gold chloride and in all three cases, there is a gradual color change from light yellow to pink indicating the formation of gold nanoparticle. Reduced nicotinamide adenine dinucleotide phosphate (NADPH) dependent enzyme present in the cell‐free extract of the fungus B. oryzae leads to the rapid reduction of Au3+ to Au0 within 5–10 min when incubated with an aqueous solution of gold chloride. UV‐visible and fourier transform infra red (FTIR) spectroscopy measurements show the presence of aminoacids, such as tyrosine/phenylalanine and proteins as the possible capping agent. High‐resolution transmission electron microscopy (HR‐TEM) revealed the morphology of the structures were anisotropic triangles, hexagons, decahedrals and isotropic spheres. Isotropic spherical nanoparticles and anisotropic nanoparticles such as triangles, hexagons and decahedrals were produced at higher and lower volumes of the fungal extract, respectively. Rapid and sustainable approach for the production of gold nanoparticles of various shapes such as the one reported has a plethora of applications in the field of life‐sciences and medicine.

Phytochemical Compounds of Branches from P. halepensis Oily Liquid Extract and S. terebinthifolius Essential Oil and Their Potential Antifungal Activity

In the present study, the antifungal activity of wood treated with Pinus halepensis branch n-hexane oily liquid extract (OLE) and Schinus terebinthifolius branch essential oil (EO) was evaluated against the growth of four phytopathogenic fungi—Bipolaris oryzae, Fusarium oxysporum, Fusarium solani, and Rhizoctonia solani. Air-dried wood samples of Pinus roxburghii were autoclaved, and each wood received 100 µL of the concentrated oils from P. halepensis and S. terebinthifolius. The main compounds identified in S. terebinthifolius branch EO were terpinen-4-ol (18.25%), cis-β-terpineol (15.60%), γ-terpinene (12.46%), sabinene (9.83%), α-terpinene (8.56%), and 4-thujanol (6.71%), while the main compounds in P. halepensis branch HeO were 2-undecenal (22.25%), 4-hydroxy-10-methyl-3,4,7,8,9,10-hexahydro-2H-oxecin-2-one (8.43%), (Z)-2-decenal (6.88%), nonanal (5.85%), (2E)-2-decenal (4.65%), (E,E)-2,4-decadienal (4.41%), arachidonic acid methyl ester (4.36%), and 2-(7-heptadecynyloxy)tetrahydro-2H-pyran (4.22%). P. halepensis OLE at a concentration of 3% showed the highest inhibition percentage of fungal growth (IPFG) of B. oryzae, followed by S. terebinthifolius EO at 3% and 2%, with IPFG values of 80%, 74.44%, and 71.66%, respectively. At a concentration of 3%, branch oils from S. terebinthifolius and P. halepensis were found to have the highest IPFG values with 45.55% and 40.55%, respectively, against F. oxysporum growth. Moderate to weak activity was found against F. solani when S. terebinthifolius EO and P. halepensis OLE were applied to wood. EO and OLE-treated wood samples at 3% produced inhibitions of 54.44% and 41.11%, respectively, against R. solani.

Antifungal potential and structure activity relationship of carrot seed constituents.

The aim of this study was to evaluate in vitro antifungal potential of carrot seed extracts, its essential oil, different fractions, isolated compounds, and their derivatives against three phytopathogenic rice fungi (Fusarium moniliforme, Bipolaris oryzae, and Rhizoctonia solani) using poisoned food technique. Carrot seed essential oil was extracted using hydrodistillation method and extracts were prepared using different solvents viz. dichloromethane, hexane, and methanol. The pure compounds daucene, carotol, and daucol were isolated using column chromatography and derivatized using different reagents. The study demonstrated that antifungal potential of all tested compounds varied in a dose dependent manner. Structure activity relationship of isolated and derivatized compounds showed that polar moieties possessed more antifungal potential as compared to non-polar moieties. The results suggested that carrot seed methanol extract and carotol possessed strong antifungal potential as compared to other components tested. PRACTICAL APPLICATIONS: Phytopathogenic fungi are the major problems causing harmful damage to the rice crop. Only available control of these diseases is synthetic fungicides but their repeated use led to serious environmental issues, residual toxicity, and development of resistance. Therefore, it's better to find some natural alternatives. The current study was conducted to evaluate in vitro antifungal potential of carrot seed essential oil, its constituents and extracts against phytopathogenic fungi of rice. The methanol extract and carotol possessed highest antifungal potential which might be due to their polar nature. This information may add a new dimensions to biological activity of these natural molecules mainly in the field of agriculture as fungal diseases are found to be associated with major losses in agriculture. Hence these compounds can act as natural antifungal agents against rice fungi.

Magnesium-induced alterations in the photosynthetic performance and resistance of rice plants infected with Bipolaris oryzae

Brown spot (BS), caused by the fungus Bipolaris oryzae, is one of the most important diseases contracted by rice. We investigated the effect of magnesium (Mg) on the development of BS, caused by Bipolaris oryzae, and the effects of disease development on the photosynthetic performance of rice (Oryza sativa L.) plants (cv. Metica-1) grown in nutrient solutions containing 0.25 or 4.0 mM of Mg. Assessments of BS severity, leaf Mg and pigment concentrations (total chlorophylls and carotenoids), were carried out at 120 h after inoculation, in addition to gas exchange parameters,. Higher leaf concentration of Mg was observed in plants supplied with 4.0 mM Mg than in those supplied with 0.25 mM. The increase in leaf Mg was accompanied by a decrease in BS severity, higher concentration of total chlorophyll and better photosynthetic performance. Plants supplied with 4.0 mM Mg had higher average values for carbon assimilation, stomatal conductance and internal leaf CO2 concentration when compared with plants supplied with 0.25 mM Mg. Conversely, the concentration of carotenoids was lower in plants supplied with the higher Mg rate. These results suggest that Mg suppresses disease severity and preserves photosynthetic performance by allowing for better stomatal conductance and, consequently, greater availability of CO2 at the carboxylation sites.

Effect of lemon grass (Cymbopogen citratus) extract on seed health of rice

Lemon grass extract was evaluated in different dilutions on rice seed health in laboratory and net house experiments. The objectives were to investigate the effect of lemon grass extract on seed-borne pathogen of rice and seedling vigour. Four treatments as 1:1, 1:2, 1:3 dilution of lemon grass extract including a control were studied. Lemon grass extract at 1:1 dilution showed highest germination and vigour index of rice seed and seedlings. It was also found most effective in controlling seed borne fungi of rice. The fungi Bipolaris oryzae, Alternaria padwickii, Curvularia lunata, Fusarium moniliforme, Aspergillus and Penicillium spp. were controlled effectively by soaking seeds in the extract of lemon grass at 1:1 dilution for 6 hours.DOI: http://dx.doi.org/10.3329/brj.v17i1-2.20904Bangladesh Rice j. 2013, 17(1&2): 105-108

Antimicrobial activity of UV-induced phenylamides from rice leaves.

Rice produces a wide array of phytoalexins in response to pathogen attacks and UV-irradiation. Except for the flavonoid sakuranetin, most phytoalexins identified in rice are diterpenoid compounds. Analysis of phenolic-enriched fractions from UV-treated rice leaves showed that several phenolic compounds in addition to sakuranetin accumulated remarkably in rice leaves. We isolated two compounds from UV-treated rice leaves using silica gel column chromatography and preparative HPLC. The isolated phenolic compounds were identified as phenylamide compounds: N-trans-cinnamoyltryptamine and N-p-coumaroylserotonin. Expression analysis of biosynthetic genes demonstrated that genes for arylamine biosynthesis were upregulated by UV irradiation. This result suggested that phenylamide biosynthetic pathways are activated in rice leaves by UV treatment. To unravel the role of UV-induced phenylamides as phytoalexins, we examined their antimicrobial activity against rice fungal and bacterial pathogens. N-trans-Cinnamoyltryptamine inhibited the growth of rice brown spot fungus (Bipolaris oryzae). In addition to the known antifungal activity to the blast fungus, sakuranetin had antimicrobial activity toward B. oryzae and Rhizoctonia solani (rice sheath blight fungus). UV-induced phenylamides and sakuranetin also had antimicrobial activity against rice bacterial pathogens for grain rot (Burkholderia glumae), blight (Xanthomonas oryzae pv. oryzae) and leaf streak (X. oryzae pv. oryzicola) diseases. These findings suggested that the UV-induced phenylamides in rice are phytoalexins against a diverse array of pathogens.

Red‐Light‐Induced Resistance to Brown Spot Disease Caused by Bipolaris oryzae in Rice

AbstractIn this study, the protective effect of red light against the brown spot disease caused by the fungus Bipolaris oryzae in rice was investigated. Lesion formation was significantly inhibited on detached leaves that were inoculated with B. oryzae and kept under red for 48 h, but it was not inhibited when the leaves were kept under natural light or in the dark. The protective effect was also observed in intact rice plants inoculated with B. oryzae; the plants survived under red light, but most of them were killed by infection under natural light or dark condition. Red light did not affect fungal infection in onion epidermis cells or heat‐shocked leaves of rice, and it did not affect cellulose digestion ability; this suggested that the protective effect is due to red‐light‐induced resistance. In addition, the degree of protection increased as the red light dosage increased, regardless of the order of the red light and natural light period, indicating that red‐light‐induced resistance is time dependent. Feeding of detached leaves with a tryptophan decarboxylase inhibitor, s‐α‐fluoromethyltryptophan (0.1 mm), for 24 h inhibited the development of resistance in response to red light irradiation. Suppression of resistance was also observed in leaves treated with a phenylalanine ammonia‐lyase inhibitor, α‐aminooxy acetic acid (0.5 mm). These results suggest that the tryptophan and phenylpropanoid pathways are involved in the red‐light‐induced resistance of rice to B. oryzae.

Effects of slag-based silicon fertilizer on rice growth and brown-spot resistance.

It is well documented that slag-based silicon fertilizers have beneficial effects on the growth and disease resistance of rice. However, their effects vary greatly with sources of slag and are closely related to availability of silicon (Si) in these materials. To date, few researches have been done to compare the differences in plant performance and disease resistance between different slag-based silicon fertilizers applied at the same rate of plant-available Si. In the present study both steel and iron slags were chosen to investigate their effects on rice growth and disease resistance under greenhouse conditions. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the effects of slags on ultrastructural changes in leaves of rice naturally infected by Bipolaris oryaze, the causal agent of brown spot. The results showed that both slag-based Si fertilizers tested significantly increased rice growth and yield, but decreased brown spot incidence, with steel slag showing a stronger effect than iron slag. The results of SEM analysis showed that application of slags led to more pronounced cell silicification in rice leaves, more silica cells, and more pronounced and larger papilla as well. The results of TEM analysis showed that mesophyll cells of slag-untreated rice leaf were disorganized, with colonization of the fungus (Bipolaris oryzae), including chloroplast degradation and cell wall alterations. The application of slag maintained mesophyll cells relatively intact and increased the thickness of silicon layer. It can be concluded that applying slag-based fertilizer to Si-deficient paddy soil is necessary for improving both rice productivity and brown spot resistance. The immobile silicon deposited in host cell walls and papillae sites is the first physical barrier for fungal penetration, while the soluble Si in the cytoplasm enhances physiological or induced resistance to fungal colonization.

ChemInform Abstract: 3‐Anhydro‐6‐hydroxy‐ophiobolin A (I), a New Sesterterpene Inhibiting the Growth of Methicillin‐Resistant Staphylococcus aureus and Inducing the Cell Death by Apoptopsis on K562, from the Phytopathogenic Fungus Bipolaris oryzae.

ChemInformVolume 44, Issue 40 Natural Products ChemInform Abstract: 3-Anhydro-6-hydroxy-ophiobolin A (I), a New Sesterterpene Inhibiting the Growth of Methicillin-Resistant Staphylococcus aureus and Inducing the Cell Death by Apoptopsis on K562, from the Phytopathogenic Fungus Bipolaris oryzae. Hong-Wei Liu, Hong-Wei Liu Inst. Microbiol., Chin. Acad. Sci., Beijing 100190, Peop. Rep. ChinaSearch for more papers by this authoret al. et al., et al. et al. Inst. Microbiol., Chin. Acad. Sci., Beijing 100190, Peop. Rep. ChinaSearch for more papers by this author Hong-Wei Liu, Hong-Wei Liu Inst. Microbiol., Chin. Acad. Sci., Beijing 100190, Peop. Rep. ChinaSearch for more papers by this authoret al. et al., et al. et al. Inst. Microbiol., Chin. Acad. Sci., Beijing 100190, Peop. Rep. ChinaSearch for more papers by this author First published: 12 September 2013 https://doi.org/10.1002/chin.201340201Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume44, Issue40October 1, 2013 RelatedInformation

Effect of Zinc on the Development of Brown Spot in Rice

AbstractBrown spot, caused by the fungus Bipolaris oryzae, is one of the most destructive diseases of rice. This study investigated the effect of zinc rates on the development of brown spot in rice. Rice plants (cv. ‘Metica‐1′) were grown in hydroponic culture amended with Zn rates (applied as ZnSO4.7H2O) of 0, 0.5, 1, 2 and 4 μm and inoculated with B. oryzae. The foliar concentration of Zn was determined. Leaf samples were assessed for disease severity, and then, area under brown spot progress curve (AUBSPC) was calculated. The relationship between Zn concentrations on leaf tissues and the rates of this micronutrient was best described by a positive linear regression model, while the relationship between the Zn rates and the AUBSPC was best described with a positive quadratic regression model. The correlation between Zn concentrations on leaf tissues and AUBSPC was positive and significant (r = 0.68, P < 0.05). The results from this study showed that high foliar concentration of Zn was associated with increasing rice susceptibility to brown spot.

3-Anhydro-6-hydroxy-ophiobolin A, a new sesterterpene inhibiting the growth of methicillin-resistant Staphylococcus aureus and inducing the cell death by apoptosis on K562, from the phytopathogenic fungus Bipolaris oryzae

A new ophiobolin derivative, 3-anhydro-6-hydroxy-ophiobolin A (1), as well as two known ophiobolin derivatives 3-anhydro-ophiobolin A (2) and 3-anhydro-6-epi-ophiobolin A (3) were isolated from the PDB culture of a phytopathogenic fungus Bipolaris oryzae. The structure of 1 was elucidated through 2D NMR and other spectroscopic techniques. Compound 1 exhibited strong antimicrobial activity against Bacille Calmette–Guerin, Bacillus subtilis, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus with MIC value of 12.5μg/mL, and potent antiproliferative activity against cell lines HepG2 and K562 with IC50 of 6.49μM and 4.06μM, respectively. Further studies on the cytotoxicity of compound 1 against K562 cells demonstrated that it induced apoptosis, observed by flow cytometric method. Preliminary structure–activity relationships of these ophiobolins and the mechanism of apoptosis induced by 1 were analyzed.

Rice Resistance to Brown Spot Mediated by Nitrogen and Potassium

This study was undertaken to investigate the effects of both nitrogen (N) and potassium (K) rates on rice resistance to brown spot, caused by the fungus Bipolaris oryzae. Rice plants (cultivar `Metica 1') were grown in soil corrected with 0, 25, 50, 75 and 100 mg of N/kg (as NH 4 NO 3 ) of soil as well as with 25, 50, 75, 125 and 150 mg of K/kg (as KCl) of soil. Thirty-three-day-old plants were inoculated with a suspension of Bipolaris oryzae conidia and the incubation period (IP), number of lesions (NL) per cm 2 of leaf area and disease severity was evaluated. Disease severity was scored at 24, 48, 72, 96, 120 and 144 h after inoculation and data were used to obtain the area under brown spot progress curve (AUBSPC). Soil plant analysis development (SPAD) index, plant dry weight and concentration of N and K in leaf tissues were also determined for both non-inoculated (NI) and inoculated (IN) plants. Concentration of N in leaf tissue increased as the N rates in the soil increased. Concentration of K in leaf tissue increased sharply as the K rates in the soil increased for both NI and IN plants. Concentration of K in leaf tissue was not affected by N rates. The IP increased as the N rates increased, but was somewhat less impacted by increasing K rates. The NL decreased as the N rates increased. The NL dramatically declined at the highest K rates. The AUBSPC dramatically declined as the N and K rates in the soil increased. SPAD index values increased as the N and K rates in the soil increased for both NI and IN plants. Plant dry weight increased as the N and K rates in the soil increased for both NI and IN plants. Results from this study suggest that combining high N and K rates may contribute to reducing the intensity of brown spot in rice while improving plant development.

Cloning and expression analysis of two opsin-like genes in the phytopathogenic fungusBipolaris oryzae

Two opsin-like genes, OPS1 and OPS2, were identified from a subtracted cDNA library for the identification of near-UV (NUV) radiation-enhanced genes using suppression subtractive hybridization methods in the brown leaf spot fungus Bipolaris oryzae. The OPS1 and OPS2 genes encode predicted proteins of 306 and 304 amino acids, respectively. Real-time PCR analysis showed that the OPS1 transcript is expressed weakly in mycelia under dark conditions but shows enhanced expression after NUV irradiation. By contrast, the OPS2 transcript is constitutively expressed at a high level in mycelia under dark conditions but is only weakly enhanced after NUV irradiation. These enhancement patterns of OPS1 and OPS2 gene expression after NUV irradiation did not occur in the blue-light regulator 1 (BLR1)-deficient mutant, suggesting that NUV radiation-enhanced gene expression of OPS1 and OPS2 could be controlled by the BLR1 in B. oryzae.

Defective Active Silicon Uptake Affects Some Components of Rice Resistance to Brown Spot

Rice is known to accumulate high amounts of silicon (Si) in plant tissue, which helps to decrease the intensity of many economically important rice diseases. Among these diseases, brown spot, caused by the fungus Bipolaris oryzae, is one of the most devastating because it negatively affects yield and grain quality. This study aimed to evaluate the importance of active root Si uptake in rice for controlling brown spot development. Some components of host resistance were evaluated in a rice mutant, low silicon 1 (lsi1), defective in active Si uptake, and its wild-type counterpart (cv. Oochikara). Plants were inoculated with B. oryzae after growing for 35 days in a hydroponic culture amended with 0 or 2 mMol Si. The components of host resistance evaluated were incubation period (IP), relative infection efficiency (RIE), area under brown spot progress curve (AUBSPC), final lesion size (FLS), rate of lesion expansion (r), and area under lesion expansion progress curve (AULEPC). Si content from both Oochikara and lsi1 in the +Si treatment increased in leaf tissue by 219 and 178%, respectively, over the nonamended controls. Plants from Oochikara had 112% more Si in leaf tissue than plants from lsi1. The IP of brown spot from Oochikara increased approximately 6 h in the presence of Si and the RIE, AUBSPC, FLS, r, and AULEPC were significantly reduced by 65, 75, 33, 36, and 35%, respectively. In the presence of Si, the IP increased 3 h for lsi1 but the RIE, AUBSPC, FLS, r, and AULEPC were reduced by only 40, 50, 12, 21, and 12%, respectively. The correlation between Si leaf content and IP was significantly positive but Si content was negatively correlated with RIE, AUBSPC, FLS, r, and AULEPC. Single degree-of-freedom contrasts showed that Oochikara and lsi1 supplied with Si were significantly different from those not supplied with Si for all components of resistance evaluated. This result showed that a reduced Si content in tissues of plants from lsi1 dramatically affected its basal level of resistance to brown spot, suggesting that a minimum Si concentration is needed. Consequently, the results of this study emphasized the importance of an active root Si uptake system for an increase in rice resistance to brown spot.